WO2006033516A1 - Photodiode having electrode structure for large optical signal receiving area - Google Patents

Photodiode having electrode structure for large optical signal receiving area Download PDF

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Publication number
WO2006033516A1
WO2006033516A1 PCT/KR2005/002084 KR2005002084W WO2006033516A1 WO 2006033516 A1 WO2006033516 A1 WO 2006033516A1 KR 2005002084 W KR2005002084 W KR 2005002084W WO 2006033516 A1 WO2006033516 A1 WO 2006033516A1
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Prior art keywords
electrode
receiving area
light receiving
photodiode
photodiode according
Prior art date
Application number
PCT/KR2005/002084
Other languages
French (fr)
Inventor
Han-Gwon Ryu
Seon-Ho Song
Za-Il Lhee
Bon-Jo Koo
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Ls Cable Ltd.
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Publication date
Application filed by Ls Cable Ltd. filed Critical Ls Cable Ltd.
Priority to JP2007533395A priority Critical patent/JP2008514025A/en
Publication of WO2006033516A1 publication Critical patent/WO2006033516A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/1443—Devices controlled by radiation with at least one potential jump or surface barrier
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0304—Inorganic materials including, apart from doping materials or other impurities, only AIIIBV compounds
    • H01L31/03046—Inorganic materials including, apart from doping materials or other impurities, only AIIIBV compounds including ternary or quaternary compounds, e.g. GaAlAs, InGaAs, InGaAsP
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier
    • H01L31/105—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier the potential barrier being of the PIN type
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/544—Solar cells from Group III-V materials

Definitions

  • the present invention relates to a photodiode, and more particularly to a photodiode having an electrode structure capable of configuring a large optical receiving area so as to increase quantity of received lights.
  • a photodiode has more quantity of received light as a light receiving area is greater, so it may support ore accurate data transmission operation and allows easy alignment when being coupled to an optical fiber.
  • FIG. 1 shows configuration of a general photodiode.
  • the photodiode includes an InP substrate 10, a light receiving area 11 formed on the substrate 10, and an electrode pad 12 Ohmic-contacted on the substrate 10 to be adjacent to the light receiving area 11.
  • an electron-hole pair is generated in correspondence to photons absorbed in the light receiving area 11, and ac ⁇ cordingly a carrier is transported to an external circuit through the electrode pad 12.
  • a current when an optical signal is not input namely a dark current
  • a Wien re- sponsivity of an output current corresponding to an input light should be high.
  • diode capacitance, parasitic capacitance and carrier transport time are also variables affecting on an operation speed of a photodiode.
  • a width W of a depletion layer is expressed as in the following Expression 2.
  • e is a dielectric constant
  • A is a junction area
  • V is a back bias voltage
  • V bi is a junction built-in voltage
  • q is an amount of charges
  • N E is a concentration of pure charge in the I layer.
  • FIG. 2 shows a photodiode having an electrode pad 12 formed on a SiO film and a ring-shaped metal electrode 13 formed along an edge of the light receiving area 11 so as to minimize a capacitance that became a problem when a light receiving area is increased to have a large caliber.
  • a parasitic capacitance may be minimized by transferring a current, generated in correspondence to an input optical signal, to an external circuit through the ring-shaped electrode 13 Ohmic-contacted with the light receiving area 11 and the electrode pad 12 connected to the ring-shaped electrode 13.
  • the present invention is designed in consideration of the above problems, and therefore it is an object of the invention to provide a photodiode having an electrode structure that may solve reflection problem occurring when being aligned to an optical fiber, minimize a capacitance and also reduce a transport time of a carrier.
  • the present invention provides a photodiode, which includes a light receiving area having a junction structure of a compound semiconductor for photoelectric conversion; a first electrode having a net structure Ohmic-contacted to a light input region on one side of the light receiving area; and a second electrode formed on the other side of the light receiving area in cor ⁇ respondence to the first electrode.
  • the net structure of the first electrode has a square pattern whose length and width are 30 to 50 ⁇ m.
  • the first electrode is composed of wire whose width is 1 to 4 ⁇ m.
  • the photodiode of the present invention may further include a ring-shaped electrode electrically connected to the first electrode and Ohmic-contacted along an edge of the light input region of the light receiving area.
