CN110911518A - III-nitride semiconductor avalanche photodetector and preparation method thereof - Google Patents
III-nitride semiconductor avalanche photodetector and preparation method thereof Download PDFInfo
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- H01L31/03048—Inorganic materials including, apart from doping materials or other impurities, only AIIIBV compounds including ternary or quaternary compounds, e.g. GaAlAs, InGaAs, InGaAsP comprising a nitride compounds, e.g. InGaN
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- H01L31/1848—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP comprising ternary or quaternary compounds, e.g. Ga Al As, In Ga As P comprising nitride compounds, e.g. InGaN, InGaAlN
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Abstract
The invention discloses a III-group nitride semiconductor avalanche photodetector and a preparation method thereof, wherein the III-group nitride semiconductor avalanche photodetector comprises an active layer, and the active layer sequentially comprises heavily doped n-type Al according to the growth sequence from bottom to topxGa1‑xN ohmic contact layer unintentionally doped with AlyGa1‑yN and p-type layers; the p-type layer comprises p-type Al with higher doping concentration from top to bottomyGa1‑yN layer and p-type Al with lower doping concentrationyGa1‑yN layer of p-type Al with lower doping concentrationyGa1‑yThe N layer is of a concave structure with a thin center and a thick edge, and the p-type Al with higher doping concentrationyGa1‑yThe N layer is p-type Al with lower doping concentrationyGa1‑yN layers of matched convex with thick center and thin edgeAnd (4) a mold structure. Compared with the prior art, the p-type layer can limit a high electric field in the center of the mesa-shaped device, the electric field intensity is reduced at the edge of the mesa-shaped structure, the problem of early breakdown caused by overhigh edge electric field is solved, and the p-type layer has the effects of reducing surface recombination current and improving the working reliability of the device.
Description
Technical Field
The invention relates to the technical field of photodetectors, in particular to a III-nitride semiconductor avalanche photodetector and a preparation method thereof.
Background
The ultraviolet photoelectric detector based on the ternary III-nitride semiconductor AlGaN has wide attention of people because the ultraviolet photoelectric detector can realize intrinsic visible light blind (280-400 nm) and solar blind ultraviolet (220-280 nm) detection, and has wide application prospect in the fields of high-voltage corona discharge detection, flame detection, environment monitoring, astronomical physics and the like. In most uv detection applications, since the uv signal is typically very weak, uv photodetectors are required to have low dark current, high quantum efficiency, and high internal gain. Avalanche photodiodes have the advantages of high photocurrent gain, high response speed, low noise, etc., and are one of the most promising types of devices for high-sensitivity ultraviolet detection.
Avalanche Photodetectors (APDs) operate by triggering the avalanche effect with the internal high electric field of the multiplication region. However, for the generally adopted quasi-vertical mesa structure, the surface of the mesa edge of the device has an excessively high fringe electric field due to a surface state formed by vacancies, impurities, intrinsic defects, or the like introduced by dry etching, and therefore, it is a very important link to take measures to suppress the fringe electric field of the device. Recently, a relatively representative scheme is (1) forming a multi-step edge structure by etching a plurality of times, (2) forming a mesa structure whose edge is inclined by etching, and (3) forming a guard ring by performing ion implantation at the edge of the mesa structure. The function of the device is to locate the high electric field in the center of the device and reduce the edge electric field intensity. However, the use of the multi-step and inclined step structure reduces the effective light absorption area, while the use of ion implantation to form the guard ring requires expensive ion implantation equipment, and the difficulty of process control of the concentration and depth of ion implantation is large. Therefore, development of a new fringe electric field control technology is required.
Disclosure of Invention
The present invention is directed to overcoming at least one of the above-mentioned deficiencies in the prior art and providing a III-nitride semiconductor avalanche photodetector with a low fringe electric field that effectively avoids the problem of premature breakdown due to an excessively high fringe electric field on the device, and at the same time, with a low recombination dark current on the device surface and high reliability.
