CN109119508B - Back incidence solar blind ultraviolet detector and preparation method thereof - Google Patents

Abstract

The invention discloses a back incidence solar blind ultraviolet detector and a preparation method thereof, wherein a back incidence structure is adopted, and the device comprises: the invention aims to solve the problems that an AlGaN-based p-i-n junction ultraviolet detector is low in p-type doping efficiency, thin film cracks, an epitaxial structure needs to be optimized, the crystal quality is low and the like.

Description

A back-incidence sun-blind ultraviolet detector and its preparation method

Technical field

The present invention relates to the field of photoelectric detectors, and in particular to back-incidence solar blind ultraviolet detectors and preparation methods thereof.

Background technique

Sunblind UV detectors can detect ultraviolet light and convert the detected ultraviolet light into easily identifiable electrical signals for transmission. Sun-blind ultraviolet detectors have the advantages of high quantum efficiency, high sensitivity, stable performance, low background noise, not easily interfered by radiation and chemicals, and wide detection range. They are currently used in missile guidance and early warning, fire alarm, communications, and solar astronomy research. It has been widely used in many military and civilian fields, especially in places with weak ultraviolet signals. Its advantages of high detection sensitivity and high accuracy are particularly prominent.

In the existing sun-blind UV detector preparation technology, there are three main preparation materials: 4H-SiC, MgZnO, and GaN/AlGaN. Different sun-blind UV detectors made of these three materials each have their own advantages and disadvantages. The 4H-SiC sun-blind UV detector has a high melting point and good thermal conductivity, and is suitable for working at high temperatures and high energies. However, it has the disadvantages of low quantum efficiency and unadjustable band gap; MgZnO-type sun-blind UV detector single crystal substrate It has the advantages of matching, non-toxic and harmless, simple synthesis, low cost, fast electron saturation and drift speed, wide and adjustable band gap, etc., but there is currently a lack of corresponding packaging technology; chemical properties of GaN/AlGaN sun-blind UV detectors It is stable, difficult to interfere with radiation, can be doped with Al to adjust the band gap, has good detection performance, and has a fast response speed. However, it has shortcomings such as high growth temperature and difficult substrate matching.

The related technologies for preparing solar-blind UV detectors have developed so far. GaN/AlGaN is currently the best preparation material and is the most widely used in wide-bandgap UV detectors. In the AlGaN-based p-i-n junction UV detector, the p-region improves the sensitivity of ultraviolet light, making it easier to absorb and excite electron-hole pairs in the i-layer to form carriers and transit in a short time. The p-i-n junction of the detector can greatly improve its detection capability, generate more carriers, and speed up the carrier speed. The i-layer prevents the base material from affecting the breakdown voltage. The responsivity, response time and quantum efficiency of the device are all improved. has been improved. Although AlGaN-based p-i-n junction UV detectors have many advantages, there are also some disadvantages: when Al ions are injected to prepare AlGaN with a high Al component, AlGaN will conflict with the sapphire substrate, causing damage to the crystal lattice and thermal mismatch. This results in high dislocation density and film cracks; p-type doping efficiency is not high.

Contents of the invention

The purpose of the invention is to solve the problems of low p-type doping efficiency, film cracks, epitaxial structure to be optimized, and low crystal quality of AlGaN-based p-i-n junction ultraviolet detectors, and to provide a device with low dark current, higher quantum efficiency, and better suppression ratio. A back-incidence sun-blind ultraviolet detector with better detection rate and better performance and its preparation method.

The technical solution adopted by the present invention: a back-incident sun-blind ultraviolet detector, including: a substrate, a buffer layer, a stress relief layer, an n-type ohmic contact layer, an n-type transition layer, an i-type light absorption layer, a p-type doped Hybrid layer, p-type transition layer, p-type ohmic contact layer, protective layer, n-type electrode, p-type electrode;

The substrate is a sapphire substrate, located at the bottom of each layer;

The buffer layer is a high-temperature AlN layer with a thickness of 350nm, which is used to control stress accumulation and prevent film cracks, and is located on the substrate;

The stress release layer is an AlN/Al _0.6 Ga _0.4 N superlattice layer, which is used to reduce the dislocation density of the epitaxial structure and is located above the buffer layer;

The n-type ohmic contact layer is composed of Al _0.6 Ga _0.4 N doped with Si, has a thickness of 550nm, and is located on the stress release layer;

