阅读说明：本技术 一种双极型可见光探测器及其制备方法 (Bipolar visible light detector and preparation method thereof ) 是由 江灏 张苏朋 吕泽升 于 2020-03-09 设计创作，主要内容包括：本发明涉及一种双极型可见光探测器及其制备方法,双极型可见光探测器包括衬底、外延层、沉积的金属电极,外延层按照自下而上的生长顺序依次为成核层、过渡层、Si掺杂n型GaN下欧姆接触层、Si掺杂n型Al<Sub>x</Sub>Ga<Sub>1-x</Sub>N组分渐变层、非故意掺杂Al<Sub>y</Sub>Ga<Sub>1-y</Sub>N层、非故意掺杂Al<Sub>z</Sub>Ga<Sub>1-z</Sub>N组分渐变层、具有周期GaN薄插入层的非故意掺杂In<Sub>j</Sub>Ga<Sub>1-j</Sub>N光吸收层、Si掺杂n型In<Sub>k</Sub>Ga<Sub>1-k</Sub>N组分渐变层、Si掺杂n型GaN上欧姆接触层,金属电极包括下欧姆接触电极和上欧姆接触电极。本发明具有光电增益高、响应速度快和工作电压低的优点。(The invention relates to a bipolar visible light detector and a preparation method thereof, the bipolar visible light detector comprises a substrate, an epitaxial layer and a deposited metal electrode, wherein the epitaxial layer sequentially comprises a nucleating layer, a transition layer, a Si-doped n-type GaN lower ohmic contact layer and a Si-doped n-type Al according to the growth sequence from bottom to top x Ga 1‑x Graded layer of N component, unintentionally doped with Al y Ga 1‑y N layer, unintentionally doped with Al z Ga 1‑z N-composition graded layer, unintentionally doped In with periodic GaN thin insertion layer j Ga 1‑j N light absorption layer, Si-doped N-type In k Ga 1‑k A graded N-component layer, an ohmic contact layer on Si-doped N-type GaN, and a metal electrode including a lower portionAn ohmic contact electrode and an upper ohmic contact electrode. The invention has the advantages of high photoelectric gain, high response speed and low working voltage.)

1. The bipolar visible light detector is characterized by comprising a substrate (101), an epitaxial layer grown on the substrate and a deposited metal electrode, wherein the epitaxial layer grows from bottom to topThe nucleation layer (102), the transition layer (103), the Si-doped n-type GaN lower ohmic contact layer (104) and the Si-doped n-type Al are sequentially arranged in sequence_xGa_1-xA graded layer (105) of N-component, unintentionally doped with Al_yGa_1-yN layer (106), unintentionally doped Al_zGa_1-zN-composition graded layer (107), unintentionally doped In with periodic GaN thin insertion layer_jGa_1-jAn N light absorption layer (108), Si-doped N-type In_kGa_1-kThe N-component graded layer (109), the Si-doped N-type GaN upper ohmic contact layer (110), and the metal electrodes respectively comprise a lower ohmic contact electrode (111) deposited on the Si-doped N-type GaN lower ohmic contact layer (104) and an upper ohmic contact electrode (112) deposited on the Si-doped N-type GaN upper ohmic contact layer (110).

2. The bipolar type visible light detector according to claim 1, wherein said substrate (101) is a sapphire, silicon carbide, gallium nitride, aluminum nitride or silicon substrate, said nucleation layer (102) is a low temperature GaN or AlN nucleation layer with a thickness in the range of 10-35nm, said transition layer (103) is a high temperature GaN, AlN or AlGaN transition layer with a thickness in the range of 0.2-3 μm, and said Si doped n type GaN lower ohmic contact layer (104) has an electron concentration of 3 × 10¹⁷-5×10¹⁸cm^-3The thickness is 0.2-2 μm.

