Photoelectric detector with multi-layer channel p-GaN / AlGaN / n-GaN structure

Abstract

The invention discloses a photoelectric detector with a multi-layer channel p-GaN / AlGaN / n-GaN structure. The photoelectric detector comprises a substrate, a channel layer and a p-type GaN layer which are sequentially stacked from bottom to top and are symmetrical in structure, the channel layer is formed by alternately stacking a plurality of barrier layers and a plurality of n-type GaN layers, namely n-GaN; on the basis of a single-layer p-GaN / AlGaN / n-GaN structure, a plurality of barrier layer / n-GaN layer structures are introduced and stacked below p-GaN to form a multi-layer structure, larger current is formed in a light field through a multi-layer channel, and meanwhile, due to high electron mobility and high saturation drift speed in GaN, the response speed is high; therefore, compared with a single-layer p-GaN / AlGaN / n-GaN device, the GaN / AlGaN / n-GaN device has higher gain bandwidth product and better ultraviolet detection performance, and can better meet the requirement of ultraviolet detection.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device design and photodetector technology, and specifically relates to a multilayer channel p-GaN / AlGaN / n-GaN structure photodetector. Background Technology

[0002] GaN devices based on the third-generation semiconductor material AlGaN / GaN heterojunction have wide applications in aerospace, military defense, and automotive electronics due to their high electron mobility, high electron saturation velocity, and resistance to high temperatures and pressures. Since GaN and its alloys cover the spectral range from red to ultraviolet, devices based on AlGaN / GaN heterojunctions have broad application prospects in photodetection, especially in ultraviolet detection. Among them, enhancement-mode devices based on p-GaN / AlGaN / n-GaN structures have high gain and high on / off current ratio, offering significant advantages in photodetection. Currently, photodetectors based on p-GaN / AlGaN / n-GaN structures mainly rely on the gate voltage in contact with p-GaN to modulate the AlGaN / n-GaN single-channel conductivity; multi-channel photodetector structures are still lacking. For example, patent application CN112349777B discloses a GaN HEMT photodetector with a perovskite composite gate structure and its fabrication method. This structure comprises a perovskite / AlGaN / GaN three-layer structure. By using perovskite as the gate, the conductivity of the two-dimensional electron gas channel of the AlGaN / GaN structure is modulated under illumination to achieve photoelectric response. However, the improvement in conductivity of a single-channel AlGaN / n-GaN is limited. The multi-AlGaN / n-GaN channel structure proposed in this patent application can further enhance the collection process of photogenerated charges based on the single-channel structure, fully realizing the conversion of incident light energy into electrical energy, and improving the photoelectric response sensitivity and detection efficiency of the detector. Furthermore, using a multi-channel structure can increase the thickness of the photosensitive region of the detector, further improving the absorption and conversion efficiency of the p-GaN / AlGaN / n-GaN-based photodetector for wavelengths with deeper penetration. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the present invention aims to provide a multi-channel p-GaN / AlGaN / n-GaN structure photodetector. Based on the p-GaN / AlGaN / n-GaN structure, multiple barrier layers / n-GaN layers are introduced below the p-type GaN layer to form multiple conductive channels, thereby improving the current and photocurrent gain of the p-GaN / AlGaN / n-GaN device. It features higher current gain and faster response speed, and can achieve better detection performance.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A multilayer channel p-GaN / AlGaN / n-GaN structure photodetector includes a substrate 3, a channel layer 2, and a p-type GaN layer 1 stacked sequentially from bottom to top and structurally symmetrical.

[0006] The channel layer 2 is composed of multiple barrier layers 21 and multiple n-type GaN layers, i.e., n-GaN22, stacked alternately.

[0007] A source metal 4 in close contact is provided on one side of the entire channel layer 2, and a drain metal 5 in close contact is provided on the other side. Both the source metal 4 and the drain metal 5 are in close contact with the upper surface of the n-GaN22 at the lowest end of the channel layer 2. The source metal 4 is also in contact with the upper surface of the p-type GaN layer 1. All of the close contacts are ohmic contacts.

[0008] Passivation layers 6 are disposed on the left and right sides of the p-type GaN layer 1, and the passivation layers 6 are located above the channel layer 2.

