A heterojunction photodetector and a preparation method thereof

Abstract

This invention provides a heterojunction photodetector and its fabrication method. The photodetector comprises, from bottom to top, a substrate layer, a contact layer, a collector, a base, and an oxide emitter. n-type contact electrodes are respectively disposed on the oxide emitter and the contact layer. The contact layer and the collector are made of n-type conductive nitride materials. The base is made of p-type conductive nitride material. This invention utilizes a non-epitaxy process to fabricate an oxide heterostructure on a nitride material, thus combining the advantages of oxide materials being easily processed by wet methods and nitride materials having high photoelectric efficiency. It avoids damage to the emitter caused by dry etching, thereby reducing defects and leakage introduced during the process and achieving higher device performance. It can cover the deep ultraviolet to near-infrared bands corresponding to the bandgap of III-V group nitride and oxide materials, and has the potential for dual-color detection and customized wavelength detection.

Description

Technical Field

[0001] This invention relates to the field of photodetector technology, and in particular to a heterojunction photodetector and its fabrication method. Background Technology

[0002] Photoelectric detection has a wide range of applications in the ultraviolet, visible, and infrared bands. For example, ultraviolet photodetectors can be used for flame detection, biological environment monitoring, and space optical communication; visible light detection can be used for visible light communication, optical imaging, and various experimental testing and research; and near-infrared photodetectors are an indispensable part of current optical communication systems. For these photoelectric detection fields, detectors need to have high stability, high responsivity, fast response speed, and excellent wavelength selectivity, enabling sensitive detection of weak signals, even single-photon signals, with low operating bias and without external signal amplifiers.

[0003] For commonly used silicon-based semiconductor devices, quantum efficiency is severely limited by the indirect bandgap and narrow bandgap of silicon materials, and complex filtering systems are required to meet wavelength selectivity requirements. However, with advancements in semiconductor material growth technology, detectors made from gallium nitride (GaN) with a direct bandgap and various ternary compounds with continuously tunable bandgap, as well as wide-bandgap oxides such as gallium oxide (Ga2O3) and zinc oxide (ZnO), have become a hot topic in the research and development of ultraviolet, visible, and near-infrared photodetectors.

[0004] However, there are still many shortcomings in the structure and fabrication process of photodetectors in nitride-based single-material systems. Currently, the most common photodetector structures that can achieve high internal gain are avalanche photodiodes (APDs) and heterojunction phototransistors (HPTs). The former mainly utilizes a high external electric field to accelerate and ionize charge carriers to generate an avalanche effect, thus requiring very high-quality crystal materials; while the latter, with its quasi-vertical structure, suffers from material damage caused by ICP dry etching during fabrication, which severely affects recombination and leakage current, limiting the detector's quantum efficiency and weak light response level. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a heterojunction photodetector and its fabrication method. This invention can achieve the technical effects of high gain, low dark current, and wide-range detection.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a heterojunction photodetector, comprising a substrate layer, a contact layer, a collector electrode, a base electrode, and an oxide emitter arranged sequentially from bottom to top;

[0008] The oxide emitter and the contact layer are respectively provided with n-type contact electrodes;

[0009] The contact layer and the collector are made of n-type conductive nitride material; the base is made of p-type conductive nitride material.

[0010] Preferably, the substrate layer is any one of sapphire, silicon, gallium nitride, gallium oxide, and zinc oxide.

[0011] Preferably, the material of the n-type contact electrode is a stack of Ti and Al, or a stack of Ni and Au, or a stack of Ti and Au.

[0012] Preferably, the nitride material is GaN, AlGaN, or InGaN.

[0013] Preferably, the electron concentration of the contact layer and the base is not less than 1×10⁻⁶. 16 cm -3 The electron concentration of the collector electrode is not less than 1×10⁻⁶. 15 cm -3 .

[0014] Preferably, the contact layer is doped using unintentional doping or Si doping.

[0015] The collector is doped using n-type doping, polarization doping, or unintentional doping.

[0016] The base is doped using either Mg doping or polarization doping.

[0017] Preferably, the oxide emitter has an n-type conductive structure, and the material of the oxide emitter includes any one of Ga2O3, ZnO, and SnO2.

[0018] Secondly, the present invention provides a method for fabricating a heterojunction photodetector, comprising the following steps:

[0019] S1) Select the appropriate substrate layer according to the contact layer, and generate the contact layer on the substrate layer using metal-organic chemical vapor deposition or molecular beam epitaxy.

