CN115954401A - Heterojunction and photoelectric detector based on platinum diselenide and germanium and preparation method thereof - Google Patents
Heterojunction and photoelectric detector based on platinum diselenide and germanium and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a heterojunction and a photoelectric detector based on platinum diselenide and germanium and a preparation method thereof. In order to prevent the germanium selenide from being generated in the platinum film selenizing process of the germanium substrate, the invention also discloses a method for preparing an insulating layer on the back surface of the germanium substrate of the heterojunction structure, so that the heterojunction structure of platinum diselenide/ultrathin insulating layer/germanium/back surface insulating layer is formed. The heterojunction and the photoelectric detector thereof have the advantages of simple preparation method, low cost and compatibility with silicon technology. The photoelectric detector composed of the heterojunction has the excellent characteristics of zero bias drive, high response rate, high detection rate, high on-off ratio, low dark current, high stability, wide spectral response and the like, and the method paves the way for a new generation of high-performance photoelectric detectors.
Description
Technical Field
The invention relates to the technical field of heterojunction and photoelectric detectors based on heterojunction, in particular to a heterojunction based on platinum diselenide and germanium, a photoelectric detector and a preparation method thereof.
Background
Photodetectors (PDs) are one of the most important optoelectronic devices that convert incident optical signals into electrical signals. Photodetectors (PDs) are an important component of optoelectronic systems, and more a critical component of the modern miniaturized electronics industry. The research and application of the photoelectric detector greatly promote the progress and development of society. However, with the rapid development of the times, the problems of the traditional photoelectric detector are slowly revealed. Although the traditional silicon-based photoelectric detection technology is relatively mature, the traditional silicon-based photoelectric detection technology falls into a bottleneck period in the aspects of working wavelength, responsivity, speed and the like, and meanwhile, the silicon-based photoelectric detector is only suitable for detection of 200-1100 nm wavelength and has no light response to other wavelengths. Other conventional materials for photodetectors (including cadmium telluride, gallium arsenide, and mercury cadmium telluride) have a measurement band covering the detection in the infrared spectrum, but these types of photodetectors can only achieve high sensitivity detection under relatively harsh conditions (e.g., low temperature), and are also subject to complicated manufacturing techniques. With the development of technologies such as communication, intelligent driving and the like, the development of a photoelectric detector with excellent characteristics for 1550nm wavelength detection is more and more critical, a detector based on germanium (Ge) is suitable for 800-1800nm wavelength detection, the responsivity of a commercial P-I-N structure device is less than 1.0A/W, the dark current is large (about 1 muA), the response rise time is long (about 3 mus), and the preparation process is complex [ APL photon.6,041302 (2021) ]. Future detectors should have high specific detection rate, extremely low dark current, wide spectral response and other parameter indexes.
Platinum diselenide (PtSe) as an emerging two-dimensional material for group 10 transition metal chalcogenides 2 ) The material has the common characteristics of two-dimensional materials with wide adjustable band gap, high carrier mobility and other excellent performances; at the same time, ptSe 2 Also has own unique and excellent characteristics, such as PtSe 2 Having a strong air stability and a strong number of layers related band structure, e.g. single layer PtSe 2 Is a semiconductor (forbidden band width about 1.2 eV), and PtSe is produced as the thickness increases 2 Can change from a semiconductor characteristic of a thinner thickness (e.g., single layer, few layers) to a higher oneNarrow bandgap semiconductor, semi-metallic properties of thick bulk materials, layered PtSe 2 The thin film has expandability and controllability, which make PtSe 2 Has potential application in the infrared neighborhood. For PtTe 2 In other words, although Te and Se are the same group element, ptTe 2 Electronic properties different from PtSe 2 A material; research shows that PtTe 2 Belonging to the semimetallic nature (George Zhang et al, appl. Phys. Lett.114,253102 (2019)). The different forbidden band widths lead to different absorption of light and different light response characteristics of the material.
Currently, two-dimensional PtSe 2 Thin film synthesis processes are also well established and include mechanical lift-off, chemical Vapor Deposition (CVD), thermally Assisted Conversion (TAC), molecular Beam Epitaxy (MBE), and Chemical Vapor Transport (CVT). Wherein, the TAC preparation cost is low, and the high-quality two-dimensional PtSe can be prepared in a large scale at a lower temperature (400 ℃) 2 Thin film and is compatible with conventional germanium processes. Briefly, ptSe 2 Has the advantages of excellent photoelectric characteristics, the compatibility with the traditional silicon CMOS process and the like, and the advantages of large-scale production and the like enable the PtSe 2 Has potential application in industrial and commercial fields. Recently, ptSe has been reported 2 The responsivity of the device in a communication waveband (1550 nm) is 0.766A/W, the specific detectivity is low, the dark current is large (-0.31 muA), the response time is long (-55 mus), namely, the device has defects in main parameters, and the practical application of the device is limited.
Disclosure of Invention
Aiming at the defects in the field, the invention provides a heterojunction and a photoelectric detector based on platinum diselenide (PtSe 2) and germanium (Ge) and a preparation method thereof. The photoelectric detector composed of the heterojunction has the excellent characteristics of zero bias drive, high response rate, high detection rate, low dark current, high stability, wide spectral response and the like, and paves the way for a new generation of photoelectric detector.