Another object of the present invention is to provide a method for fabricating a group III nitride semiconductor avalanche photodetector, which can reduce the fringe electric field by adjusting the p-type doping profile through secondary epitaxial growth.
The technical scheme adopted by the invention is as follows:
the avalanche photodetector comprises an active layer, wherein the active layer sequentially comprises heavily doped n-type Al according to the growth sequence from bottom to topxGa1-xN ohmic contact layer unintentionally doped with AlyGa1-yAn N layer and a p-type layer; the p-type layer comprises p-type Al with higher doping concentration from top to bottomyGa1-yN layer and p-type Al with lower doping concentrationyGa1-yN layer of p-type Al with lower doping concentrationyGa1-yThe N layer is of a concave structure with a thin center and a thick edge, and the p-type Al with higher doping concentrationyGa1-yThe N layer is p-type Al with lower doping concentrationyGa1-yN layers of matched convex structures with thick centers and thin edges.
The p-type layer comprises p-type Al with different thicknesses and higher doping concentrationyGa1-yN layer and low doping concentration p-type AlyGa1-yAnd N layers. Wherein, the center of the device is highly doped with p-type AlyGa1-yThe thicker part of N defines a high electric field area, and the edge of the N is doped with p-type AlyGa1-yThe thicker portion of N acts as a guard ring, which reduces the fringe field of the mesa. The advantage of this structure of the P-type layer is that it can confine the high electric field to the center of the mesa device, i.e., to the lower doping concentration of P-type AlyGa1-yN layers of concave structures with thin centers and thick edges; at the edge of the mesa structure, the electric field intensity is reduced, so that the problem of early breakdown caused by overhigh edge electric field is solved; meanwhile, the surface recombination dark current of the device is reduced, and the reliability of the device is improved.
The P-type layer can be used in a PIN structure III-nitride semiconductor avalanche photodetector, a PIN structure derived PININ and other absorption and multiplication layer structure semiconductor avalanche photodetectors or a P-type layer inverted NIP structure, and specifically, the P-type layer inverted NIP structure refers to an N-type contact layer with high and low doping distribution as a top layer.
Furthermore, the total thickness of the p-type layer is 50-200 nm.
Further, the p-type Al with lower doping concentrationyGa1-yN layer and p-type Al with higher doping concentrationyGa1-yThe hole concentration of the N layer is p3And p4，p3、p4The following relationship is satisfied: p is a radical of3<p4. In particular, the p-type Al with higher doping concentrationyGa1-yHole concentration p of N layer4At 5X 1017～1×1019cm-3While the lower doping concentration of p-type AlyGa1-yHole concentration p of N layer3At 1X 1017～8×1017cm-3Meanwhile, the secondary epitaxial structure with high and low doping concentration distribution can reduce the fringe electric field of the device.
Further, the p-type Al with lower doping concentrationyGa1-yN layer and p-type Al with higher doping concentrationyGa1-yThe N layers satisfy the following relationship:
(1) the p-type Al with lower doping concentrationyGa1-yThe thickness of the center of the N layer is 10-50 nm, the thickness of the edge is 50-150 nm, and the width of the edge is more than or equal to 0.5 mu m;
(2) the p-type Al with higher doping concentrationyGa1-yThe thickness of the center of the N layer is 40-150 nm, the thickness of the edge is 10-120 nm, and the width of the edge is more than or equal to 0.5 μm.
According to the invention, by innovatively designing the doping concentration distribution and thickness of the p-type layer, the beneficial effects of reducing the fringe electric field, preventing breakdown in advance and improving the reliability of the device are achieved.