  • the light receiving area may include a N-type InP substrate; a N-type InP buffer layer formed on the substrate; an InGaAs absorption layer formed on the buffer layer; and an InP layer formed on the absorption layer.
  • the photodiode of the present invention further includes a SiO insulation film formed on the InP layer around the light input region; a non-reflective film passivated on the SiO insulation film; and an electrode pad formed on the non- reflective film and connected to the first electrode.
  • the InGaAs absorption layer preferably has a thickness of 2.0 to 3.4 ⁇ m.
  • FIG. 1 is a plane view showing configuration of a conventional photodiode
  • FIG. 2 is a plane view showing another configuration of a conventional photodiode
  • FIG. 3 is a plane view showing configuration of a photodiode according to a preferred embodiment of the present invention.
  • FIG. 4 is a partially sectioned perspective view showing inner configuration of the photodiode according to the preferred embodiment of the present invention.
  • FIG. 5 is a graph showing a frequency response characteristic of the photodiode according to one embodiment of the present invention.
  • FIG. 6 shows a system configuration for measuring an impulse response of a photodiode
  • FIGs. 7 and 8 are plane views showing alignment positions when measuring an impulse response of a photodiode, according to comparative examples
  • FIGs. 9 and 10 are graphs showing impulse characteristics corresponding to optical alignment of the photodiode according to comparative examples.
  • FIGs. 11 and 12 are graphs showing frequency response features of the photodiode according to comparative examples. Best Mode for Carrying Out the Invention
  • FIG. 3 is a plane view showing configuration of a photodiode according to a preferred embodiment of the present invention
  • FIG. 4 is a partially sectioned perspective view thereof.
  • the photodiode includes a light receiving area 100 having a multi-layer junction structure of a compound semiconductor for photoelectric conversion, a first electrode 101 provided in a light input region of the light receiving area 100 and having a net structure, and a second electrode 107 formed on the other side of the light receiving area 100.
  • the first electrode 101 having a net structure is provided in the light input region of the light receiving area 100.
  • the net structure of the first electrode 101 is Ohmic- contacted to an upper portion of the light receiving area 100, and it is configured so that square wire patterns of 30 to 50 ⁇ m equal to or larger than a diameter of a general optical communication light are repeated.
  • the net-type wire pattern of the first electrode 101 preferably has a width of 1 to 4 ⁇ m so as not to affect on back reflectance of the photodiode and also not to give an effect on laser welding in the assembling procedure. More preferably, the wire of the first electrode 101 has a width of 2 to 4 ⁇ m.
  • the first electrode 101 is preferably composed to have multi layers of Ti/Pt/Au or Cr/ Au.
  • a ring-shaped electrode 102 may be further provided to an edge of the light input region of the light receiving area 100.
  • the ring-shaped electrode 102 Ohmic-contacted with the light receiving area 100 surrounds the edge of the net structure and also is electrically connected to the first electrode 101.
  • An electrode pad 103 electrically connected to the first electrode 101 and the ring- shaped electrode 102 to transport a carrier to an external circuit is provided around the light input region of the light receiving area 100.
  • a SiO insulation film 105 having a thickness of about l ⁇ m and a non-reflective film 106 made of Si N of about 1000 to 2000A passivated on the SiO insulation film 105 are provided around the light input region of the light receiving area 100.
  • the electrode pad 103 is formed on the non-reflective film 106 so as to minimize a parasitic capacity, and it is also preferably composed of multi layers of Ti/Pt/Au or Cr/ Au.
  • the light receiving area 100 has a compound semiconductor layer for generation of a carrier corresponding to an input light and a PN-junction structure for giving an electric field to transport the carrier to an electrode.
  • the light receiving area 100 may include a N-type InP substrate 108, a N-type InP buffer layer 109 formed on the substrate 108, an InGaAs absorption layer 110 formed on the buffer layer 109, and an InP layer 111 formed on the absorption layer 110.
  • the InP layer 111 is provided with a P-type InP region 104 formed by Zn diffusion, and the second electrode 107 corresponding to the first electrode 101 having a net structure is formed on the lower surface of the substrate 108.
  • the light receiving area 100 is not limited to the above configuration but may have various modifications such as a known PIN junction structure.