Specifically, the invention is realized by the following technical scheme:
according to a first aspect of the invention, a platinum diselenide and germanium based heterojunction is provided, and is a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure, and comprises a germanium layer, a platinum diselenide layer, an ultrathin insulating layer and a back insulating layer;
the ultrathin insulating layer is arranged above the germanium layer;
the platinum diselenide layer is positioned above the ultrathin insulating layer;
the back side insulating layer is below the germanium layer.
The ultrathin insulating layer is formed by non-conductive materials, and the function of the ultrathin insulating layer is mainly embodied in that the heterojunction interface potential barrier is improved, but the tunneling of charges is not blocked, and meanwhile, the interface state and the surface state can be passivated.
Further, the thickness of the ultra-thin insulating layer is 1 to 6nm, preferably 1 to 4nm.
Furthermore, the thickness of the platinum diselenide layer is 0.7nm-50.0nm, and absorption spectrum tests of experiments show that the platinum diselenide film prepared by the method has semiconductor characteristics.
Further, the material of the ultrathin insulating layer and the back insulating layer comprises any one or more of silicon dioxide, aluminum oxide, graphene oxide, boron nitride and insulating polymer; preferably, the insulating layer material is aluminum oxide.
Further, the back side insulating layer can prevent the germanium layer from being selenized into germanium selenide; preferably, the back insulating layer is selected from alumina; preferably, the thickness of the back side insulating layer is about 10nm.
According to a second aspect of the present invention, there is provided a method for preparing a heterojunction based on platinum diselenide and germanium, the method for preparing the heterojunction comprising:
manufacturing an ultrathin insulating layer above the germanium layer to form an ultrathin insulating layer/germanium structure;
manufacturing a back insulating layer below the germanium layer to form an ultrathin insulating layer/germanium/back insulating layer structure;
and preparing a platinum diselenide film above the ultrathin insulating layer to form a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure.
Further, the preparation method of the heterojunction specifically comprises the following steps:
(1) Preparing an insulating layer on a germanium substrate;
(2) Setting a working area on the insulating layer/germanium substrate, wherein the working area is used for constructing a platinum diselenide/ultrathin insulating layer/germanium heterojunction;
(3) Etching the insulating layer of the working area by using an etching solution to expose germanium, wherein the insulating layer which is not etched outside the working area can isolate the working area;
(4) Preparing an ultrathin insulating layer in the working area to form an ultrathin insulating layer/germanium structure;
(5) Preparing a back insulating layer on the back of the germanium substrate to form an ultrathin insulating layer/germanium/back insulating layer structure;
(6) And preparing a platinum diselenide film in the working area to form a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure.
Specifically, with germanium as a substrate and alumina as an ultrathin insulating layer, a silicon dioxide layer is prepared on the germanium substrate by magnetron sputtering in the step (1) of heterojunction preparation of the invention. And (3) setting a working area in the step (2), namely transferring the defined pattern of the working area to the substrate through the steps of glue homogenizing, prebaking, exposing, developing and film hardening sequentially in an ultra-clean room. Then, in step (3), the silicon dioxide on the germanium in the working area is preferably etched by hydrofluoric acid buffer solution, because the etching process is stable. In the steps (4) and (5), alumina is prepared by atomic layer deposition to be used as an insulating layer. And finally, preparing the platinum diselenide thin film in the working area in the step (6) to form a platinum diselenide thin film/aluminum oxide/germanium/aluminum oxide heterojunction structure.
The invention adopts the control of magnetron sputtering time and power to realize the effective regulation and control of the thickness of the heterostructure platinum diselenide film, and the principle is as follows: the platinum diselenide thin film is formed by selenizing a magnetron sputtering platinum thin film, wherein the thickness of the platinum thin film and the thickness of the platinum diselenide thin film after selenization have a linear relation to a certain extent. Therefore, the thickness of the platinum film can be controlled by controlling the power and time of the magnetron sputtering, and the thickness of the platinum diselenide film can be further controlled. The platinum diselenide thin films with different thicknesses have different energy band structures, such as forbidden band widths; therefore, the thickness of the platinum diselenide can be controlled to adjust the light absorption and the photoelectric response of the heterojunction, and the characteristics of the platinum diselenide/insulating layer/germanium heterojunction photoelectric detector are influenced.
The ultrathin insulating layer can change or increase a charge injection potential barrier of a platinum diselenide/germanium interface, so that the transport property of charges is regulated and controlled, for example, under the condition of heterojunction zero bias, multi-photon diffusion is blocked to reduce dark current; the ultra-thin insulating layer cannot block charge tunneling when biased. Meanwhile, the insulating layer can passivate an interface state and a surface state and reduce carrier recombination. The advantage of small dark current is that the specific detection rate and the on-off ratio of the photoelectric detector can be greatly improved, i.e. the weak light detection capability of the detector is effectively improved;
the back insulating layer can effectively protect the germanium substrate and prevent the germanium substrate from reacting to generate germanium selenide in the platinum film selenizing process.
The ultrathin insulating layer or the back insulating layer can be prepared by different preparation methods according to different insulating layer materials, such as insulating high polymer materials, and can be prepared by a solution method such as a spin coating method; for boron nitride (h-BN), the transfer method can be adopted or the existing technology can be directly adopted to prepare on germanium; for alumina, electron beam deposition, atomic layer deposition, and the like can be used.
The platinum diselenide thin film prepared by the present invention may be prepared by conventional methods such as Chemical Vapor Deposition (CVD), thermal Assisted Conversion (TAC), molecular Beam Epitaxy (MBE), chemical Vapor Transport (CVT), etc., as described above. The precursor which can be selected by the heat-assisted conversion method is a platinum film and selenium powder, the reaction temperature of the precursor is lower than 400 ℃, the precursor reacts in an inert atmosphere to form a platinum diselenide film, and the process is compatible with a silicon-based CMOS (complementary metal oxide semiconductor) process.