3. The bipolar type visible light detector of claim 1, wherein said Si is doped n-type Al_xGa_1-xThe Al component x in the N component gradient layer (105) is linearly and gradually changed, the initial value of x is 0, the end value range is 0.1-0.2, the layer thickness range is 50-200nm, and the electron concentration in the layer is 3 × 10¹⁷-5×10¹⁸cm^-3(ii) a The unintentional doping with Al_yGa_1-yThe Al component y in the N layer (106) has a termination value of x and a thickness of 3-10nm, and the Al is not intentionally doped_zGa_1-zThe Al component z in the N component gradient layer (107) changes linearly, the initial value of z is less than or equal to y, the final value is 0, and the layer thickness is 50-200 nm.

4. The bipolar type visible light detector of claim 1Characterized In that the In is unintentionally doped_jGa_1-jThe band gap width of the N light absorption layer (108) corresponds to a wavelength range of 400-580 nm, the total thickness is 40-100nm, and the In is not intentionally doped_jGa_1-jA GaN thin insertion layer with the thickness of 1-3nm is arranged every 10-20nm in the N light absorption layer (108).

5. The bipolar type visible light detector of claim 1, wherein said Si is doped n-type In_kGa_1-kThe In component k In the N component gradient layer (109) is linearly gradient, the initial value of k is l, the final value is 0, and the electron concentration range In the layer is 3 × 10¹⁷-5×10¹⁸cm^-3The layer thickness is 10-100 nm.

6. The bipolar visible light detector of claim 1 wherein said Si doped n-type GaN ohmic contact layer (110) has an electron concentration in the range of 3 × 10¹⁷-5×10¹⁸cm^-3The layer thickness is 30-200 nm.

7. A method for preparing a bipolar type visible light detector according to any one of claims 1 to 6, comprising the steps of:

s1, surface cleaning: organic and inorganic cleaning is adopted to remove impurities and oxide layers on the surface of the wafer;

s2, step manufacturing: a mask layer is manufactured by adopting a standard photoetching technology, and then the mask layer is etched to the Si-doped n-type GaN lower ohmic contact layer (104) by adopting a dry etching process or a wet etching process to form a step (113);

s3, etching damage repair: repairing damage caused by etching on the surface of the wafer by adopting rapid annealing and wet surface treatment;

s4, electrode manufacturing: manufacturing a mask layer by adopting a photoetching technology to form an annular electrode pattern, depositing a metal electrode, and stripping to obtain two metal ring electrodes on the upper surface and the lower surface of the step (113); and carrying out alloy annealing treatment on the metal electrode to form ohmic contact.

8. The preparation method of the bipolar type visible light detector of claim 7, wherein in step S3, the etching damage is repaired by performing a high temperature rapid annealing treatment in a high purity nitrogen atmosphere and then performing an alkaline solution wet treatment.

9. The method for manufacturing a bipolar type visible light detector as claimed in claim 7, wherein in said step S4, the metal electrode is a combination of metal layers with Ti/Al as the first two layers; the high-temperature rapid alloy annealing treatment is carried out on the metal electrode in a high-purity nitrogen atmosphere or high vacuum.

10. The method of claim 7, wherein the GaN thin insertion layer is grown at a temperature that is not intentionally doped with In_jGa_1-jThe N light absorption layers (108) are the same, the GaN thin insertion layer grows In a mode of a pulse V group N source, and the Si is doped with N-type In_kGa_1-kGrowth temperature of N-component graded layer (109) and unintentional In doping_jGa_1-jThe N light absorption layers (108) are the same, and the growth temperature of the ohmic contact layer (110) layer on the Si-doped N-type GaN is higher than that of the Si-doped N-type In_kGa_1-kThe N component graded layer (109) is 200-300 ℃ higher.

Technical Field

The invention relates to the technical field of semiconductor visible light detectors, in particular to a bipolar visible light detector and a preparation method thereof.

Background

At present, applications in the fields of visible light communication, biophotonic, fluorescence spectroscopy and the like all put higher demands on the performance of visible light detectors. The group III nitride semiconductor InGaN ternary alloy has an application prospect In visible light detection because the direct and adjustable band gap energy covering the whole visible region from 0.7 to 3.4eV can be realized by changing the component of indium (In); meanwhile, since InGaN is a direct bandgap semiconductor and has the characteristics of high light absorption coefficient and high electron saturation drift velocity, InGaN is a highly-efficient and high-speed material for manufacturing visible light detectors.