Further, the p-type Al with lower doping concentrationyGa1-yAl component z of N layer30 to 0.65, hole concentration p3＝1×1017～8×1017cm-3(ii) a The p-type Al with higher doping concentrationyGa1-yAl component z of N layer40 to 0.65, hole concentration p4＝5×1017～1×1019cm-3。
Further, the unintentional doping of AlyGa1-yThe thickness of the N layer is 100-300 nm, the Al component y is 0-0.65, and the electron concentration is 1 × 1016～2×1017cm-3. The unintentional doping with AlyGa1-yThe N layer has the function of utilizing the high electric field intensity in the N layer to enable photo-generated carriers entering the N layer to generate collision ionization, triggering an avalanche effect and generating avalanche gain.
Further, the heavily doped n-type AlxGa1-xThe thickness of the N ohmic contact layer is 0.3-1 μm; the Al component range x is 0-0.8, and the electron concentration in the layer is 5 × 1017～5×1018cm-3。
Further, the Al components of the heavily doped n-type AlxGa1-xN ohmic contact layer and the unintentionally doped AlyGa1-yN satisfy x ≧ y. Due to the heavily doped N-type AlxGa1-xAn N-type ohmic contact layer serving as both an N-type ohmic contact electrode layer and a main incident window layer when Al component x>y, which can act as a window layer for light incident on the substrate side.
Another object of the present invention is to provide a method for manufacturing the group III nitride semiconductor avalanche photodetector, which comprises the following steps: after the low-doped p-type layer is epitaxially grown, a mask is formed through photoetching, low-damage dry etching is carried out on the low-doped p-type layer at the central part of the device of the planned manufacturing platform type structure region, etching surface damage recovery processing is carried out, and then a layer of high-doped p-type layer is epitaxially grown for the second time on the basis, so that a p-type layer structure with the thick central high-doping layer and the thick edge low-doping layer of the device is formed.
The invention adopts a secondary epitaxial p-type layer to distribute a p-type doping layer in a subarea way, namely, a low-doped p-type layer is epitaxially grown firstly, then the central part of the low-doped p-type layer in the area of the avalanche photodetector with the planned table-type structure is etched, the thickness of the central area is reduced, after the etching surface is treated, a high-doped p-type layer is epitaxially grown again, and the structure that the low-doped p-type layer at the edge of the composite p-type layer of the table-type device is thick and the high-doped p-type layer is thin and the low-doped p-type layer in the central area is thin and the high-doped. In the growth process, a mask is not needed, and the growth mode of selective area epitaxy is avoided, so that the adverse factor that the film cannot be effectively formed due to low mobility of Al atoms on the upper surface of the mask in the selective area epitaxy AlGaN process is avoided. By adopting the technical scheme, the fringe electric field of the device can be effectively reduced, advanced breakdown caused by overhigh fringe electric field of the device is prevented, the surface recombination dark current of the device is reduced, and the reliability of the device is improved.
Further, the epitaxial growth employs a metal organic chemical vapor deposition epitaxial epitaxy (MOCVD) or a Molecular Beam Epitaxy (MBE).
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a PIN structure-based III-group nitride semiconductor avalanche photodetector, wherein a p-type layer comprises p-type Al with different thicknesses and high doping concentrationyGa1-yN layer and low doping concentration p-type AlyGa1-yThe N layer, the structure of the P type layer has the advantage of limiting a high electric field in the center of the mesa device, namely, in the range of the concave structure with the thin center and the thick edge of the P type AlyGa1-yN layer with lower doping concentration; and at the edge of the mesa structure, the electric field intensity is reduced, so that the problem of early breakdown caused by overhigh edge electric field is solved. The P-type layer structure can be used in a PIN structure III-nitride semiconductor avalanche photodetector, and can also be used in a PIN structure derived PININ and other absorption and multiplication layer structure semiconductor avalanche photodetectors or a P-type layer inverted NIP structure. The preparation method provided by the invention adopts the secondary epitaxial p-type layer, and in the growth process, the technical scheme does not need to use a mask, so that the growth mode of selective area epitaxy is avoided, and the adverse factor that the film cannot be effectively formed due to low mobility of Al atoms on the surface of the mask in the selective area epitaxial AlGaN process is avoided. In conclusion, the technology provided by the invention is adoptedThe technical scheme can effectively reduce the edge electric field of the device, prevent the device from being broken down in advance due to overhigh edge electric field, reduce the surface recombination dark current of the device and improve the reliability of the device.