According to a third aspect of the invention there is provided a photodetector based on a heterojunction of platinum diselenide and germanium, the photodetector comprising a heterojunction as described in the first aspect of the invention and an electrode in electrical contact with the heterojunction;
the electrodes in electrical contact with the heterogeneous solid layer include an electrode in electrical contact with the platinum diselenide layer and an electrode in electrical contact with the germanium layer.
Further, the electrode is selected from a metal material or a non-metal conductor material.
Further, the non-metallic conductor material is selected from graphene, PEDOT PSS. The PEDOT and PSS refer to a high-molecular polymer aqueous solution with high conductivity, and aqueous solutions with different conductivities can be obtained according to different formulas. The product is composed of PEDOT and PSS. PEDOT is a polymer of EDOT (3, 4-ethylenedioxythiophene monomer) and PSS is polystyrene sulfonate.
According to a fourth aspect of the present invention, there is provided a method for manufacturing a photodetector based on a heterojunction of platinum diselenide and germanium, the method for manufacturing the photodetector including:
preparation of platinum diselenide and germanium based heterojunctions: respectively manufacturing an ultrathin insulating layer and a back insulating layer above and below the germanium layer, and preparing a platinum diselenide film on the ultrathin insulating layer to form a platinum diselenide/ultrathin insulating layer/germanium heterojunction structure;
preparing a photoelectric detector based on a heterojunction of platinum diselenide and germanium: and preparing electrodes on the platinum diselenide layer and the germanium layer based on the obtained heterojunction of the platinum diselenide and the germanium to complete the preparation of the photoelectric detector.
The electrode can be prepared by a suitable preparation method, such as thermal evaporation, electron beam deposition, sputtering, solution method, and the like, according to the characteristics of the electrode material.
The invention also provides application of the heterojunction based on the platinum diselenide thin film and germanium as a photoelectric detector. Due to the photoelectric response of the platinum diselenide and the germanium and the existence of a thin aluminum oxide layer at the interface of the platinum diselenide and the germanium, the photoelectric detector has the characteristics of high efficiency, wide spectral response and the like. Since platinum diselenide is a P-type semiconductor and substrate germanium is an N-type semiconductor, electrons in the N-type semiconductor diffuse towards the P-type semiconductor after the platinum diselenide and the substrate germanium form a heterojunction, and holes in the P-type semiconductor diffuse towards the N-type semiconductor. Due to the diffusion of electrons and holes, uncompensated, fixed donor ions (positive ions) and acceptor ions (negative ions) are present on the N-side and P-side, respectively, close to each other, and the space charges establish an electric field, i.e. a space charge region electric field, the direction of which is directed from the N-type semiconductor to the P-type semiconductor. The existence of the space charge area electric field can enable the photoelectric detector to rapidly separate the photogenerated carriers generated by incident light under zero bias voltage to form photocurrent.
The ultrathin insulating layer in the platinum diselenide film/insulating layer/germanium/insulating layer heterojunction can increase the platinum diselenide/germanium interface potential barrier, so that the transport characteristics of charges can be regulated and controlled, for example, the charges are blocked from diffusing under zero bias of the heterojunction to reduce dark current, but due to the ultrathin characteristic, the insulating layer can not block the charges from tunneling under bias. On the other hand, the ultrathin insulating layer can passivate a heterojunction interface state and a surface state and reduce carrier recombination. In a word, the existence of the insulating layer can increase the PN junction potential barrier and reduce the dark current under different bias conditions, thereby achieving the purposes of improving the switching ratio, the responsivity and the ratio detectivity.
Compared with the prior art, the invention has the main advantages that:
(1) Compared with the platinum diselenide/germanium heterojunction structure in the prior art, the platinum diselenide/germanium heterojunction structure has a thin insulating layer between the platinum diselenide and the germanium.
(2) The preparation method of the platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure is simple, the high-quality platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction heterostructure can be obtained in a short time at a low temperature (400 ℃) by using simpler equipment, the preparation process of the platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction heterostructure is compatible with a silicon-based CMOS (complementary metal oxide semiconductor) process, the preparation efficiency and yield are improved, and the preparation cost is low.
(3) The platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure has excellent stability.
(4) Platinum diselenide/ultrathin insulating layer/germanium/back using the inventionThe photoelectric detector prepared by the surface insulating layer heterojunction has the excellent characteristics of zero bias drive, low dark current, high response rate, high detection rate, high on-off ratio, high stability, wide spectral response and the like. For example, the responsivity, specific detectivity and rise/fall time under a 1550nm light source can reach 4.24A/W and 4.47 multiplied by 10 9 Jones, 94.4/67.1. Mu.s. The light response is excellent from ultraviolet to infrared, the spectrum range includes 375nm to 1550nm, and the whole photoelectric response characteristic is obviously superior to that of the prior art.
The present invention focuses only on two-dimensional PtSe 2 Heterojunctions with Ge are illustrated, but in two-dimensional material systems there are other semiconductor two-dimensional materials that are narrow band gaps when the thickness is less than a certain value, such as PtS 2 、PdS 2 、PdSe 2 The inventive idea or structure is equally applicable to heterojunctions of these two-dimensional materials with germanium and to its application as photodetectors.