  • a frequency response giving greatest effects on the performance of the photodiode is limited by transmit time and capacitance for the absorption layer 110. That is to say, if thickness of the absorption layer 110 is increased too great, much transit time is consumed, while, if the thickness is decreased, capacitance is increased, thereby dete ⁇ riorating the frequency response characteristic.
  • the InGaAs absorption layer 110 preferably has a thickness of 2.0 to 3.4 ⁇ m
  • the light receiving area 100 preferably has a diameter of about 100 to 300 ⁇ m.
  • the light receiving area 100 preferably has a diameter of 100 to 150 ⁇ m.
  • the InP buffer layer 109, the InGaAs absorption layer 110, the InP layer 111 or the like of the light receiving area 100 may be formed subsequently by means of a film growth technique used in a common semiconductor manufacturing procedure.
  • the Zn diffusion region 104 in the upper portion of the InP layer 111 may be formed by means of a masking technique using common PECVD (Plasma Enhanced Chemical- Vapor Deposition), a photolithography technique, a lift-off technique, RTA (Rapid Thermal Annealing) or the like, and electrode structure such as the first electrode 101 having a net pattern, the ring-shaped electrode 102, the electrode pad 103 and the second electrode 107 may be prepared using a common E-beam deposition technique, a lift-off technique or wet etching.
  • InGaAs absorption layer 110, the InP layer 111 and an InGaAs capping layer (not shown) as a protective film are formed by means of growth using MOCVD, the InGaAs capping layer having a thickness of 0.1 ⁇ m is removed using a sulphuric acid etching solution, and a Si N film is deposited using a PECVD device to make a mask
  • a PR (Photo Resist) pattern for Zn diffusion is made on the Si N film by means of photolithography, and then Si N exposed by the PR pattern is etched using BOE (Buffered Oxide Etchant) solution.
  • BOE Borered Oxide Etchant
  • the lift-off process is executed for the wafer so that Zn P and PN are all removed with leaving a part of Zn P for Zn diffusion.
  • the lift-off process is executed in a way that the PR is melt using acetone solution or the like so that the PR and Zn P deposited on the PR are separated from the substrate.
  • the wafer on which SiO is capped is put into a RTA chamber under nitrogen environments and then Zn-RTA diffusion is executed for 4 minutes at 55O 0 C. After the diffusion process is completed, the SiO capping layer is removed by means of BOE, and then Zn P in a light receiving area remained after diffusion is removed using a nitrogen etching solution.
  • a PECVD device is used to deposit a SiO insulation layer in a thickness of l ⁇ m on the upper surface of the wafer, and then SiO in a region where Zn is diffused is removed using photolithography and BOE solution.
  • the non-reflective film (Si N ) 106 is formed by means of PECVD, and then a P-metal electrode, which is the first electrode having a net pattern, is formed using the photolithography and lift-off processes.
  • the P-metal electrode is formed in a way that, as for the wafer on which a PR pattern is formed through pho ⁇ tolithography, Ti/Pt/Au is deposited in a high vacuum of 1 10 Torr in a thickness of 400/600/1200 by using an E-beam evaporator, and then the metal film on an un ⁇ necessary area is removed by means of the lift-off process, followed by executing Ohmic contact annealing in the RTA chamber.
  • an electrode pad is formed at one side on the SiO insulation layer adjacent to the P-metal electrode.
  • a lapping process is executed for the back surface of the wafer to make a thickness of lOO ⁇ m, then Ti/Pt/Au adopted as a N-metal is deposited in a thickness of 400/600/3000A and then Ohmic contact annealing is again executed in
  • N-metal which is the second electrode corresponding to the P-metal having a net structure, is formed.
  • InGaAs absorption layer has a thickness of 2.0 ⁇ m and which includes an electrode having a net structure and an electrode pad was fabricated. [60] After measuring a frequency response speed of the photodiode of this embodiment, it was found that a frequency corresponding to 3dB bandwidth was 0.58 GHz when V R
  • InGaAs absorption layer has a thickness of 3.4 ⁇ m and which includes only an electrode pad directly formed on the InP substrate was fabricated (see FIG. 1).
  • InGaAs absorption layer has a thickness of 3.4 ⁇ m and which includes a ring-shaped electrode and an electrode pad formed on the SiO film was fabricated (see FIG. 2).
  • InGaAs absorption layer has a thickness of 2.0 ⁇ m and which includes only an electrode pad directly formed on the InP substrate was fabricated (see FIG. 1).