Although some of these types of detectors exhibit external quantum efficiencies as high as 60% and low dark currents (IEEE Photonics technologies L etters, vol.31, pp1469,2019), some of the developed InGaN photodetectors have essentially no gain characteristics.

In many photoelectric detection of visible light, a high photoelectric gain characteristic is strongly required. For example, in visible light communication applications, as a core device of a signal receiving end, the photoelectric gain of a visible light detector determines the detection sensitivity thereof, and the detection sensitivity of the device is related to the signal transmission distance and the bandwidth of the whole communication system. In the visible light communication system, as the transmission distance increases, the received signal of the optical receiver is attenuated and weakened, and the signal and noise can be seriously distinguished due to the strong background noise of the outside and the inherent circuit noise. Therefore, in order to ensure high-speed and accurate signal reception, the adoption of the photoelectric detector with high sensitivity, high response speed, high responsivity and low noise is a key factor.

Generally, high photoelectric gain can be achieved by fabricating avalanche photodiodes, photoconductive detectors, phototransistor detectors. However, due to the problems of high density of line defects and point defects, phase separation and the like existing in the current InGaN epitaxial layer, a large number of leakage channels (such as screw dislocations) exist in the active layer of the InGaN photodetector, and it is difficult to realize the avalanche effect under a high electric field; meanwhile, donor-type background carriers with high concentration also exist in the unintended doping layer, which is not beneficial to realizing p-type doping, so that an InGaN-based avalanche photodetector and a phototransistor detector are difficult to manufacture. However, the photoconductive detector cannot meet the requirements of most practical applications due to high dark current and low light response speed.

Disclosure of Invention

The invention aims to overcome at least one defect of the prior art and provides a bipolar visible light detector which is used for solving the problem that a photoconductive detector cannot meet most practical application requirements due to high dark current and low photoresponse speed, and an InGaN-based avalanche photodetector and a phototransistor detector are difficult to manufacture.

The technical scheme adopted by the invention is as follows:

a bipolar visible light detector comprises a substrate, an epitaxial layer and a deposited metal electrode, wherein the epitaxial layer grows on the substrate and sequentially comprises a nucleating layer, a transition layer, a Si-doped n-type GaN lower ohmic contact layer and a Si-doped n-type Al according to the growth sequence from bottom to top_xGa_1-xGraded layer of N component, unintentionally doped with Al_yGa_1-yN layer, unintentionally doped with Al_zGa_1-zN-composition graded layer, unintentionally doped In with periodic GaN thin insertion layer_jGa_1-jN light absorption layer, Si-doped N-type In_kGa_1-kThe metal electrodes respectively comprise a lower ohmic contact electrode deposited on the lower ohmic contact layer of the Si-doped N-type GaN and an upper ohmic contact electrode deposited on the upper ohmic contact layer of the Si-doped N-type GaN.

The invention provides a bipolar visible light detector based on a group III nitride semiconductor, which solves the problems that an InGaN-based photodiode has high leakage current under high bias voltage and p-type doping is difficult to realize due to the influence of high background carrier concentration, and forms the bipolar photodetector with high light induction gain by utilizing the characteristics of relatively high and stable crystallization quality of GaN and AlGaN materials in the group III nitride and the polarization effect of the system materials; meanwhile, the InGaN light absorption layer is subjected to crystallization quality improvement through the insertion period of the GaN thin layer, so that the device has high photoelectric gain which is not possessed by the photodiode except the snow avalanche photodetector, and has the advantages of high response speed and low working voltage.