Drawings
FIG. 1 is a schematic diagram of the structure of a platinum diselenide and germanium heterojunction-based photodetector of the present invention;
FIG. 2 is a flow chart of the fabrication of a platinum diselenide and germanium heterojunction based photodetector and array thereof in accordance with the present invention;
FIG. 3 is a representation of platinum diselenide thin film prepared according to the present invention; FIG. 3 (a) is a SEM photograph; FIG. 3 (b) is a Raman spectrum of platinum diselenide, showing that PtSe was obtained 2 A film;
fig. 4 is a graph (zero bias) representing photoelectric properties of the photodetector of the platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction prepared in example 1 under the irradiation of a 1550nm light source; FIG. 4 (a) is a graph of I-V of a device under illumination by 1550nm light at various intensities; FIG. 4 (b) is a graph of I-T of the device under different intensities of 1550nm light; FIG. 4 (c) is the response time of the device under 1550nm light source; FIG. 4 (d) is a graph showing the relationship between the intensity of a light source and the responsivity and the specific detectivity of a device under the irradiation of a 1550nm light source;
fig. 5 is a photo-electric performance characterization diagram (zero bias) of the photo-detector of platinum diselenide/ultra-thin insulating layer/germanium/back insulating layer heterojunction prepared in example 1 under the irradiation of other light sources; FIG. 5 (a) is an I-V diagram of the device under different intensities of 375nm light source; FIG. 5 (b) is an I-T diagram of the device under different intensities of 375nm light source; FIG. 5 (c) is the relationship between the light source intensity and the responsivity and the specific detectivity of the device under the 375nm light source irradiation; FIG. 5 (d) is an I-V diagram of the device under different intensities of 532nm light source; FIG. 5 (e) is an I-T diagram of the device under different intensities of 532nm light source; FIG. 5 (f) is the relationship between the light source intensity and responsivity and the specific detectivity of the device under 532nm light source illumination; FIG. 5 (g) is an I-V diagram of the device under 940nm light source illumination of different intensities; FIG. 5 (h) is an I-T diagram of the device under 940nm light source illumination of different intensities; FIG. 5 (i) is a graph showing the relationship between the intensity of a light source and the responsivity and the specific detectivity of a device under the illumination of a 940nm light source;
fig. 6 is a graph comparing the photoelectric performance of the photodetector of platinum diselenide/ultrathin insulating layer/germanium/backside insulating layer heterojunction of example 1 with the photodetector of platinum diselenide/germanium/insulating layer heterojunction of comparative example 1 (zero bias); FIG. 6 (a) is an I-V diagram of two devices in the dark state; FIG. 6 (b) is an I-T diagram of two devices under illumination by light sources of different wavelengths; FIG. 6 (c) is a graph showing the response of two devices under different wavelengths of light; FIG. 6 (d) is a graph showing the specific detectivity variation of two devices under different wavelength light source illumination;
table 1 shows a summary of the performance of the devices of example 1, example 2, example 3, example 4 and comparative example 1 and other reported photodetector performance parameters for similar device structures.
Detailed Description
The invention is further described with reference to the following drawings and specific examples. It should be understood that these examples and comparative examples are only described with alumina as the material of the insulating layer, and are only intended to illustrate the present invention and not to limit the scope of the present invention. Experimental procedures without specific conditions noted in the following examples, generally according to conventional conditions, or according to conditions recommended by the manufacturer.
The schematic flow chart of the preparation process of the platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction and the photoelectric detector based on the heterojunction is shown in fig. 2.
Example 1
Referring to fig. 1 and fig. 2, the basic structure and the manufacturing steps of the photodetector of the present invention are as follows:
s1, preparing a clean germanium substrate, cutting a germanium sheet into square substrates with the size of 15mm multiplied by 15mm by using a diamond pen, sequentially putting the square substrates into acetone, absolute ethyl alcohol and deionized water for ultrasonic cleaning, and finally taking out the square substrates and drying the square substrates by using nitrogen.
S2, preparing an insulating layer on a germanium substrate: a layer of 200nm silicon dioxide is prepared on an exposed germanium substrate through magnetron sputtering to serve as an insulating layer.
And S3, defining 4 multiplied by 4 working areas on the germanium substrate by using a conventional micro-nano processing technology, namely photoetching, including spin coating of photoresist, exposure, development and the like.
S4, corroding the insulating layer of the working area: the silicon dioxide/germanium substrate with the working area (pattern) is put in the prepared hydrofluoric acid buffer solution for corrosion for a proper time, the silicon dioxide layer of the working area is corroded to expose germanium, and then the silicon dioxide layer is taken out and put into deionized water for rinsing.
S5, removing the photoresist: and (3) placing the silicon dioxide/germanium substrate subjected to silicon dioxide corrosion in the working area into photoresist corrosive liquid to remove photoresist, then placing the silicon dioxide/germanium substrate into deionized water to rinse, and finally blowing dry by using nitrogen, namely, for the whole silicon dioxide/germanium substrate, only germanium exists in the working area, and silicon dioxide/germanium exists outside the working area.
The insulating layer still remaining outside the active area serves to separate the active area from the non-active area.
S6, preparing an insulating layer in a working area: in this embodiment, an atomic layer deposition technique is used to prepare a 4nm alumina insulating layer, i.e., alumina/germanium, on the exposed germanium surface of the working area.
And S7, preparing a back insulating layer on the back of the germanium substrate.