_The n _- type transition layer is composed of Al It avoids sudden changes in the Al component and improves the carrier collection rate. This layer is located above the n-type ohmic contact layer;

The i-type light absorption layer is 200nm thick, composed of undoped Al _0.45 Ga _0.55 N, and is located above the n-type transition layer;

The p-type doped layer is 75nm thick, composed of Mg-doped Al _0.45 Ga _0.55 N, and is located on the i-type light absorption layer;

The p-type transition _layer is composed of Mg _- doped Al 25nm, located above the p-type doped layer;

The p-type ohmic contact layer is 50nm thick, formed of Mg-doped GaN, and is located above the p-type transition layer;

The protective layer is a SiO ₂ layer, 200nm thick, covering the upper surface of the entire device except for the two electrodes;

The n-type electrode shown is annular and located on the edge of the n-type ohmic contact layer;

The p-type electrode is located on the p-type ohmic contact layer.

The preparation method of a back-illuminated solar blind ultraviolet detector of the present invention is as follows:

Substrate epitaxial wafer cleaning: soak the epitaxial wafer in acetone, use ultrasonic cleaning for 10 minutes while soaking, then use alcohol immersion and ultrasonic cleaning for 10 minutes, then deionize and clean the organic matter adsorbed on the epitaxial wafer, and then soak the epitaxial wafer in hydrochloric acid Leave in the solution for 5 minutes and then rinse with deionization.

Make the buffer layer and stress relief layer: On the substrate, use the metal organic compound chemical vapor deposition method to epitaxially grow the buffer layer at a high temperature of 1100°C, and then grow the buffer layer on the buffer layer at 1200°C and a III/V flow rate of 1000 Ratio and reaction chamber pressure between 10Pa and 15Pa, epitaxial growth forms a stress relief layer.

Make an n-type ohmic contact layer: Use metal organic compound chemical vapor deposition method on the stress relief layer to grow and form an n-type ohmic contact layer.

Make the transition layer: Al ions are injected multiple times. Each time, Al ions are injected into the transition layer with different energies and doses according to the needs. Gradually and slowly change the injection conditions of Al ions, thereby changing the Al ions at different positions in the n-type transition layer and p-type transition layer. The content of the component causes the Al component to change slowly and reduce the change gradient of the Al component. As needed, the number of injections is 5 to 10 times, the injection energy is 10keV to 100keV, and the injection dose is 2×10 ¹³ ions/cm ² To 1×10 ¹⁴ ions/cm ² , an n-type transition layer and a p-type transition layer are grown on the n-type ohmic contact layer and the p-type doped layer respectively.

Make the i-type light absorbing layer and p-type doped layer: Use the metal organic compound chemical vapor deposition method on the n-type transition layer to grow sequentially to form the i-type light absorbing layer and p-type doped layer.

Preparation of p-type ohmic contact layer: Use metal organic compound chemical vapor deposition method to grow and form a p-type ohmic contact layer on top of the p-type transition layer.

Preparation of protective layer: Plasma-enhanced chemical vapor deposition is used to prepare the SiO ₂ protective layer of the device, which has the functions of passivation and improving device performance and reliability.

Mesa etching: using ICP process, its ICP power is 300W, RF power is 100W, Cl ₂ /BCl ₃ flow ratio is 0.8 (ml/s)/0.1 (ml/s) under standard condition, SiO ₂ mask, The chamber pressure is 12 to 15 Pa. After etching, boiling potassium hydroxide solution is used to treat the device to reduce the adverse effects caused by etching.

Preparation of electrodes: n-type electrode is a Ti/Al/Ni/Au sequence alloy, p-type electrode is a Ni/Au sequence double-layer metal, and photolithography and electron beam evaporation are used to remove the n-type ohmic contact layer and p-type ohmic contact layer A protective layer is formed on part of the contact layer to leave a place for installing n-type electrodes and p-type electrodes. Electron beam evaporation is then used to deposit n-type electrodes and p-type electrodes at corresponding positions. Finally, the n-type electrode and p-type electrode are deposited in nitrogen at 700°C. Medium rapid annealing for 1 minute.

Beneficial effects of the present invention: (1) The existence of the buffer layer suppresses film cracking to a certain extent. (2) The use of a back-illuminated structure avoids the problem of low doping efficiency of the p-type layer, and thicker metal can be used to produce a p-type ohmic contact layer with lower resistance. (3) The existence of the stress relief layer allows the dislocation density in the epitaxial structure to be controlled. (4) The electrode connection is more stable and reliable, and rapid degradation of the electrodes greatly reduces the resistance of the two electrodes. (5) The low Al composition gradient of the two transition layers improves device performance.