The principle of the bipolar visible light detector is as follows: by utilizing spontaneous and piezoelectric polarization effects in the wurtzite structure III group nitride epitaxial layer, the unintentionally doped Al with gradually-changed components and bearing the compressive stress is enabled to be_zGa_1-zA longitudinal polarization electric field is generated in the N component gradient layer, under the action of the longitudinal polarization electric field, the Fermi level is close to a valence band, holes ionized from acceptor impurities are accumulated in the layer, the potential of the layer is higher than that of the Si-doped N-type GaN ohmic contact layers on the upper layer and the lower layer, and a potential barrier is formed to block the transport of carriers. Therefore, a low leakage current (i.e., a low dark current) can be achieved without light signal incidence. On the other hand, In is doped unintentionally_jGa_1-jThe N-light absorbing layer acts as an absorbing layer to enable visible light detection. To improve unintentional In doping_jGa_1-jCrystalline quality of N-light absorbing layer using periodic GaN thin insertion layer to enhance unintentional In doping_jGa_1-jSuppressing unintentional In doping by compressive stress In N-type light absorbing layer_jGa_1-jPhase separation In the N light absorbing layer (i.e., the In component is not uniformly distributed, resulting In the presence of localized states, resulting In unintended In doping)_jGa_1-jThe concentration of background carriers in the N light absorption layer is high, so that the problems of not steep absorption edge, electric leakage and the like of a detector are caused). Further, In is doped unintentionally_jGa_1-jThe upper layer of the N light absorption layer slowly releases stress through the InGaN component gradient layer, and an N-type GaN ohmic contact layer is grown to be used for manufacturing a metal contact electrode and serve as an incident window layer. The detector works in the state that the upper and lower ohmic contact electrodes are respectively connected with the positive and negative electrodes, and the InGaN absorption layer is partially or completely arranged at the momentDepletion state when visible light signal is incident from the upper n-type GaN ohmic contact layer/window layer to enter into the unintentionally doped In_jGa_1-jAnd an N light absorption layer for generating photo-electron hole pairs, wherein electrons move to the upper positive electrode side and holes move to the lower negative electrode side. Doping of photo-generated holes in Al unintentionally_yGa_1-yN layer and Al_zGa_1-zThe interface of the N composition graded layer is blocked by valence band offset, and hole accumulation is generated, so that Al is generated_zGa_1-zThe potential of the N layer is lowered with respect to its upper and lower layers, i.e., the barrier of this layer to electrons in the N-doped layer below it is lowered, resulting in a large increase in the number of transitions of electrons across the barrier to the upper positive electrode, resulting in a photocurrent gain. Due to Al_zGa_1-zThe hole concentration In the N-component gradient layer is low, the layer is In a fully depleted state under the working voltage (In the range of 0-10V), electrons can rapidly transit the layer and enter the unintentionally doped In_jGa_1-jThe N light absorption layer drifts to the positive electrode under the action of an electric field to finish collection, so that high-speed photoresponse can be realized. In the operation of the detector, electrons and holes both participate in photoresponse, so the detector is a bipolar detector.

Preferably, the substrate is a sapphire, silicon carbide, gallium nitride, aluminum nitride or silicon substrate, the nucleating layer is a low-temperature GaN or AlN nucleating layer with the thickness ranging from 10nm to 35nm, the transition layer is a high-temperature GaN, AlN or AlGaN transition layer with the thickness ranging from 0.2 μm to 3 μm, and the electron concentration of the Si-doped n-type GaN lower ohmic contact layer growing above the transition layer is 3 × 10¹⁷-5×10¹⁸cm^-3The thickness is 0.2-2 μm.

Preferably, the Si is doped with n-type Al_xGa_1-xThe Al component x in the N component gradient layer is linearly and gradually changed, the initial value of x is 0, the end value range is 0.1-0.2, the layer thickness range is 50-200nm, and the electron concentration in the layer is 3 × 10¹⁷-5×10¹⁸cm^-3(ii) a The unintentional doping with Al_yGa_1-yThe Al component y in the N layer is the termination value of x, the thickness is 3-10nm, and the Al is not intentionally doped_zGa_1-zThe Al component z in the N component gradient layer changes linearly, the initial value of z is less than or equal to y, and the end isThe stop value is 0 and the layer thickness is 50-200 nm.