In the embodiment, an atomic layer deposition technology is adopted to prepare a 10nm alumina insulating layer on the back of a germanium substrate, namely alumina/germanium/alumina is formed in a working area; the silicon oxide insulating layer prepared on the back side of the germanium substrate can prevent the germanium layer from being selenized into germanium selenide.
S8, depositing a platinum film: a platinum film is deposited in a working area with a thin insulating layer by a patterning process. In the embodiment, the platinum films with different thicknesses are prepared by controlling the sputtering power and time of a magnetron sputtering system, namely platinum/aluminum oxide/germanium/aluminum oxide is formed in a working area;
and S9, forming the platinum selenide thin film. Through a heat-assisted conversion process, the deposited platinum film is synthesized into a high-quality platinum diselenide film through a selenization process, so that a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure, namely PtSe 2 /Al 2 O 3 /Ge/Al 2 O 3 . By this step, al is added to 2 O 3 Preparation of PtSe on Ge 2 The characterization results of the film are shown in FIG. 3.
The insulating layer material of the invention can be one or more of silicon dioxide, aluminum oxide, graphene oxide, boron nitride, insulating polymer and other materials. In this embodiment, alumina is used as the insulating layer. Different preparation methods can be adopted for preparing different insulating layers according to different specific materials, and the preparation methods comprise technical methods such as a solution method, atomic layer deposition, transfer and the like.
In this embodiment, conventional techniques such as sputtering, e-beam deposition, etc. may be used to deposit the silicon dioxide, platinum film.
In this embodiment, the fabrication of the photodetector may be accomplished by fabricating the electrode using conventional techniques such as sputtering, electron beam deposition, spin coating, and the like.
It should be noted that, in the above preparation steps, the order of the preparation steps may be properly adjusted according to actual situations, and the present invention is not limited thereto.
For example 1, the present invention characterizes the performance of the prepared platinum diselenide/ultra-thin insulating layer/germanium/back surface insulating layer heterojunction photodetector, and the characterization results are shown in fig. 4 and 5.
Fig. 4 is a graph (zero bias) representing photoelectric properties of the photoelectric detector of the platinum diselenide/ultra-thin insulating layer/germanium/back insulating layer heterojunction prepared in example 1 under the irradiation of a 1550nm light source; FIG. 4 (a) is a graph of I-V of a device under illumination by 1550nm light at various intensities; FIG. 4 (b) is a graph of I-T of the device under different intensities of 1550nm light; FIG. 4 (c) is the response time of the device under 1550nm light source; FIG. 4 (d) is a graph showing the relationship between the intensity of a light source and the responsivity and the specific detectivity of a device under the irradiation of a 1550nm light source;
wherein, the responsivity is a physical quantity describing the photoelectric conversion capability of the device, and the responsivity is related to the device material and the optical wavelength. Specific detectivity is expressed as the detector unit surface area (1 cm) 2 ) And spectral detectivity per bandwidth (1 Hz). The method is a parameter for representing the capability of a detector for detecting weak light signals, and the calculation formula is as follows:
in the formula:
r-responsivity (A/W);
I p -a photocurrent (A);
I d -dark current (a);
p-illumination intensity (W);
d x-specific detection rate (cmHz) 1/2 /W -1 ,Jones)；
A-device effective area (cm) 2 )；
B-measuring the circuit bandwidth (Hz);
NEP-noise equivalent power (WHz) 11/2 )；
e-element charge (1.602X 10) -19 C)。
Fig. 5 is a diagram (zero bias) of photoelectric property characterization of the photodetector of the platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction prepared in example 1 under the irradiation of other light sources; FIG. 5 (a) is an I-V diagram of a device under different intensities of 375nm light source; FIG. 5 (b) is an I-T diagram of the device under different intensities of 375nm light source; FIG. 5 (c) is a graph showing the relationship between the intensity of a light source and the responsivity and the specific detectivity of a device under the illumination of a 375nm light source; FIG. 5 (d) is an I-V diagram of the device under different intensities of 532nm light source; FIG. 5 (e) is an I-T diagram of the device under different intensities of 532nm light source; FIG. 5 (f) is the relationship between the light source intensity and responsivity and the specific detectivity of the device under 532nm light source illumination; FIG. 5 (g) is an I-V diagram of the device under 940nm light source illumination of different intensities; FIG. 5 (h) is an I-T diagram of the device under 940nm light source illumination of different intensities; FIG. 5 (i) is a graph showing the relationship between the intensity of a light source and the responsivity and the specific detectivity of a device under the illumination of a 940nm light source;
example 2
In this embodiment, the ultra-thin insulating layer is alumina with a thickness of 6nm, i.e., in this embodiment, the step s6. The preparation of the insulating layer in the working area is to prepare an alumina insulating layer with a thickness of 6nm, i.e., alumina/germanium, on the exposed germanium surface of the working area by using the atomic layer deposition technique. The remaining preparation steps are the same as in example 1 and are not repeated herein.
Example 3
In the present embodiment, the ultra-thin insulating layer is alumina with a thickness of 1nm, i.e., in the present embodiment, the step s6. Preparing the insulating layer in the working area is to prepare an alumina insulating layer with a thickness of 1nm, i.e., alumina/germanium, on the exposed germanium surface of the working area by using the atomic layer deposition technique. The remaining preparation steps are the same as in example 1 and are not repeated herein.