[0009] The structure of the barrier layer 21 is Al. x Ga 1-x The structure has an N-type barrier layer with a thickness of 8–10 nm and an Al composition x value of 0.2–0.3.

[0010] The barrier layer 21 is AlN, Al x Ga 1-x N and AlN are stacked sequentially from top to bottom, AlN and Al x Ga 1-x The thicknesses of N and AlN are 1nm–3nm, 1nm–500nm, and 1nm–3nm, respectively, and the x-value of Al component is 0.2–0.3.

[0011] The substrate 3 structure is formed by stacking a high-resistivity silicon substrate 32 and a GaN buffer layer 31 from bottom to top.

[0012] The passivation layer 6 is made of silicon dioxide or silicon nitride.

[0013] The p-type GaN layer 1 is p-type doped with a doping concentration of 10. 18 ~10 20 cm -3 The thickness is 50nm to 1μm.

[0014] In the channel layer 2, the barrier layer 21 is undoped, with a thickness of 8–12 nm per layer; the n-GaN22 is n-type doped or undoped, with a doping concentration of less than 10. 16 cm -3 Each layer has a thickness of 20nm to 1μm.

[0015] In use, the source metal 4 is grounded, and ultraviolet light shines down perpendicularly from above the p-type GaN layer 1 onto the device surface. A voltage is applied between the source metal 4 and the drain metal 5, and the drain metal 5 has a current output.

[0016] Compared with monolayer p-GaN / AlGaN / n-GaN devices, the advantages of this invention are:

[0017] (1) Based on the p-GaN / AlGaN / n-GaN structure, this invention introduces multiple barrier layers / n-GaN layers below the p-type GaN layer to form multiple conductive channels. Since the multi-channel p-GaN / AlGaN / n-GaN structure has multiple conductive channels, it can generate a larger current under the same light intensity and the same voltage, thus achieving a higher current gain.

[0018] (2) Since the conductive channels of the present invention are connected in parallel, the electrons of all channels move from the source to the drain almost simultaneously, so the response speed is basically the same as that of a single-layer p-GaN / AlGaN / n-GaN device.

[0019] (3) The present invention can adjust the conduction threshold light intensity of the device by adjusting parameters such as the thickness of the AlGaN barrier layer, the Al composition in AlGaN, and the doping concentration of p-type GaN, and thus adjust the current, gain, response time and other parameters of the device.

[0020] In summary, this invention improves the current and photocurrent gain of p-GaN / AlGaN / n-GaN devices, featuring higher current gain and faster response speed, which better meets the needs of practical ultraviolet detection applications and enables better detection performance. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a photodetector with a multi-channel p-GaN / AlGaN / n-GaN structure.

[0022] Figure 2(a) shows Al x Ga 1-x N-barrier layer structure; Figure 2(b) shows AlN and Al x Ga 1-x N and AlN are stacked sequentially from top to bottom in a structure.

[0023] Figure 1 The labels are: 1-p-type GaN layer, 2-channel layer, 21-barrier layer, 22-n-GaN, 3-substrate, 31-GaN buffer layer, 32-high-resistivity silicon substrate, 4-source metal, 5-drain metal, 6-passivation layer. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] like Figure 1 As shown, a multilayer channel p-GaN / AlGaN / n-GaN structure photodetector includes a substrate 3, a channel layer 2 and a p-type GaN layer 1 stacked sequentially from bottom to top and structurally symmetrical.

[0026] The substrate 3 structure is formed by stacking a high-resistivity silicon substrate 32 and a GaN buffer layer 31 from bottom to top. The high-resistivity silicon substrate 32 has a thickness of 20 μm, and the GaN buffer layer 31 has a thickness of 10 μm.

[0027] The channel layer 2 is composed of three alternating layers of barrier layer 21 / n-GaN22; the structure of barrier layer 21 is shown in Figure 2(a) and Figure 2(b), where Figure 2(a) shows the first structure, which is Al x Ga 1-x The N-type barrier layer structure has a thickness of 8–10 nm; the Al composition x-value is 0.2–0.3; Figure 2(b) shows the second structure, which is AlN and Al x Ga 1-x N and AlN are stacked sequentially from top to bottom, AlN and Al x Ga 1-x The thicknesses of N and AlN are 1 nm, 10 nm, and 1 nm, respectively, and the x-value of Al component is 0.2 to 0.3.