  • InGaAs absorption layer has a thickness of 2.0 ⁇ m and which includes a ring-shaped electrode and an electrode pad formed on the SiO film was fabricated (see FIG. 2).
  • the photodiode provided with an electrode having a net structure in the light receiving area shows an improved carrier transport characteristic, thereby capable of improving a frequency response characteristic corresponding to 3dB bandwidth rather than the con ⁇ ventional photodiode having only the ring-shaped electrode.
  • optical Sub Assembly it is possible to reduce a process time for optical fiber alignment, increase an allowable limit for alignment accuracy during the laser welding process owing to the large light receiving area, and also enable manual alignment in a pressuring manner.
  • the photodiode of the present invention may be useful as a photodiode for monitors and for receiving an optical signal of 155 Mbps to 2.5 Gbps.

Abstract

Disclosed is structure of a photodiode, which is capable of making a light receiving area get a large caliber. The photodiode includes a light receiving area having a junction structure of a compound semiconductor for photoelectric conversion; a first electrode having a net structure Ohmic-contacted to a light input region on one side of the light receiving area; and a second electrode formed on the other side of the light receiving area in correspondence to the first electrode.

Description

Description
PHOTODIODE HAVING ELECTRODE STRUCTURE FOR LARGE OPTICAL SIGNAL RECEIVING AREA
Technical Field
[1] The present invention relates to a photodiode, and more particularly to a photodiode having an electrode structure capable of configuring a large optical receiving area so as to increase quantity of received lights. Background Art
[2] A photodiode has more quantity of received light as a light receiving area is greater, so it may support ore accurate data transmission operation and allows easy alignment when being coupled to an optical fiber.
[3] However, when a light receiving area is enlarged, transit time and carrier transport time of the photodiode are elongated, so an operation speed becomes late and also a frequency response speed, a most essential electric feature of a photodiode, becomes late.
[4] FIG. 1 shows configuration of a general photodiode. Referring to FIG. 1, the photodiode includes an InP substrate 10, a light receiving area 11 formed on the substrate 10, and an electrode pad 12 Ohmic-contacted on the substrate 10 to be adjacent to the light receiving area 11. In this connection, an electron-hole pair is generated in correspondence to photons absorbed in the light receiving area 11, and ac¬ cordingly a carrier is transported to an external circuit through the electrode pad 12.
[5] In the photodiode configured as above, when light is input to InP, a hole is formed in a valence band and an electron is generated in a conductive band due to pho¬ toelectric effects by which electrons in the valence band are excited to the conduction band, so an electron-hole pair is generated. Accordingly, a carrier is moved to an electrode by means of an electric field provided by a PN-junction structure, and is then transported to an external circuit. In particular, recently, researches for a PIN photodiode in which an I layer, namely an intrinsic semiconductor layer, is interposed into the PN-junction structure are vigorously carried out.
[6] Generally, in order that a photodiode detects an optical signal better, a current when an optical signal is not input, namely a dark current, should be low, and a Wien re- sponsivity of an output current corresponding to an input light should be high. In addition, diode capacitance, parasitic capacitance and carrier transport time are also variables affecting on an operation speed of a photodiode.
[7] In case of a general flat PIN photodiode, if a light receiving area is enlarged, a diode capacitance C is increased by the following Expression 1 to increase a total ca- pacitance of an element, so an operation speed and a frequency response time are lowered. [8]
[9] Expression 1
[10]
A
C = Ξ i W
[H]
[12] In the above Expression 1, a width W of a depletion layer is expressed as in the following Expression 2. Here, e is a dielectric constant, A is a junction area, V is a back bias voltage, V bi is a junction built-in voltage, q is an amount of charges, and N E is a concentration of pure charge in the I layer. [13]
[14] Expression 2
[15]
Figure imgf000003_0001
[16]
[17] FIG. 2 shows a photodiode having an electrode pad 12 formed on a SiO film and a ring-shaped metal electrode 13 formed along an edge of the light receiving area 11 so as to minimize a capacitance that became a problem when a light receiving area is increased to have a large caliber. In this connection, a parasitic capacitance may be minimized by transferring a current, generated in correspondence to an input optical signal, to an external circuit through the ring-shaped electrode 13 Ohmic-contacted with the light receiving area 11 and the electrode pad 12 connected to the ring-shaped electrode 13.