[0020] S2) Fabricate current collectors on the contact layer using metal-organic chemical vapor deposition or molecular beam epitaxy;

[0021] S3) The base electrode is prepared on the collector electrode using metal-organic chemical vapor deposition or molecular beam epitaxy;

[0022] S4) Prepare an oxide emitter on the base using a non-epitaxy method;

[0023] S5) An n-type contact electrode is fabricated on the contact layer and the oxide emitter.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. This invention utilizes a non-epitaxy process to achieve low-cost, high-quality fabrication of oxide heterostructures on nitride materials. This combines the advantages of oxide materials being easy to process with wet methods and nitride materials having high photoelectric efficiency, avoiding damage to the emitter caused by dry etching, thereby reducing defects and leakage introduced by the process and achieving higher device performance.

[0026] 2. This invention achieves flexible adjustment of the detection wavelength range through the high-efficiency and high-quality combination of nitride and oxide. By using specific oxide materials to adjust the target wavelength range and span, it has the potential to realize dual-color detection and customized wavelength detection.

[0027] 3. This invention utilizes oxide materials with wider bandgap as emitters to form a larger heterojunction injection ratio, thereby generating photoelectric amplification and high sensitivity far exceeding those of single-material systems, providing a superior detection option for weak light scenarios in practical ultraviolet detection. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the photodetector in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the photodetector in Embodiment 2 of the present invention;

[0030] In the figure, 101-substrate layer; 102-contact layer; 103-collector; 104-base; 105-oxide emitter; 106-n-type contact electrode. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0032] Example 1

[0033] like Figure 1 As shown, this embodiment provides a heterojunction photodetector, including a substrate layer 101, a contact layer 102, a collector electrode 103, a base electrode 104, and an oxide emitter 105 arranged sequentially from bottom to top; n-type contact electrodes 106 are disposed on the contact layer 102 and the oxide emitter 105.

[0034] In this embodiment, the substrate layer 101 is a Si substrate layer.

[0035] In this embodiment, the contact layer 102, the current collector 103, and the base 104 are all prepared using metal-organic chemical vapor deposition; wherein, the contact layer 102 is made of Si-doped GaN material with an electron concentration of 2 × 10⁻⁶. 18 cm -3 The collector 103 is Si-doped with an electron concentration of 2×10⁻⁶. 16 cm -3 The base electrode is Mg-doped with a hole concentration of 6×10⁻⁶. 17 cm -3 .

[0036] In this embodiment, the thicknesses of the contact layer 102, the collector 103, and the base 104 are 4 μm, 120 nm, and 100 nm, respectively.

[0037] In this embodiment, the oxide emitter 105 is made of Ga2O3 and is prepared by atomic layer deposition at a temperature of 150°C. The oxide emitter 105 achieves n-type conductivity through F ion implantation, with an electron concentration of 1×10⁻⁶. 18 cm -3 The oxide emitter 105 has a thickness of 80 nm.

[0038] In this embodiment, the Ga2O3 bandgap of the oxide emitter 105 is significantly higher than that of GaN, thus enabling a high electron injection ratio and achieving high photoelectric gain and high-sensitivity detection.

[0039] In this embodiment, the n-type contact electrode 106 is a Ti and Au metal stack with thicknesses of 20 nm and 80 nm, respectively; the preparation method is thermal evaporation coating; the preparation process includes annealing in a nitrogen atmosphere after coating, with an annealing temperature of 810°C and an annealing time of 1 minute. In this embodiment, the n-type contact electrode 106 on the oxide emitter 105 serves as the cathode, and the n-type contact electrode 106 on the contact layer 102 serves as the anode.

[0040] Example 2

[0041] like Figure 2 As shown, this embodiment provides a heterojunction photodetector, including a substrate layer 101, a contact layer 102, a collector electrode 103, a base electrode 104, and an oxide emitter 105 arranged sequentially from bottom to top; n-type contact electrodes 106 are disposed on the contact layer 102 and the oxide emitter 105.

[0042] In this embodiment, the substrate 101 is a sapphire α-Al2O3 substrate 101.

[0043] In this embodiment, the contact layer 102, collector 103, and base 104 are all fabricated using molecular beam epitaxy. The contact layer 102 is made of unintentionally doped GaN material, and its electron concentration is 4 × 10⁻⁶. 16 cm -3 The collector 103 is made of polarization-induced doped n-type AlGaN material with a thickness of 100 nm. During growth, the composition is linearly and gradually changed from 0% to 10%, resulting in an electron concentration of 5 × 10⁻⁶. 17 cm -3 ;

[0044] The base electrode is made of polarization-induced doped p-type AlGaN material with a thickness of 100 nm. During growth, the composition is linearly and gradually changed from 10% to 0%, resulting in a hole concentration of approximately 4 × 10⁻⁶. 17 cm -3 .

[0045] In this embodiment, the oxide emitter 105 is made of ZnO, prepared by atomic layer deposition at a temperature of 130°C, and unintentionally doped with n-type electrons by oxygen annealing at 700°C, resulting in an electron concentration of 1×10⁻⁶. 19 cm -3 The thickness is 40nm.