Drawings
Fig. 1 is a schematic structural diagram of embodiment 1 of the present invention.
Fig. 2 is a graph showing the comparison result of the lateral electric field at the highest electric field of the device using the high and low doped P-type layer and the device using the uniformly doped P-type layer.
Fig. 3 is a schematic structural diagram of embodiment 2 of the present invention.
FIG. 4 is a schematic structural diagram of embodiment 3 of the present invention
Detailed Description
The drawings are only for purposes of illustration and are not to be construed as limiting the invention. For a better understanding of the following embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
Example 1
As shown in fig. 1, the present embodiment provides a group III nitride semiconductor avalanche photodetector, specifically an AlGaN semiconductor avalanche photodetector based on a PIN structure, and specifically includes: heavily doped n-type Al with thickness of 0.4 mu mxGa1- xN ohmic contact layer 101, 160nm thick unintentionally doped AlyGa1-yAn N layer 102 and a 100nm thick p-type layer; wherein n-type Al is heavily dopedxGa1-xThe Al composition x of the N ohmic contact layer 101 was 0.6 and the electron concentration was 2 × 1018cm-3Said unintentional doping with AlyGa1-yThe Al composition y of the N layer 102 was 0.4, and the electron concentration was 6 × 1016cm-3。
Furthermore, the p-type layer comprises p-type Al with higher doping concentration which are sequentially stacked from top to bottomyGa1-yN layer 104, p-type Al with lower doping concentrationyGa1-yThe specific parameters of the N layer 103 are as follows:
(1) the low doping concentrationDegree n-type AlyGa1-yThe N layer 103 had a center thickness of 40nm, an edge thickness of 80nm, an edge width of 2 μm, and an electron concentration of 2X 1017cm-3The Al component y is 40%;
(2) the p-type Al with high doping concentrationyGa1-yThe N layer 104 had a central thickness of 60nm, an edge thickness of 20nm, an edge width of 2 μm, and a hole concentration of 4X 1018cm-3And the Al component y is 40%.
Specifically, the higher doping concentration p-type Al in this embodimentyGa1-yThe edge of N layer 104 is slightly higher than the center of the device.
The preparation method of the AlGaN semiconductor avalanche photodetector based on the PIN structure specifically comprises the step of growing p-type Al with lower doping concentrationyGa1-yAfter the N layer 103 is formed, a mask is formed by photolithography, and p-type Al with a lower doping concentration is doped in the central portionyGa1-yThe N layer is subjected to low-damage dry etching, the damage of the etching surface is recovered, and then a layer of p-type Al with higher doping concentration is epitaxially grown for the second time on the basisyGa1-yAnd an N layer 104, thereby forming a p-type layer structure with the thickness of a high doping layer in the center of the device and the thickness of a low doping layer at the edge of the device.
Further, the epitaxial growth adopts a metal organic chemical vapor deposition epitaxial epitaxy (MOCVD).
In this embodiment, the p-type Al with high doping concentration is usedyGa1-yN layer 104, low doping concentration p-type AlyGa1-yThe hole concentration of the p-type layer formed by the N layer 103 presents high-low type doping distribution, and compared with a p-type layer structure with uniform doping concentration, the p-type layer structure can reduce the fringe electric field of a device, prevent early breakdown and reduce dark current, thereby realizing the preparation of the high-performance AlGaN ultraviolet avalanche photodetector with low noise, high gain and high quantum efficiency. A comparison graph of the lateral electric field of the highest electric field region of the corresponding device of the high-low doped P-type layer and the conventional uniformly doped P-type layer in this embodiment is shown in fig. 2, and under the condition that the central electric field of the device is approximately the same, it can be seen that the electric field introduced into the high-low doped P-type layer device is larger than that of the uniformly doped P-type layer device at the position 40 microns at the edge of the deviceAnd decreases.