[18] However, in case of using the ring-shaped electrode 13, a process time for alignment is increased due to back reflectance by the metal ring during assembling OSA (Optical Sub Assembly). In addition, in case a large light receiving area 11 over a certain diameter is provided, a carrier transport time is elongated, so a frequency response speed is decreased. Disclosure of Invention
Technical Problem
[19] The present invention is designed in consideration of the above problems, and therefore it is an object of the invention to provide a photodiode having an electrode structure that may solve reflection problem occurring when being aligned to an optical fiber, minimize a capacitance and also reduce a transport time of a carrier. Technical Solution
[20] In order to accomplish the above object, the present invention provides a photodiode, which includes a light receiving area having a junction structure of a compound semiconductor for photoelectric conversion; a first electrode having a net structure Ohmic-contacted to a light input region on one side of the light receiving area; and a second electrode formed on the other side of the light receiving area in cor¬ respondence to the first electrode.
[21] Preferably, the net structure of the first electrode has a square pattern whose length and width are 30 to 50μm.
[22] In addition, it is preferred that the first electrode is composed of wire whose width is 1 to 4μm.
[23] The photodiode of the present invention may further include a ring-shaped electrode electrically connected to the first electrode and Ohmic-contacted along an edge of the light input region of the light receiving area.
[24] The light receiving area may include a N-type InP substrate; a N-type InP buffer layer formed on the substrate; an InGaAs absorption layer formed on the buffer layer; and an InP layer formed on the absorption layer.
[25] Preferably, the photodiode of the present invention further includes a SiO insulation film formed on the InP layer around the light input region; a non-reflective film passivated on the SiO insulation film; and an electrode pad formed on the non- reflective film and connected to the first electrode.
[26] The InGaAs absorption layer preferably has a thickness of 2.0 to 3.4μm.
Brief Description of the Drawings
[27] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:
[28] FIG. 1 is a plane view showing configuration of a conventional photodiode;
[29] FIG. 2 is a plane view showing another configuration of a conventional photodiode;
[30] FIG. 3 is a plane view showing configuration of a photodiode according to a preferred embodiment of the present invention;
[31] FIG. 4 is a partially sectioned perspective view showing inner configuration of the photodiode according to the preferred embodiment of the present invention;
[32] FIG. 5 is a graph showing a frequency response characteristic of the photodiode according to one embodiment of the present invention;
[33] FIG. 6 shows a system configuration for measuring an impulse response of a photodiode;
[34] FIGs. 7 and 8 are plane views showing alignment positions when measuring an impulse response of a photodiode, according to comparative examples;
[35] FIGs. 9 and 10 are graphs showing impulse characteristics corresponding to optical alignment of the photodiode according to comparative examples; and
[36] FIGs. 11 and 12 are graphs showing frequency response features of the photodiode according to comparative examples. Best Mode for Carrying Out the Invention
[37] The present invention will be described in detail referring to the drawings, the terms used should not be construed as limited to general and dictionary meanings but based on the meanings and concepts of the invention on the basis of the principle that the inventor is allowed to define terms appropriate for the best explanation. Therefore, the descriptionherein the scope of the inventiont be understood that other and modi¬ fications could be made thereto without departing from the spirit and scope of the invention.
[38] FIG. 3 is a plane view showing configuration of a photodiode according to a preferred embodiment of the present invention, and FIG. 4 is a partially sectioned perspective view thereof.
[39] Referring to FIGs. 3 and 4, the photodiode according to the preferred embodiment of the present invention includes a light receiving area 100 having a multi-layer junction structure of a compound semiconductor for photoelectric conversion, a first electrode 101 provided in a light input region of the light receiving area 100 and having a net structure, and a second electrode 107 formed on the other side of the light receiving area 100.
[40] The first electrode 101 having a net structure is provided in the light input region of the light receiving area 100. The net structure of the first electrode 101 is Ohmic- contacted to an upper portion of the light receiving area 100, and it is configured so that square wire patterns of 30 to 50μm equal to or larger than a diameter of a general optical communication light are repeated. Here, the net-type wire pattern of the first electrode 101 preferably has a width of 1 to 4μm so as not to affect on back reflectance of the photodiode and also not to give an effect on laser welding in the assembling procedure. More preferably, the wire of the first electrode 101 has a width of 2 to 4μm. The first electrode 101 is preferably composed to have multi layers of Ti/Pt/Au or Cr/ Au.