Description of the drawings

Figure 1 is a schematic cross-sectional structural diagram of the present invention.

Figure 2 is a schematic top view of the structure of the present invention.

In the figure: 1-substrate, 2-buffer layer, 3-stress release layer, 4-n-type ohmic contact layer, 5-n-type transition layer, 6-i-type light absorption layer, 7-p-type doped layer, 8—p-type transition layer, 9—p-type ohmic contact layer, 10—protective layer, 11—n-type electrode, 12—p-type electrode.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

The present invention adopts a back-illuminated structure, as shown in Figure 1. The device of the present invention includes: substrate (1), buffer layer (2), stress release layer (3), n-type ohmic contact layer (4), n-type transition layer layer (5), i-type light absorption layer (6), p-type doped layer (7), p-type transition layer (8), p-type ohmic contact layer (9), protective layer (10), n-type electrode ( 11), p-type electrode (12), the substrate (1) is a sapphire substrate, located at the bottom of each layer; the buffer layer (2) is a high-temperature AlN layer with a thickness of 350nm, used to control stress accumulation and prevent Film cracks are located on the substrate (1); the stress release layer (3) is an AlN/Al _0.6 Ga _0.4 N superlattice layer. The function of this layer is to reduce the dislocation density of the epitaxial structure and is located Above the buffer layer (2); the n-type ohmic contact layer (4) is composed of Al _0.6 Ga _0.4 N doped with Si, has a thickness of 550 nm, and is located above the stress release layer (3); the n _Type transition layer (5) _is composed of Al 0.45, this layer avoids sudden changes in the Al component and improves the carrier collection rate. This layer is located above the n-type ohmic contact layer (4); the i-type light absorption layer (6) is 200nm thick and consists of It is composed of doped Al _0.45 Ga _0.55 N and is located on the n-type transition layer (5); the p-type doped layer (7) is an Al _0.45 Ga _0.55 N layer doped with Mg, is 75nm thick, and is located on i On top of _the type light absorbing layer (6 ₎ ; the p-type transition layer (8) is composed of Al On top of the doping layer (7); the p-type ohmic contact layer (9) is 50nm thick, composed of Mg-doped GaN, and is located on the p-type transition layer (8); the protective layer (10) is SiO ₂ layer, 200nm thick, covering the upper surface of the entire device except for the n-type electrode (11) and p-type electrode (12); the n-type electrode (11) shown is annular and located at the n-type ohmic contact layer (4) Above the edge; the p-type electrode (12) is located on the p-type ohmic contact layer (9).

Part of the preparation method of the present invention is the same as the conventional preparation method, but other parts are optimized:

The preparation process steps include: cleaning the substrate (1) epitaxial wafer, making the buffer layer (2) and the stress relief layer (3), making the n-type ohmic contact layer (4), making the transition layer, and making the i-type light absorption layer (6 ) and p-type doping layer (7), making p-type ohmic contact layer (9), making protective layer (10), mesa etching, making electrodes, in which the substrate (1) epitaxial wafer is cleaned, made transition layer, prepared The processes of protective layer, mesa etching, electrode preparation, and transition layer preparation are optimized in the present invention.

Substrate (1) Epitaxial wafer cleaning: soak the epitaxial wafer in acetone, use ultrasonic cleaning for 10 minutes while soaking, then use alcohol immersion and ultrasonic cleaning for 10 minutes, and then deionize and clean the organic matter adsorbed on the epitaxial wafer, and then clean the epitaxial wafer Soak in hydrochloric acid solution for 5 minutes, then rinse with deionization.

Preparing the buffer layer (2) and the stress relief layer (3): On the substrate (1), use the metal organic compound chemical vapor deposition method to epitaxially grow the buffer layer (2) at a high temperature of 1100°C, and then epitaxially grow the buffer layer (2). The stress relief layer (3) is epitaxially grown on the chip at 1200°C, a III/V flow ratio of 1000, and a reaction chamber pressure between 10 Pa and 15 Pa.

Make the n-type ohmic contact layer (4): Use the metal-organic compound chemical vapor deposition method on the stress relief layer (3) to grow and form the n-type ohmic contact layer (4).