Example 4
The thickness of the ultra-thin insulating layer in this example is 2nm of silicon dioxide. The preparation method comprises the following steps:
s1, preparing a clean germanium substrate, cutting a germanium sheet into square substrates with the size of 15mm multiplied by 15mm by using a diamond pen, sequentially putting the square substrates into acetone, absolute ethyl alcohol and deionized water for ultrasonic cleaning, and finally taking out the square substrates and drying the square substrates by using nitrogen.
S2, preparing an insulating layer on the germanium substrate: a layer of 200nm silicon dioxide is prepared on an exposed germanium substrate through magnetron sputtering to serve as an insulating layer.
And S3, defining 4 multiplied by 4 working areas on the germanium substrate by using a conventional micro-nano processing technology, namely photoetching, including spin coating of photoresist, exposure, development and the like.
S4, corroding the insulating layer of the working area: placing the silicon dioxide/germanium substrate with the set working area (pattern) in a prepared hydrofluoric acid buffer solution for etching for a proper time, etching the silicon dioxide layer of the working area to leave a silicon dioxide layer with the thickness of 2nm, and then taking out and placing the silicon dioxide layer into deionized water for rinsing.
S5, removing the photoresist: and (3) placing the silicon dioxide/germanium substrate corroded by the silicon dioxide in the working area into photoresist corrosive liquid to remove photoresist, then placing the silicon dioxide/germanium substrate into deionized water to rinse, and finally blowing dry by using nitrogen gas, namely, for the whole silicon dioxide/germanium substrate, 2nm silicon dioxide/germanium exists in the working area, and silicon dioxide/germanium exists outside the working area.
The insulating layer still remained outside the active area is used to separate the active area from the non-active area.
And S6, preparing a back insulating layer on the back of the germanium substrate.
In the embodiment, an atomic layer deposition technology is adopted to prepare a 10nm alumina insulating layer on the back of a germanium substrate, namely 2 nm-silicon oxide/germanium/alumina is formed in a working area; the aluminum oxide insulating layer prepared on the back of the germanium substrate can prevent the germanium layer from being selenized into germanium selenide.
S7, depositing a platinum film: and depositing a platinum film in the working area with the thin insulating layer by adopting a patterning process technology. In the embodiment, the platinum films with different thicknesses are prepared by controlling the sputtering power and time of the magnetron sputtering system, namely platinum/silicon oxide/germanium/aluminum oxide is formed in a working area;
and S8, forming the platinum selenide thin film. Through a heat-assisted conversion process, the deposited platinum film is synthesized into a high-quality platinum diselenide film through a selenization process, so that a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure, namely PtSe, is formed 2 /SO 2 /Ge/Al 2 O 3 . Through the steps in SiO 2 Preparation of PtSe on Ge 2 A film.
The insulating layer material of the invention can be one or more of silicon dioxide, aluminum oxide, graphene oxide, boron nitride, insulating polymer and other materials. In this embodiment, silicon dioxide is used as the insulating layer. Different preparation methods can be adopted for preparing different insulating layers according to different specific materials, and the preparation methods comprise technical methods such as a solution method, atomic layer deposition, transfer and the like.
In this embodiment, conventional techniques such as sputtering, e-beam deposition, etc. may be used to deposit the silicon dioxide, platinum film.
In this embodiment, the fabrication of the photodetector may be accomplished by fabricating the electrode using conventional techniques such as sputtering, electron beam deposition, spin coating, and the like.
It should be noted that, in the above preparation steps, the order of the preparation steps may be properly adjusted according to actual situations, and the present invention is not limited thereto.
Comparative example 1
S1, preparing a clean germanium substrate, cutting a germanium sheet into square substrates with the size of 15mm multiplied by 15mm by using a diamond pen, sequentially putting the square substrates into acetone, absolute ethyl alcohol and deionized water for ultrasonic cleaning, and finally taking out the square substrates and drying the square substrates by using nitrogen.
S2, preparing a layer of 200nm silicon dioxide as an insulating layer on the exposed germanium substrate through magnetron sputtering;
s3, defining 4 multiplied by 4 working areas on the germanium substrate by using a conventional micro-nano processing technology, namely photoetching, including spin-coating photoresist, exposure, development and the like;
s4, corroding the insulating layer of the working area: placing the silicon dioxide/germanium substrate with a set working area (pattern) in a prepared hydrofluoric acid buffer solution for corrosion for a proper time, corroding the silicon dioxide layer of the working area to expose germanium, taking out the silicon dioxide layer and putting the silicon dioxide layer into deionized water for rinsing;
s5, removing the photoresist: placing the silicon dioxide/germanium substrate subjected to silicon dioxide corrosion in the working area into photoresist corrosive liquid to remove photoresist, then placing the silicon dioxide/germanium substrate into deionized water to rinse, and finally blowing dry by using nitrogen gas, namely, for the whole silicon dioxide/germanium substrate, only germanium exists in the working area, and silicon dioxide/germanium exists outside the working area;
s6, preparing an insulating layer on the back of the germanium substrate. In the embodiment, an atomic layer deposition technology is adopted to prepare a 10nm insulating layer on the back of a germanium substrate, namely germanium/aluminum oxide is formed in a working area;
and S7, transferring the platinum selenide thin film. And synthesizing the deposited platinum film into a high-quality platinum diselenide film through a selenization process by a heat-assisted conversion process. Then, the platinum diselenide film is transferred to a working area of the germanium/aluminum oxide substrate through a two-dimensional material transfer process, so that a platinum diselenide/germanium/insulating layer heterojunction structure, namely PtSe 2 /Ge/Al 2 O 3 。
In this comparative example, a silicon dioxide, platinum film may be deposited using conventional techniques such as sputtering, electron beam deposition, and the like.