[41] Preferably, a ring-shaped electrode 102 may be further provided to an edge of the light input region of the light receiving area 100. The ring-shaped electrode 102 Ohmic-contacted with the light receiving area 100 surrounds the edge of the net structure and also is electrically connected to the first electrode 101.
[42] An electrode pad 103 electrically connected to the first electrode 101 and the ring- shaped electrode 102 to transport a carrier to an external circuit is provided around the light input region of the light receiving area 100. Here, around the light input region of the light receiving area 100, a SiO insulation film 105 having a thickness of about lμm and a non-reflective film 106 made of Si N of about 1000 to 2000A passivated on the SiO insulation film 105 are provided. The electrode pad 103 is formed on the non-reflective film 106 so as to minimize a parasitic capacity, and it is also preferably composed of multi layers of Ti/Pt/Au or Cr/ Au.
[43] The light receiving area 100 has a compound semiconductor layer for generation of a carrier corresponding to an input light and a PN-junction structure for giving an electric field to transport the carrier to an electrode. Preferably, the light receiving area 100 may include a N-type InP substrate 108, a N-type InP buffer layer 109 formed on the substrate 108, an InGaAs absorption layer 110 formed on the buffer layer 109, and an InP layer 111 formed on the absorption layer 110. The InP layer 111 is provided with a P-type InP region 104 formed by Zn diffusion, and the second electrode 107 corresponding to the first electrode 101 having a net structure is formed on the lower surface of the substrate 108. Here, the light receiving area 100 is not limited to the above configuration but may have various modifications such as a known PIN junction structure.
[44] A frequency response giving greatest effects on the performance of the photodiode is limited by transmit time and capacitance for the absorption layer 110. That is to say, if thickness of the absorption layer 110 is increased too great, much transit time is consumed, while, if the thickness is decreased, capacitance is increased, thereby dete¬ riorating the frequency response characteristic. In consideration of the above, the InGaAs absorption layer 110 preferably has a thickness of 2.0 to 3.4μm, and the light receiving area 100 preferably has a diameter of about 100 to 300μm. In particular, in case a photodiode is used for the receiving purpose for optical communication, the light receiving area 100 preferably has a diameter of 100 to 150μm.
[45] The InP buffer layer 109, the InGaAs absorption layer 110, the InP layer 111 or the like of the light receiving area 100 may be formed subsequently by means of a film growth technique used in a common semiconductor manufacturing procedure. In addition, the Zn diffusion region 104 in the upper portion of the InP layer 111 may be formed by means of a masking technique using common PECVD (Plasma Enhanced Chemical- Vapor Deposition), a photolithography technique, a lift-off technique, RTA (Rapid Thermal Annealing) or the like, and electrode structure such as the first electrode 101 having a net pattern, the ring-shaped electrode 102, the electrode pad 103 and the second electrode 107 may be prepared using a common E-beam deposition technique, a lift-off technique or wet etching.
[46] Hereinafter, a process for fabricating a photodiode according to the present invention will be described, focused on forming of the Zn diffusion region 104, the electrodes or the like of the light receiving area 100.
[47] First, for an epitaxial wafer in which the substrate 108, the InP buffer layer 109, the
InGaAs absorption layer 110, the InP layer 111 and an InGaAs capping layer (not shown) as a protective film are formed by means of growth using MOCVD, the InGaAs capping layer having a thickness of 0.1 μm is removed using a sulphuric acid etching solution, and a Si N film is deposited using a PECVD device to make a mask
3 4 for ZN diffusion. [48] After the deposition process is completed, a PR (Photo Resist) pattern for Zn diffusion is made on the Si N film by means of photolithography, and then Si N exposed by the PR pattern is etched using BOE (Buffered Oxide Etchant) solution. [49] After completing the BOE etching, the wafer is put into a thermal evaporator chamber together with Zn P , and then Zn P is deposited on the wafer in a vacuum of
3 2 3 2
2 10 Torr. After the deposition, the lift-off process is executed for the wafer so that Zn P and PN are all removed with leaving a part of Zn P for Zn diffusion. Here, the lift-off process is executed in a way that the PR is melt using acetone solution or the like so that the PR and Zn P deposited on the PR are separated from the substrate.