Preferably, the unintentional doping with In_jGa_1-jThe band gap width of the N light absorption layer corresponds to a wavelength range of 400-580 nm, the total thickness is 40-100nm, and the In is not intentionally doped_jGa_1-jA GaN thin insertion layer with the thickness of 1-3nm is arranged in the N light absorption layer every 10-20 nm.

Preferably, the Si is doped with n-type In_kGa_1-kThe In component k In the N component gradient layer is linearly graded, the initial value of k is l, the final value is 0, and the electron concentration range In the layer is 3 × 10¹⁷-5×10¹⁸cm^-3The layer thickness is 10-100 nm.

Preferably, the Si is grown to dope n-type In_kGa_1-kAn ohmic contact layer on Si-doped N-type GaN above the N-component graded layer, wherein the electron concentration range in the layer is 3 × 10¹⁷-5×10¹⁸cm^-3The layer thickness is 30-200 nm.

The invention also aims to provide a preparation method of the bipolar visible light detector, which comprises the following steps:

s1, surface cleaning: organic and inorganic cleaning is adopted to remove impurities and oxide layers on the surface of the wafer;

s2, step manufacturing: manufacturing a mask layer by adopting a standard photoetching technology, and etching to the Si-doped n-type GaN lower ohmic contact layer by adopting a dry etching process or a wet etching process to form a step;

s3, etching damage repair: repairing damage caused by etching on the surface of the wafer by adopting rapid annealing and wet surface treatment;

s4, electrode manufacturing: manufacturing a mask layer by adopting a photoetching technology, forming an annular electrode pattern, depositing a metal electrode, and stripping to obtain two metal ring electrodes on the upper surface and the lower surface of the step; and carrying out alloy annealing treatment on the metal electrode to form ohmic contact.

In step S2 of the present technical solution, the step manufacturing method is implemented by using a dry etching or wet etching process, and the step is etched to the Si-doped n-type GaN lower ohmic contact layer.

Preferably, in step S3, high-temperature rapid annealing is performed in a high-purity nitrogen atmosphere, and then etching damage repair is performed by using an alkaline solution wet process.

Preferably, in step S4, the metal electrode is a combination of metal layers with Ti/Al as the first two layers; the alloy is rapidly annealed at high temperature in a high-purity nitrogen atmosphere or high vacuum.

Preferably, the growth temperature of the GaN thin insertion layer is not intentionally doped with In_jGa_1-jThe N light absorption layers are the same, the GaN thin insertion layer grows In a mode of a pulse V-group N source, and the Si is doped with N-type In_kGa_1-kGrowth temperature of N-component graded layer and unintentional In doping_jGa_1-jThe N light absorption layers are the same, and the growth temperature of the ohmic contact layer on the Si-doped N-type GaN is higher than that of the Si-doped N-type In_kGa_1-kThe N component gradient layer is 200 ℃ higher and 300 ℃ higher. The crystal quality of the GaN thin insertion layer can be further improved by adopting a growing mode of a pulse V group N source.

Compared with the prior art, the invention has the beneficial effects that: the characteristic that GaN and AlGaN materials in III-group nitride have relatively high and stable crystallization quality and the polarization effect of the system material are utilized to form the bipolar photoelectric detector, and the crystallization quality of InGaN in the light absorption layer is improved, so that the bipolar visible light detector has the advantages of high photoelectric gain, high response speed and low working voltage.

Drawings

Fig. 1 is a schematic structural diagram of a bipolar type visible light detector of the present invention.

The figure includes: a substrate-101; a nucleation layer-102; transition layer-103; si-doped n-type GaN lower ohmic contact layer-104; si doped n-type Al_xGa_1-xN component graded layer-105; unintentionally doped with Al_yGa_1-yN layers-106; unintentionally doped with Al_zGa_1-zN component graded layer-107; unintentionally doped with In_jGa_1-jAn N light absorption layer-108; si doped n-type In_kGa_1-kN component graded layer-109; an ohmic contact layer-110 on the Si-doped n-type GaN; a lower ohmic contact electrode-111; an upper ohmic contact electrode-112; step-113.

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.