Make the transition layer: Al ions are injected multiple times. Each time, Al ions are injected into the transition layer with different energies and doses according to the needs. Gradually and slowly change the injection conditions of Al ions, thereby changing the n-type transition layer (5) and p-type transition layer ( 8) The content of the Al component at different positions in the Al component changes slowly and reduces the gradient of the Al component. As needed, the number of injections is 5-10 times, the injection energy is 10keV to 100keV, and the injection dose is 2× 10 ¹³ ions/cm ² to 1×10 ¹⁴ ions/cm ² , respectively grown on the n-type ohmic contact layer (4) and p-type doped layer (7) to form an n-type transition layer (5) and a p-type transition layer Layer(8).

Make the i-type light absorption layer (6) and the p-type doped layer (7): Use the metal organic compound chemical vapor deposition method on the n-type transition layer (5) to grow sequentially to form the i-type light absorption layer (6) and p-type doping layer (7). type doped layer (7).

Preparing the p-type ohmic contact layer (9): Use the metal organic compound chemical vapor deposition method to grow and form the p-type ohmic contact layer (9) on the p-type transition layer (8).

Preparing the protective layer (10): Plasma-enhanced chemical vapor deposition (PECVD) is used to prepare the SiO ₂ protective layer (10) of the device, which has the functions of passivation and improving device performance and reliability.

Mesa etching: using ICP process, its ICP power is 300W, RF power is 100W, Cl ₂ /BCl ₃ flow ratio is 0.8 (ml/s)/0.1 (ml/s) under standard condition, SiO ₂ mask, The chamber pressure is 12-15Pa. After etching, boiling potassium hydroxide solution is used to treat the device to reduce the adverse effects caused by etching.

Make the electrodes: the n-type electrode (11) is a Ti/Al/Ni/Au sequence alloy, and the p-type electrode (12) is a Ni/Au sequence double-layer metal. Use photolithography and electron beam evaporation to remove the n-type ohmic layer. The protective layer (10) on part of the contact layer (4) and the p-type ohmic contact layer (9) is used to leave a place for installing the n-type electrode (11) and the p-type electrode (12), and then is deposited by electron beam evaporation. The n-type electrode (11) and p-type electrode (12) were deposited at corresponding positions, and finally rapidly annealed in nitrogen at 700°C for 1 minute.

Claims (10)