[0028] A source metal 4 in close contact is provided on the left side of the entire channel layer 2, and a drain metal 5 in close contact is provided on the right side. Both the source metal 4 and the drain metal 5 are in close contact with the upper surface of the n-GaN22 at the lowest end of the channel layer 2. The source metal 4 is also in contact with the upper surface of the p-type GaN layer 1. All of the close contacts are ohmic contacts.

[0029] Passivation layers 6 are disposed on the left and right sides of the p-type GaN layer 1, and the passivation layers 6 are located above the channel layer 2. The material of the passivation layer 6 is silicon dioxide or silicon nitride.

[0030] In the absence of light (dark field), the p-type GaN layer 1 depletes the two-dimensional electron gas channel formed by polarization at the interface of the barrier layer 21 / n-type GaN layer 22, and the device is in the off state. When a voltage is applied between the source metal 4 and the drain metal 5, no output current is generated at the drain metal 5. When ultraviolet light is applied, the ultraviolet light is incident on the n-GaN22, generating electron-hole pairs in the n-GaN22, reducing the width of the space charge region, and generating a photogenerated voltage in the pn junction formed by the p-type GaN layer 1 and the n-GaN22. Since the source metal 4 is in contact with the upper end of the p-type GaN layer 1, that is, the gate and the source are short-circuited, the photogenerated voltage regulates the electron concentration in the conductive channel. Under the above two effects, an electron gas channel is formed, and an output current is generated by applying a voltage between the source metal 4 and the drain metal 5.

[0031] The p-type GaN layer 1 is p-type doped with a doping concentration of 10. 18 cm -3 Barrier layer 21 is undoped; n-GaN layer 22 is n-type doped with a doping concentration of 10. 16 cm -3 .

[0032] The p-type GaN layer 1 has a thickness of 70 nm and a width of 6 μm on both sides;

[0033] The barrier layer 21 in the channel layer has a width of approximately 14 μm. If the structure shown in Figure 2(a) is used, the thickness is 10 nm. If the structure shown in Figure 2(b) is used, AlN and Al x Ga 1-x The thicknesses of N and AlN are 1 nm, 10 nm, and 1 nm, respectively. In channel layer 2, except for the bottommost n-GaN layer 22, the thickness of the other n-GaN layers 22 is 20 nm, and the thickness of the bottommost n-GaN layer 22 is 1 μm.

[0034] The source metal 4 forms an ohmic contact with the channel layer and an ohmic contact with the p-type GaN layer 1, and the drain metal 5 forms an ohmic contact with the channel layer.

[0035] Figure 1 The image shows a cross-sectional detail of the photodetector with a multi-channel p-GaN / AlGaN / n-GaN structure. The width of the photodetector perpendicular to this cross-section is 100 μm.

[0036] The basic detection principle and process of this invention are as follows:

[0037] In its barrier layer / n-GaN structure, due to the piezoelectric polarization and spontaneous polarization of AlGaN and the spontaneous polarization of GaN, a high-concentration two-dimensional electron gas with a density on the order of 10-1 is formed at the barrier layer / n-GaN interface.13 cm -2 The concentration is on the order of 10 19 cm -3 Or even higher. In this detector, heavily doped p-type GaN is introduced above the uppermost barrier layer. The p-type GaN forms a pn junction with n-GaN, depleting the two-dimensional electron gas beneath the p-type GaN. Since the doping concentration of p-type GaN is much higher than that of n-GaN, it can deplete all the n-GaN layers in the channel region. Without light, the portion of the two-dimensional electron gas channel below the p-type GaN is depleted; when a voltage is applied between the source and drain, the device does not conduct. In use:

[0038] (1) Ultraviolet light shines down perpendicularly to the upper surface of the detector from above the p-type GaN layer 1. Since the barrier layer 21 does not absorb ultraviolet light and the absorption depth of the GaN layer for ultraviolet light is 390 nm, all n-GaN layers 22 will absorb ultraviolet light. Through the absorption of ultraviolet light by the n-GaN layer 22, electron-hole pairs are generated in the n-GaN layer 22. The electron-hole pairs will narrow the space charge region under the p-type GaN layer 1.