Example 2
As shown in fig. 3, the present embodiment provides a group III nitride semiconductor avalanche photodetector, and in particular, an AlGaN semiconductor avalanche photodetector based on a PIN structure derived pincin absorption-multiplication separation structure, including: heavily doped n-type Al with thickness of 0.4 mu mxGa1-xN ohmic contact layer 301, 0.18 μm thick unintentionally doped AlyGa1-yN absorption layer 302, 60nm thick AlyGa1-yN charge layer 303, 130nm thick unintentionally doped AlyGa1-yAn N-fold layer 304 and a 100nm thick p-type layer; wherein, the Al component x is 0.6, y is 0.4, the heavily doped n-type AlxGa1-xThe electron concentration of the N ohmic contact layer 301 was 2X 1018cm-3Said unintentional doping with AlyGa1-yThe electron concentration of the N absorption layer 302 is 6X 1016cm-3The electron concentration of the charge layer 303 is 1X 1018cm-3The electron concentration of the multiplication layer 304 is 6X 1016cm-3。
Furthermore, the p-type layer comprises p-type Al with higher doping concentration which are sequentially stacked from top to bottomyGa1-yN layer 306, p-type Al with lower doping concentrationyGa1-yN layers 305, the specific parameters are as follows:
(1) low doping concentration p-type AlyGa1-yThe N layer 305 had a center thickness of 40nm, an edge thickness of 80nm, an edge width of 2 μm, and an electron concentration of 2X 1017cm-3The Al component y is 0.40;
(2) high doping concentration p-type AlyGa1-yThe N layer 306 had a central thickness of 60nm, an edge thickness of 20nm, an edge width of 2 μm, and a hole concentration of 4X 1018cm-3And the Al component y is 0.40.
Specifically, the higher doping concentration p-type Al in this embodimentyGa1-yThe edge of the N layer 306 is slightly higher than the center of the device.
The preparation method of the AlGaN semiconductor avalanche photodetector based on the PIN structure is characterized in that the growth is lowP-type Al with doping concentrationyGa1-yAfter the N layer 303 is formed, a mask is formed by photolithography, and p-type Al with a lower doping concentration is doped in the central portionyGa1-yThe N layer is subjected to low-damage dry etching, the damage of the etching surface is recovered, and then a layer of p-type Al with higher doping concentration is epitaxially grown for the second time on the basisyGa1-yAnd an N layer 304, thereby forming a p-type layer structure with the thickness of a high doping layer in the center of the device and the thickness of a low doping layer at the edge of the device.
Further, the epitaxial growth is performed by Molecular Beam Epitaxy (MBE).
In this embodiment, the p-type Al with high doping concentration is usedyGa1-yN layer 306, low doping concentration p-type AlyGa1-yThe hole concentration of the p-type layer formed by the N layer 305 is in high-low type doping distribution, and compared with a p-type layer structure with uniform doping concentration, the p-type layer structure can reduce the fringe electric field of a device, prevent early breakdown and reduce dark current, so that the preparation of the high-performance AlGaN ultraviolet avalanche photodetector with low noise, high gain and high quantum efficiency is realized.
Example 3
As shown in fig. 4, this embodiment is different from embodiment 1 in that P-type Al with higher doping concentration in the P-type layeryGa1-yThe thickness of the edges of the N layer 104 is the same as the thickness of the center of the device.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific embodiments of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention claims should be included in the protection scope of the present invention claims.