[0046] In this embodiment, the ZnO bandgap of the oxide emitter 105 is close to that of AlGaN, which can achieve effective transistor electron injection. At the same time, due to the high electron concentration of ZnO, extremely high phototransistor gain can be achieved, enabling high-sensitivity and high-speed ultraviolet detection.

[0047] In this embodiment, the n-type contact electrode 106 is made of a Ti-Al or Ni-Au multilayer metal material with thicknesses of 20, 60, 20, and 80 nm, respectively. In this embodiment, the n-type contact electrode 106 on the oxide emitter 105 serves as the cathode, and the n-type contact electrode 106 on the contact layer 102 serves as the anode. There are two cathodes and two anodes in this embodiment.

[0048] Example 3

[0049] The heterojunction photodetector provided in this embodiment is based on Embodiment 1, except that the materials of the contact layer 102, collector 103, and base 104 are replaced with In. 0.15 GaN; The wavelength detection range of the heterojunction photodetector in this embodiment is visible light and ultraviolet light with wavelengths below 450 nm.

[0050] Example 4

[0051] The heterojunction photodetector provided in this embodiment is based on Example 1, except that the oxide emitter material is replaced with SnO2, and the preparation method is magnetron sputtering.

[0052] Example 5

[0053] The heterojunction photodetector provided in this embodiment is based on that in Embodiment 2, and the oxide emitter ZnO is prepared by metal thermal oxidation, with an electron concentration of 2 × 10⁻⁶. 19 cm -3 .

[0054] Example 6

[0055] The heterojunction photodetector provided in this embodiment differs from that in Embodiment 3 in that the oxide emitter material used is α-Fe2O3, the preparation method is atomic layer deposition, and the detection wavelength range of the device is visible light and ultraviolet light below 600nm.

[0056] Example 7

[0057] This embodiment provides a method for fabricating a heterojunction photodetector, including the following steps:

[0058] S1) Select a suitable substrate layer. The substrate material can be selected according to the type of material of the contact layer to be grown: when the contact layer material is AlGaN, sapphire, aluminum nitride, and gallium oxide are preferred substrates; when the epitaxial layer material of the contact layer is GaN or InGaN, silicon, sapphire, zinc oxide, and self-supporting gallium nitride substrates are preferred substrates.

[0059] S2) The nitride contact layer, nitride current collector and nitride base are fabricated by epitaxial methods such as metal-organic chemical vapor deposition or molecular beam epitaxy.

[0060] The nitride contact layer material can be an n-type conductive AlGaN, GaN, or InGaN.

[0061] Preferably, an appropriate amount of silane gas can be introduced during the growth process to achieve n-type doping of the contact layer, or polarized n-type doping can be achieved by gradually changing the material composition.

[0062] Preferably, when polarized n-type doping is used, the material composition in the nitride contact layer changes by gradually decreasing the lattice along the

[0001] crystal direction, for example, gradually increasing the Al content in AlGaN grown along the

[0001] crystal direction.

[0063] The nitride current collector material can be an n-type conductive AlGaN, GaN, or InGaN.

[0064] Preferably, the lateral lattice size of the collector material should not be smaller than that of the contact layer material. For example, AlGaN with the same Al composition as the contact layer material or AlGaN with a lower Al composition can be used. Similarly, n-type doping of the collector can be achieved by introducing an appropriate amount of silane gas during the growth process, or polarized n-type doping can be achieved by gradually changing the material composition.

[0065] The nitride base material can be p-type conductive AlGaN, GaN, or InGaN.

[0066] Preferably, the lateral lattice size of the base material should not be smaller than that of the collector material. For example, AlGaN with the same Al composition as the contact layer material or AlGaN with a lower Al composition can be used. P-type doping of the base can be achieved by introducing an appropriate amount of magnesium pyrocene gas during the growth process, or by gradually changing the material composition.

[0067] Preferably, when polarized p-type doping is used, the material composition in the nitride base changes by gradually increasing the lattice size along the

[0001] crystal direction, for example, gradually decreasing the Al content in AlGaN grown along the

[0001] crystal direction.

[0068] S3) Prepare oxide emitters using non-epitaxy methods. The oxide emitter material includes, but is not limited to, any one of Ga2O3, ZnO, and SnO2, and its conductivity type is n-type conductivity. The preparation methods include, but are not limited to, atomic layer deposition, magnetron sputtering, and thermal oxidation.

[0069] Preferably, the band gap of the oxide emitter material should not be less than the band gap of the nitride base material. For example, when the nitride base material is GaN, the oxide emitter can be Ga2O3 or SnO2; when the nitride base material is InGaN, the oxide emitter can be ZnO. The n-type conductivity of the oxide emitter can be achieved during the fabrication process through impurity doping, intrinsic defect doping, or by ion implantation after growth. For example, after fabricating the Ga2O3 emitter, n-type conductivity can be achieved by F ion implantation; or when fabricating the ZnO emitter, n-type doping can be achieved by reducing the O source partial voltage to increase O vacancies.