[50] Since SiO is deposited on the upper surface of the wafer by use of PECVD, out- diffusion of the wafer is prevented when Zn is diffused at high temperature.
[51] Then, the wafer on which SiO is capped is put into a RTA chamber under nitrogen environments and then Zn-RTA diffusion is executed for 4 minutes at 55O0C. After the diffusion process is completed, the SiO capping layer is removed by means of BOE, and then Zn P in a light receiving area remained after diffusion is removed using a nitrogen etching solution.
[52] Subsequently, in order to minimize a parasitic capacitance caused by the electrode pad, a PECVD device is used to deposit a SiO insulation layer in a thickness of lμm on the upper surface of the wafer, and then SiO in a region where Zn is diffused is removed using photolithography and BOE solution.
[53] After that, the non-reflective film (Si N ) 106 is formed by means of PECVD, and then a P-metal electrode, which is the first electrode having a net pattern, is formed using the photolithography and lift-off processes. Here, the P-metal electrode is formed in a way that, as for the wafer on which a PR pattern is formed through pho¬ tolithography, Ti/Pt/Au is deposited in a high vacuum of 1 10 Torr in a thickness of 400/600/1200 by using an E-beam evaporator, and then the metal film on an un¬ necessary area is removed by means of the lift-off process, followed by executing Ohmic contact annealing in the RTA chamber. After the P-metal electrode having a net structure is formed as mentioned above, an electrode pad is formed at one side on the SiO insulation layer adjacent to the P-metal electrode. [54] Subsequently, a lapping process is executed for the back surface of the wafer to make a thickness of lOOμm, then Ti/Pt/Au adopted as a N-metal is deposited in a thickness of 400/600/3000A and then Ohmic contact annealing is again executed in
RTA. Then, N-metal, which is the second electrode corresponding to the P-metal having a net structure, is formed. [55] After the above unit processes are all completed, the wafer is cut into a certain size as shown in FIG. 4, and then a photodiode having a net structure in the light receiving area is obtained.
Mode for the Invention [56] Hereinafter, the photodiode according to the above embodiment and photodiodes according to the prior art (comparative examples) are comparatively explained for better understanding of the present invention. [57]
[58] Embodiment
[59] A photodiode in which a light receiving area has a diameter of 150μm and an
InGaAs absorption layer has a thickness of 2.0μm and which includes an electrode having a net structure and an electrode pad was fabricated. [60] After measuring a frequency response speed of the photodiode of this embodiment, it was found that a frequency corresponding to 3dB bandwidth was 0.58 GHz when V R
=5 V as an example, as shown in FIG. 5.
[61]
[62] Comparative Example 1
[63] A photodiode in which a light receiving area has a diameter of 120μm and an
InGaAs absorption layer has a thickness of 3.4μm and which includes only an electrode pad directly formed on the InP substrate was fabricated (see FIG. 1).
[64]
[65] Comparative Example 2
[66] A photodiode in which a light receiving area has a diameter of 120μm and an
InGaAs absorption layer has a thickness of 3.4μm and which includes a ring-shaped electrode and an electrode pad formed on the SiO film was fabricated (see FIG. 2).
[67]
[68] Change of response speed of the photodiodes according to the change of position of light receiving alignment was examined through impulse response for the comparative examples 1 and 2. As shown in FIG. 6, an optical axis was adjusted in an optical stage 200 of a common impulse response measuring system so that responsivity of the photodiodes became maximized, and then a step response of the photodiodes was measured using LSA 3707 A 201. Measuring conditions were set so that Test power = - 2.5 dBm, V = 5.0V, R = 50, 1 = 1550nm, Electrical delay = 6ns, Time span = 5ns,
R L and then impulse responses were measured and compared with changing the position of light in correspondence to each point A, B, C, of the light receiving unit 11 as shown in FIGs. 7 and 8.
[69] As a result of the measurement, as shown in FIGs. 9 and 10, it was found that the photodiode of the comparative example 2 showed less change of response speed acco rding to the change of position of beam than the photodiode of the comparative example 1. Thus, it may be understood that, in case the light receiving area is configured to have a large caliber according to the present invention, it is preferable that the change of response speed according to the change of position of light receiving alignment is minimized by adding a ring-shaped electrode.