1. A back-incidence solar blind ultraviolet detector, including: substrate (1), buffer layer (2), stress release layer (3), n-type ohmic contact layer (4), n-type transition layer (5), i-type light absorption layer (6), p-type doped layer (7), p-type transition layer (8), p-type ohmic contact layer (9), protective layer (10), n-type electrode (11), p-type Electrode (12), the substrate (1) is a sapphire substrate, located at the bottom of each layer; the buffer layer (2) is a high-temperature AlN layer, located above the substrate (1); the stress release layer ( 3) is an AlN/Al _0.6 Ga _0.4 N superlattice layer located on the buffer layer (2); the n-type ohmic contact layer (4) is composed of Al _0.6 Ga _0.4 N doped with Si and is located on the stress On top of the release layer (3); the n-type transition layer (5) is composed of Al _x Ga _1-x N, which is located on the n-type ohmic contact layer (4); the i-type light absorption layer (6 ) is composed of undoped Al _0.45 Ga _0.55 N and is located on the n-type transition layer (5); the p-type doped layer (7) is composed of Mg-doped Al _0.45 Ga _0.55 N and is located on i on the p-type light absorbing layer (6); the p-type transition layer (8) is composed of Mg-doped AlGaN and is located on the p-type doped layer (7); the p-type ohmic contact layer (9) It is composed of Mg-doped GaN and is located on the p-type transition layer (8); the protective layer (10) is a SiO ₂ layer, which covers the n-type electrode (11) and p-type electrode (12) on the upper surface of the entire device ); the n-type electrode (11) is ring-shaped and is located on the edge of the n-type ohmic contact layer (4); the p-type electrode (12) is located on the p-type ohmic contact layer (9) . 2. A back-incidence sun-blind ultraviolet detector according to claim 1, characterized in that: the thickness of the buffer layer (2) is 350 nm. 3. A back-incidence sun-blind ultraviolet detector according to claim 1, characterized in that: the thickness of the n-type ohmic contact layer (4) is 550nm. 4. A back-incident sun-blind ultraviolet detector according to claim 1, characterized in that: the n-type transition layer (5) is 20 nm thick, the Al composition of this layer changes, and is made of n-type ohmic contact. Gradient from 0.6 for layer (4) to 0.45 for i-type light absorbing layer (6). 5. A back-incidence solar blind ultraviolet detector according to claim 1 or 4, characterized in that: the i-type light absorption layer (6) is 200nm thick. 6. A back-incidence sun-blind ultraviolet detector according to claim 1, characterized in that: the p-type doped layer (7) is 75 nm thick. 7. A back-incident sun-blind ultraviolet detector according to claim 1, characterized in that: the Al component of the p-type transition layer (8) gradually decreases from 0.45 to 0, from close to the p-type doped layer (7) gradually decreases toward the p-type ohmic contact layer (9), with a thickness of 25nm. 8. A back-incidence sun-blind ultraviolet detector according to claim 1, characterized in that: the p-type ohmic contact layer (9) is 50 nm thick. 9. A back-illuminated solar blind ultraviolet detector according to claim 1, characterized in that the protective layer (10) is 200nm thick. 10. A method for preparing a back-illuminated solar blind ultraviolet detector, which is characterized by: Substrate (1) Epitaxial wafer cleaning: soak the epitaxial wafer in acetone, use ultrasonic cleaning for 10 minutes while soaking, then use alcohol immersion and ultrasonic cleaning for 10 minutes, and then deionize and clean the organic matter adsorbed on the epitaxial wafer, and then clean the epitaxial wafer Soak in hydrochloric acid solution for 5 minutes, then rinse with deionization; Preparing the buffer layer (2) and stress relief layer (3): On the substrate (1), use the metal organic compound chemical vapor deposition method to epitaxially grow the buffer layer (2) at a high temperature of 1100°C, and then grow the buffer layer (2) on the substrate (1). The stress release layer (3) is epitaxially grown on the layer (2) at 1200°C, a III/V flow ratio of 1000, and a reaction chamber pressure between 10 Pa and 15 Pa; Make the n-type ohmic contact layer (4): Use metal organic compound chemical vapor deposition method on the stress relief layer (3) to grow and form the n-type ohmic contact layer (4); Make the transition layer: Al ions are injected multiple times. Each time, Al ions are injected into the transition layer with different energies and dosages as needed. Gradually and slowly change the injection conditions of Al ions, thereby changing the n-type transition layer (5) and p-type transition layer ( 8) The content of the Al component at different positions in the medium causes the Al component to change slowly and reduce the gradient of the Al component. As needed, the number of injections is 5 to 10 times, the injection energy is 10keV to 100keV, and the injection dose is 2× 10 ¹³ ions/cm ² to 1×10 ¹⁴ ions/cm ² , respectively grown on the n-type ohmic contact layer (4) and p-type doped layer (7) to form an n-type transition layer (5) and a p-type transition layer layer(8); Make the i-type light absorption layer (6) and p-type doped layer (7): Use the metal organic compound chemical vapor deposition method on the n-type transition layer (5) to grow sequentially to form the i-type light absorption layer (6) and p-type doping layer (7). type doped layer (7); Preparing the p-type ohmic contact layer (9): Use the metal organic compound chemical vapor deposition method to grow and form the p-type ohmic contact layer (9) on the p-type transition layer (8); Preparing the protective layer (10): Plasma-enhanced chemical vapor deposition is used to prepare the SiO ₂ protective layer (10) of the device, which has the functions of passivation and improving device performance and reliability; Mesa etching: using ICP process, its ICP power is 300W, RF power is 100W, Cl ₂ / BCl ₃ flow ratio is 0.8 (ml/s) / 0.1 (ml/s) under standard condition, SiO ₂ mask, The cavity pressure is 12Pa to 15Pa. After etching, boiling potassium hydroxide solution is used to treat the device to reduce the adverse effects caused by etching; Make electrodes: n-type electrode (11) is a Ti/Al/Ni/Au sequence alloy, and p-type electrode (12) is a Ni/Au sequence double-layer metal. Use photolithography and electron beam evaporation to remove the n-type ohmic layer. The protective layer (10) on part of the contact layer (4) and the p-type ohmic contact layer (9) is used to leave a position for installing the n-type electrode (11) and the p-type electrode (12), and then is deposited by electron beam evaporation. The n-type electrode (11) and p-type electrode (12) were deposited at corresponding positions, and finally rapidly annealed in nitrogen at 700°C for 1 minute.