In this comparative example, the fabrication of the photodetector may be accomplished by fabricating the electrode using conventional techniques such as sputtering, electron beam deposition, spin coating, and the like.
The platinum diselenide thin film can be prepared by adopting a conventional preparation method, such as a chemical vapor deposition method (CVD), a thermal assisted conversion method (TAC), a molecular beam epitaxy Method (MBE), a chemical vapor transport method (CVT) and the like. Wherein the precursors which can be selected by the heat-assisted conversion method are a platinum film and selenium powder, the reaction temperature of the precursors is lower than 400 ℃, and the precursors react under the inert atmosphere to form PtSe 2 Thin film, the process is compatible with germanium-based CMOS processes.
For comparative example 1, the invention characterizes the performance of the prepared platinum diselenide thin film/germanium heterogeneous photodetector, and the characterization result is shown in fig. 6.
Fig. 6 is a graph comparing the photoelectric performance of the platinum diselenide/ultrathin insulating layer/germanium/backside insulating layer heterojunction photodetector of example 1 with the platinum diselenide/germanium/insulating layer heterojunction photodetector of comparative example 1 (zero bias); FIG. 6 (a) is an I-V diagram of two devices in the dark state; FIG. 6 (b) is an I-T diagram of two devices under different wavelength light source illumination; FIG. 6 (c) is a graph showing the response of two devices under different wavelengths of light; FIG. 6 (d) is a graph showing the specific detectivity of two devices under different wavelength light source;
comparing example 1 with comparative example 1, it can be seen that the addition of an ultra-thin insulating layer (this example is only illustrated with alumina as the insulating layer material, but is equally applicable to other insulating layer materials) to the heterojunction (example 1) can greatly reduce the dark current and improve the responsivity and the specific detectivity. In embodiment 1, the ultra-thin insulating layer can increase the PN junction barrier to block the diffusion of the majority carriers to reduce the dark current, thereby achieving the purpose of improving the on-off ratio, responsivity and specific detectivity.
The present invention compares the performance of the associated photodetectors as summarized in table 1. Table 1 shows a summary of the device performance of example 1, example 2, example 3, example 4 and comparative example 1 and other reported photodetector performance parameters for similar device structures.
TABLE 1
Note: the literature in table 1 is as follows:
[1]Y.Lu,Y.Wang,C.Xu,C.Xie,W.Li,J.Ding,W.Zhou,Z.Qin,X.Shen,L.-B.Luo,Nanoscale 2021,13,7606.
[2]H.Xiao,T.Liang,J.Xu,M.Xu,Adv.Opt.Mater.2021,9,2100664.
[3]L.Liu,X.Cao,L.Peng,S.C.Bodepudi,S.Wu,W.Fang,J.Liu,Y.Xiao,X.Wang,Z.Di,presented at 2021IEEE International Electron Devices Meeting(IEDM),2021.
[4]V.Dhyani,M.Das,W.Uddin,P.K.Muduli,S.Das,Appl.Phys.Lett.2019,114,121101.
[5]C.H.Lee,Y.Park,S.Youn,M.J.Yeom,H.S.Kum,J.Chang,J.Heo,G.Yoo,Adv.Funct.Mater.2022,32,2107992.
as can be obtained from fig. 4 (a) of example 1, the device has a distinct rectification characteristic, and an open-circuit voltage of 0.11V and a short-circuit current of 1.3mA are obtained under the irradiation of a light source of 1550 nm; as can be seen from fig. 4 (b), the higher the incident light power density is, the higher the photocurrent of the device is. This indicates that under higher power density incident light illumination, at PtSe 2 /Al 2 O 3 More photogenerated carriers are generated at the/Ge interface and separated by the built-in electric field,thereby producing a higher photocurrent; as can be seen from fig. 4 (c), the device can rapidly respond to the incident light signal with rise/fall times of 94.4 μ s and 67.1 μ s, respectively; from FIG. 4 (d), it can be obtained that under the irradiation of 1550nm light source, ptSe is obtained 2 /Al 2 O 3 The responsivity and specific detectivity of the/Ge photoelectric detector can be respectively as high as 4.24A/W and 4.47 multiplied by 10 9 Jones, with increasing incident light power density, recombines more photogenerated carriers and the responsivity and specific detectivity of the device will also gradually decrease.
As can be seen from fig. 5 of embodiment 1, the higher the incident light power density is, the higher the photocurrent of the device is. The PtSe 2 /Al 2 O 3 the/Ge device also has periodic and repeatable light response characteristics to light sources with wavelengths of 375nm,532nm and 940nm, so that the response range of the device can include the wavelengths of 375nm to 1550 nm.