[70]
[71] Comparative Example 3
[72] A photodiode in which a light receiving area has a diameter of 150μm and an
InGaAs absorption layer has a thickness of 2.0μm and which includes only an electrode pad directly formed on the InP substrate was fabricated (see FIG. 1).
[73]
[74] Comparative Example 4
[75] A photodiode in which a light receiving area has a diameter of 150μm and an
InGaAs absorption layer has a thickness of 2.0μm and which includes a ring-shaped electrode and an electrode pad formed on the SiO film was fabricated (see FIG. 2).
[76]
[77] As a result of measuring a frequency response speed for the photodiodes of the comparative examples 3 and 4, it was found that, when V R = 5.0V, a frequency cor- responding to 3dB bandwidth was 0.33 GBz in the comparative example 3, and a frequency corresponding to 3dB bandwidth was 0.5 GBz in the comparative example 4, as shown in FIGs. 11 and 12 respectively.
[78] According to the above measurement results, it may be understood that the photodiode provided with an electrode having a net structure in the light receiving area shows an improved carrier transport characteristic, thereby capable of improving a frequency response characteristic corresponding to 3dB bandwidth rather than the con¬ ventional photodiode having only the ring-shaped electrode.
[79] The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Industrial Applicability
[80] The photodiode configured as above according to the present invention gives the following effects.
[81] First, since the back reflection characteristic is improved at assembling of the OSA
(Optical Sub Assembly), it is possible to reduce a process time for optical fiber alignment, increase an allowable limit for alignment accuracy during the laser welding process owing to the large light receiving area, and also enable manual alignment in a pressuring manner.
[82] Second, since the electrode structure is kept stably due to the feature of the net structure though a width of the electrode wire is narrowed, it is possible to improve reflection characteristics and reduce a carrier transport time to an external circuit.
[83] Third, it is possible to improve a frequency response characteristic regarding a diameter of the same light receiving area in comparison to a photodiode using only a ring-shaped electrode.
[84] Fourth, since a light receiving area having a large caliber of, for example, 100 to
300μm is configured, the photodiode of the present invention may be useful as a photodiode for monitors and for receiving an optical signal of 155 Mbps to 2.5 Gbps.

Claims

Claims
[1] A photodiode, comprising: a light receiving area having a junction structure of a compound semiconductor for photoelectric conversion; a first electrode having a net structure Ohmic-contacted to a light input region on one side of the light receiving area; and a second electrode formed on the other side of the light receiving area in corre¬ spondence to the first electrode.
[2] The photodiode according to claim 1, wherein the net structure of the first electrode has a square pattern whose length and width are 30 to 50μm.
[3] The photodiode according to claim 1, wherein the first electrode is composed of wire whose width is 1 to 4 μm.
[4] The photodiode according to any of claims 1 to 3, further comprising a ring- shaped electrode electrically connected to the first electrode and Ohmic- contacted along an edge of the light input region of the light receiving area.
[5] The photodiode according to claim 1, wherein the light receiving area includes: a N-type InP substrate; a N-type InP buffer layer formed on the substrate; an InGaAs absorption layer formed on the buffer layer; and an InP layer formed on the absorption layer.
[6] The photodiode according to claim 5, further comprising: a SiO insulation film formed on the InP layer around the light input region; a non-reflective film passivated on the SiO insulation film; and an electrode pad formed on the non-reflective film and connected to the first electrode.
[7] The photodiode according to claim 5, wherein the InGaAs absorption layer has a thickness of 2.0 to 3.4μm.
PCT/KR2005/002084 2004-09-24 2005-06-30 Photodiode having electrode structure for large optical signal receiving area WO2006033516A1 (en)

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JPH01196182A (en) * 1988-01-31 1989-08-07 Shimadzu Corp Photodiode
JPH0494579A (en) * 1990-08-10 1992-03-26 Mitsubishi Electric Corp Semiconductor photodetector
JPH1168144A (en) * 1997-08-26 1999-03-09 Matsushita Electric Ind Co Ltd Light-receiving element and manufacture thereof
JP2001024210A (en) * 1999-07-06 2001-01-26 Matsushita Electric Ind Co Ltd Photo-detecting element and its manufacture

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