[0039] (2) Since the upper surface of the p-type GaN layer 1 is shorted to the source metal 4, the photogenerated voltage generated in the pn junction formed by the p-type GaN layer 1 and the n-GaN layer 22 will be similar to the electron concentration at the interface of the gate voltage control barrier layer 21 / n-GaN layer 22 of the MOSFET.

[0040] Under the above two effects, a conductive channel will be formed at the interface of the barrier layer 21 / n-GaN layer 22. By applying a 5V voltage between the drain metal 5 and the source metal 4, an output current can be formed on the drain metal 5.

[0041] Compared to single-layer p-GaN / AlGaN / n-GaN devices, the advantages of this embodiment are: the detector has three conductive channels, which allows for a larger output current and thus higher gain compared to single-layer p-GaN / AlGaN / n-GaN devices. Simultaneously, due to the high electron mobility and high electron saturation velocity of GaN material, the ultraviolet detector exhibits a very high response speed after illumination. Therefore, compared to single-layer p-GaN / AlGaN / n-GaN devices, this invention has a higher gain-bandwidth product and better ultraviolet detection performance.

[0042] In summary, based on a single-layer p-GaN / AlGaN / n-GaN structure, this invention utilizes a multi-layer channel p-GaN / AlGaN / n-GaN structure formed by stacking multiple barrier layers / n-GaN units to achieve higher current gain and higher response speed under an optical field, thus providing better ultraviolet detection performance.

Claims

1. A photodetector with a multi-channel p-GaN / AlGaN / n-GaN structure, characterized in that, It includes a substrate (3), a channel layer (2), and a p-type GaN layer (1) stacked sequentially from bottom to top and with a symmetrical structure. The channel layer (2) is composed of multiple barrier layers (21) and multiple n-type GaN layers, i.e., n-GaN (22), stacked alternately; A source metal (4) in close contact is provided on one side of the entire channel layer (2), and a drain metal (5) in close contact is provided on the other side. Both the source metal (4) and the drain metal (5) are in close contact with the upper surface of the n-GaN (22) at the lowest end of the channel layer (2). The source metal (4) is also in contact with the upper surface of the p-type GaN layer (1). All of the close contacts are ohmic contacts. Passivation layers (6) are provided on the left and right sides of the p-type GaN (1), and the passivation layers (6) are located above the channel layer (2).

2. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, The structure of the barrier layer (21) is Al x Ga 1-x The structure has an N-type barrier layer with a thickness of 8–10 nm and an Al composition x value of 0.2–0.

3.

3. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, The barrier layer (21) is AlN, Al x Ga 1-x N and AlN are stacked sequentially from top to bottom, AlN and Al x Ga 1-x The thicknesses of N and AlN are 1nm–3nm, 1nm–500nm, and 1nm–3nm, respectively, and the x-value of Al component is 0.2–0.

3.

4. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, The substrate (3) structure is formed by stacking a high-resistivity silicon substrate (32) and a GaN buffer layer (31) from bottom to top.

5. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, The passivation layer (6) is made of silicon dioxide or silicon nitride.

6. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, The p-type GaN layer (1) is p-type doped with a doping concentration of 10. 18 ~10 20 cm -3 The thickness is 50nm to 1μm.

7. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, In the channel layer (2), the barrier layer (21) is undoped, with a thickness of 8-12 nm per layer; the n-GaN (22) is n-type doped or undoped, with a doping concentration of less than 10. 16 cm -3 Each layer has a thickness of 20nm to 1μm.

8. A photodetector with a multilayer channel p-GaN / AlGaN / n-GaN structure according to claim 1, characterized in that, In use, the source metal (4) is grounded, and ultraviolet light shines down perpendicularly from above the p-type GaN layer (1) onto the device surface. A voltage is applied between the source metal (4) and the drain metal (5), and the drain metal (5) has a current output.

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