Claims (10)
1. The avalanche photodetector comprises an active layer, and is characterized in that the active layer sequentially comprises heavily doped n-type Al according to the growth sequence from bottom to topxGa1-xAn N-ohmic contact layer (101) unintentionally doped with AlyGa1-yAn N layer (102) and a p-type layer; the p-type layer is wrapped from top to bottomP-type Al with higher doping concentrationyGa1-yAn N layer (104) and a lower doping concentration of p-type AlyGa1-yAn N layer (103) of p-type Al with lower doping concentrationyGa1-yThe N layer is of a concave structure with a thin center and a thick edge, and the p-type Al with higher doping concentrationyGa1-yThe N layer (104) is p-type Al with the lower doping concentrationyGa1-yThe N layers (103) are matched with a convex structure with thick center and thin edge.
2. The avalanche photodetector of claim 1, wherein the total thickness of the p-type layer is 50 to 200 nm.
3. The ill-nitride semiconductor avalanche photodetector of claim 2, wherein the lower doping concentration of p-type AlyGa1-yN layer (103) and p-type Al with higher doping concentrationyGa1-yThe N layers (104) each have a hole concentration of p3And p4，p3、p4The following relationship is satisfied: p is a radical of3<p4。
4. A group III nitride semiconductor avalanche photodetector according to any one of claims 1 to 3, wherein the lower doping concentration of p-type AlyGa1-yN layer (103) and p-type Al with higher doping concentrationyGa1-yThe N layers (104) satisfy the following relationship:
(1) the p-type Al with lower doping concentrationyGa1-yThe thickness of the center of the N layer (103) is 10-50 nm, the thickness of the edge is 50-150 nm, and the width of the edge is more than or equal to 0.5 mu m;
(2) the p-type Al with higher doping concentrationyGa1-yThe thickness of the center of the N layer (104) is 40-150 nm, the thickness of the edge is 10-120 nm, and the width of the edge is more than or equal to 0.5 μm.
5. The III-nitride semiconductor avalanche photodetector of claim 4, wherein the avalanche photodetector is characterized byP-type Al of said lower doping concentrationyGa1-yAl component z of N layer (103)30 to 0.65, hole concentration p3＝1×1017～8×1017cm-3(ii) a The p-type Al with higher doping concentrationyGa1-yAl component z of N layer (104)40 to 0.65, hole concentration p4＝5×1017～1×1019cm-3。
6. A group III nitride semiconductor avalanche photodetector according to any one of claims 1 to 3, wherein the unintentional doping with Al is carried outyGa1-yThe thickness of the N layer (102) is 100-300 nm, the Al component y is 0-0.65, and the electron concentration is 1 x 1016～2×1017cm-3。
7. The III-nitride semiconductor avalanche photodetector as claimed in any one of claims 1 to 3, wherein the heavily doped n-type AlxGa1-xThe thickness of the N ohmic contact layer (101) is 0.3-1 μm; the Al component range x is 0-0.8, and the electron concentration in the layer is 5 × 1017～5×1018cm-3。
8. The ill-nitride semiconductor avalanche photodetector of claim 7, wherein the Al composition of the heavily doped n-type AlxGa1-xN ohmic contact layer (101) and the unintentionally doped AlyGa1-yN (102) satisfies x ≧ y.
9. The method for preparing a group III nitride semiconductor avalanche photodetector as claimed in any one of claims 1 to 8, wherein after the low doped p-type layer is epitaxially grown, a mask is formed by photolithography, and thereafter the low doped p-type layer at the central portion of the device where the mesa structure region is planned to be fabricated is subjected to low damage dry etching to recover the damage on the etched surface, and then a high doped p-type layer is epitaxially grown twice on the basis of the low doped mask, thereby forming a p-type layer structure having a thick central high doped layer and a thick edge low doped layer.
10. The method of claim 9, wherein the epitaxial growth is performed by metal organic chemical vapor deposition epitaxial epitaxy (MOCVD) or Molecular Beam Epitaxy (MBE).
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