[0070] S4) The emitter step pattern is formed by wet etching, and the base and collector are further etched by dry etching to fabricate the n-type contact electrode.

[0071] The fabrication of the device requires first using standard photolithography to etch and expose the oxide material outside the emitter, then using wet solvent etching to form the emitter step, and then using dry etching to remove the base and collector portions below, exposing the contact layer material; subsequently, using photolithography to fabricate n-type contact electrodes on the oxide emitter and contact layer to form the device.

[0072] The emitter steps can be fabricated using an etchant corresponding to the emitter material, such as HCl solution etching the ZnO emitter to form the emitter steps.

[0073] The etching of the base and collector can be achieved through plasma etching or similar methods, thereby exposing the underlying contact layer material.

[0074] The n-type contact electrode can be fabricated using methods such as thermal evaporation or magnetron sputtering. The cathode metal on the oxide emitter and the anode metal on the contact layer can be, but are not limited to, the same material. Preferably, they can be a stacked material of Ti and Al or Ni and Au, and ohmic contacts are formed by nitrogen annealing after fabrication.

[0075] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of the present invention. Various changes and modifications may be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A heterojunction photodetector, characterized in that, It includes a substrate layer (101), a contact layer (102), a collector (103), a base (104), and an oxide emitter (105) arranged sequentially from bottom to top. The oxide emitter (105) and the contact layer (102) are respectively provided with n-type contact electrodes (106); the n-type contact electrode (106) on the oxide emitter (105) serves as the cathode, and the n-type contact electrode (106) on the contact layer (102) serves as the anode; The contact layer (102) and the collector (103) are made of n-type conductive nitride material; the base (104) is made of p-type conductive nitride material.

2. A heterojunction photodetector according to claim 1, characterized in that: The substrate layer (101) is made of any one of sapphire, silicon, gallium nitride, gallium oxide, and zinc oxide.

3. A heterojunction photodetector according to claim 1, characterized in that: The material of the n-type contact electrode (106) is a Ti-Al stack, a Ni-Au stack, or a Ti-Au stack.

4. A heterojunction photodetector according to claim 1, characterized in that: The nitride material is GaN, AlGaN, or InGaN.

5. A heterojunction photodetector according to claim 1, characterized in that: The electron concentration of the contact layer (102) and the base (104) is not less than 1×10⁻⁶. 16 cm -3 The electron concentration of the collector (103) is not less than 1×10⁻⁶. 15 cm -3 .

6. A heterojunction photodetector according to claim 1, characterized in that: The contact layer (102) is doped using unintentional doping or Si doping. The doping method of the collector (103) is n-type doping, polarization doping, or unintentional doping; The base (104) is doped using Mg doping or polarization doping.

7. A heterojunction photodetector according to claim 1, characterized in that: The oxide emitter (105) has an n-type conductive structure, and the material of the oxide emitter (105) includes any one of Ga2O3, ZnO, and SnO2.

8. A method for fabricating a heterojunction photodetector, characterized in that, Includes the following steps: S1) Select the corresponding substrate layer (101) according to the contact layer (102), and generate the contact layer (102) on the substrate layer (101) using metal-organic chemical vapor deposition or molecular beam epitaxy. S2) The collector electrode (103) is prepared on the contact layer (102) by metal-organic chemical vapor deposition or molecular beam epitaxy. S3) The base electrode (104) is prepared on the collector electrode (103) by metal-organic chemical vapor deposition or molecular beam epitaxy. S4) An oxide emitter (105) is prepared on the base (104) by a non-epitaxy method. S5) An n-type contact electrode (106) is prepared on the contact layer (102) and the oxide emitter (105).

9. The method for fabricating a heterojunction photodetector according to claim 8, characterized in that: The contact layer (102) and collector (103) are n-type conductive nitride materials; the base (104) is a p-type conductive nitride material; the nitride material is GaN, AlGaN, or InGaN.

10. The method for fabricating a heterojunction photodetector according to claim 8, characterized in that: Wet etching is used to form an emitter step, and then dry etching is used to remove the base (104) and collector (103) below the emitter step, exposing the contact layer (102); an n-type contact electrode (106) is fabricated on the oxide emitter (105) and contact layer (102) by photolithography to form a photodetector device. The etchant used to fabricate the emitter steps is selected in accordance with the etchant material. The etching of the base (104) and collector (103) is achieved by plasma etching; The n-type contact electrode (106) is prepared by thermal evaporation or magnetron sputtering. The n-type contact electrode (106) on the oxide emitter (105) serves as the cathode, and the n-type contact electrode (106) on the contact layer (102) serves as the anode.

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