By comparing example 1 with comparative example 1 of fig. 6, it can be seen that PtSe with ultra-thin alumina passivation layer 2 the/Ge device shows more excellent rectification characteristics; ptSe under the irradiation of the same incident light power density with different wavelengths 2 /Al 2 O 3 Photocurrent ratio PtSe of/Ge photoelectric detector 2 The size of the Ge device is much larger, and the dark-state current is obviously inhibited; ptSe 2 /Al 2 O 3 The responsivities of the/Ge photoelectric detector to the illumination of 375nm,532nm,940nm and 1550nm are respectively 0.31A/W,1.36A/W,1.80A/W and 4.24A/W, while the responsivity of the PtSe photoelectric detector is 0.31A/W,1.36A/W,1.80A/W and 4.24A/W 2 The responsivities of the/Ge photoelectric detector to illumination at 375nm,532nm,940nm and 1550nm are only 0.005A/W,0.083A/W,0.450A/W and 1.11A/W respectively; ptSe 2 /Al 2 O 3 The specific detectivity of the/Ge photoelectric detector for the illumination of 375nm,532nm,940nm and 1550nm is 3.23 multiplied by 10 8 Jones，1.43×10 9 Jones，1.90×10 9 Jones and 4.47X 10 9 Jones, and PtSe 2 The responsivity of the/Ge photoelectric detector to the illumination of 375nm,532nm,940nm and 1550nm is only 5.41 multiplied by 10 6 Jones，8.79×10 7 Jones，4.74×10 8 Jones and 1.17X 10 9 Jones。
As can be seen by comparing Table 1 with the prior art, the present invention is based on PtSe 2 Ultra-thin layer of Al 2 O 3 The overall performance (responsivity, specific detectivity, etc.) ratio of/Ge photodetectors is based on PtSe 2 /Ge、WSe 2 /Ge、MoSe 2 Ge and MAG/Al 2 O 3 The performance of the/Ge photoelectric detector is good.
Due to the limitation of test conditions, the invention only adopts 375nm,532nm,940nm and 1550nm lasers to test the photoelectric response of the photoelectric detector based on the platinum diselenide thin film/insulating layer/germanium heterojunction, but does not exclude the response of the photoelectric detector in other spectral ranges.
The excellent parameters obtained from the above characterization indicate that: the platinum diselenide thin film/insulating layer/germanium heterogeneous photoelectric detector has high responsivity, specific detectivity and on-off ratio, high response speed, wide response range and extremely low dark current, and can meet the requirements of practical application.
In the embodiment of the invention, the thickness of the platinum diselenide is in the range of 0.7-50.0nm, and the semiconductor characteristics (energy band structures) of the thin films with different thicknesses are different, so that the response to light with different wavelengths is different.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the invention herein disclosed is not limited to the particular combination of features described above, but also encompasses other embodiments in which any combination of the features described above or equivalent features thereof can be combined without departing from the novel concept of the present invention.
Claims (10)
1. A heterojunction based on platinum diselenide and germanium, which is characterized by comprising a germanium layer, a platinum diselenide layer, an ultrathin insulating layer and a back insulating layer;
the ultrathin insulating layer is arranged above the germanium layer;
the platinum diselenide layer is positioned above the ultrathin insulating layer;
the back side insulating layer is under the germanium layer.
2. A heterojunction as claimed in claim 1, wherein said ultra-thin insulating layer has a thickness of 1-6nm.
3. The heterojunction as claimed in claim 1 wherein the thickness of the platinum diselenide layer is from 0.7nm to 50.0nm.
4. A heterostructure as claimed in claim 1, wherein the material of the ultra-thin insulating layer and the back side insulating layer comprises any one or more of silicon dioxide, aluminium oxide, graphene oxide, boron nitride and insulating polymer.
5. A preparation method of a heterojunction based on platinum diselenide and germanium is characterized by comprising the following steps:
manufacturing an ultrathin insulating layer above the germanium layer to form an ultrathin insulating layer/germanium structure;
manufacturing a back insulating layer below the germanium layer to form an ultrathin insulating layer/germanium/back insulating layer structure;
and preparing a platinum diselenide film above the ultrathin insulating layer to form a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure.
6. Method for the preparation of a heterojunction as claimed in claim 5, characterized in that it comprises in particular the following steps:
(1) Preparing an insulating layer on a germanium substrate;
(2) Setting a working area on the insulating layer/germanium substrate, wherein the working area is used for constructing a platinum diselenide/ultrathin insulating layer/germanium heterojunction;
(3) Etching the insulating layer of the working area by using an etching solution to expose germanium, wherein the insulating layer which is not etched outside the working area can isolate the working area;
(4) Preparing an ultrathin insulating layer in the working area to form an ultrathin insulating layer/germanium structure;
(5) Preparing a back insulating layer on the back of the germanium substrate to form an ultrathin insulating layer/germanium/back insulating layer structure;
(6) And preparing a platinum diselenide film in the working area to form a platinum diselenide/ultrathin insulating layer/germanium/back insulating layer heterojunction structure.
7. A photodetector based on a heterojunction of platinum diselenide and germanium, characterized in that it comprises a heterojunction as claimed in any one of claims 1 to 4 and an electrode in electrical contact with said heterojunction;
the electrodes in electrical contact with the heterogeneous solid layer include an electrode in electrical contact with the platinum diselenide layer and an electrode in electrical contact with the germanium layer.
8. The photodetector of claim 7, wherein the electrode is selected from a metallic material or a non-metallic conductor material.
9. The photodetector of claim 8, wherein the non-metallic conductor material is selected from graphene, PEDOT: PSS.
10. A preparation method of a photoelectric detector based on a heterojunction of platinum diselenide and germanium is characterized by comprising the following steps:
preparation of platinum diselenide and germanium based heterojunctions: respectively manufacturing an ultrathin insulating layer and a back insulating layer above and below the germanium layer, and preparing a platinum diselenide film on the ultrathin insulating layer to form a platinum diselenide/ultrathin insulating layer/germanium heterojunction structure;
preparing a photoelectric detector based on a heterojunction of platinum diselenide and germanium: and preparing electrodes on the platinum diselenide layer and the germanium layer based on the obtained heterojunction of the platinum diselenide and the germanium to complete the preparation of the photoelectric detector.
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