Algan / gan transistor with p-i-n gate structure and preparation method thereof

Abstract

The application discloses an AlGaN / GaN transistor with a P-I-N gate structure and a preparation method thereof, and belongs to the technical field of semiconductor devices. x Ga 1‑x N potential barrier layer, wherein 0 < x < 1; the transistor further comprises a P-I-N gate structure located on the Al x Ga 1‑x N potential barrier layer, and a source and a drain respectively arranged on the Al x Ga 1‑x N potential barrier layer and located on both sides of the P-I-N gate structure; the P-I-N gate structure comprises, from bottom to top, a p-type GaN layer, an intrinsic i-GaN layer and an n-type GaN layer in sequence. The transistor can exhibit extremely high light responsivity under ultraviolet light irradiation, and has great application potential in the field of high-sensitivity detection and imaging in the solar blind ultraviolet band.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and particularly relates to an AlGaN / GaN transistor with a P-I-N gate structure and a preparation method thereof. Background Art

[0002] Due to its excellent material properties, such as a wide direct bandgap, a high breakdown field strength, and a high electron saturation velocity, the AlGaN / GaN heterojunction is an ideal platform for fabricating high-performance ultraviolet photodetectors and power electronic devices. The high electron mobility transistor (HEMT) based on this heterojunction can utilize the high-concentration two-dimensional electron gas (2DEG) at its interface to achieve a high-conductivity channel.

[0003] In power switch applications, enhancement-mode (normally-off) devices are crucial for simplifying circuit design and improving system safety. The p-GaN gate technology is one of the mainstream solutions to achieve enhancement-mode AlGaN / GaN HEMTs, which realizes the normally-off characteristic by depleting the underlying 2DEG with a p-type GaN layer. However, traditional p-GaN gate HEMTs usually face problems such as a low threshold voltage and limited gate reliability. In terms of photodetection applications, although the AlGaN / GaN HEMT structure itself has ultraviolet light response, its photoelectric conversion efficiency (responsivity) still has a large room for improvement. How to improve the threshold voltage, gate reliability of HEMTs and their responsivity as photodetectors simultaneously without significantly increasing the process complexity is the current technical challenge. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an AlGaN / GaN transistor (PIN-HEMT) with a P-I-N gate structure and a preparation method thereof, which solves the problems in the prior art.

[0005] The purpose of the present invention can be achieved by the following technical solutions: An AlGaN / GaN transistor with a P-I-N gate structure includes, from bottom to top in sequence: a substrate, a GaN buffer layer, a GaN channel layer, and an Al x Ga 1-x GaN barrier layer, where 0 < x < 1; characterized in that the transistor further includes a P-I-N gate structure located on the Al x Ga 1-x GaN barrier layer, and source and drain electrodes respectively disposed on the Al x Ga 1-x GaN barrier layer and on both sides of the P-I-N gate structure; The P-I-N gate structure includes, from bottom to top in sequence: a p-type GaN layer, an intrinsic i-GaN layer, and an n-type GaN layer.

[0006] Furthermore, the Al x Ga 1-x In the N-barrier layer, x is 0.2 and the thickness is 25nm; Furthermore, the GaN channel layer has a thickness of 200 nm.

[0007] Furthermore, in the PIN gate structure: the thickness of the p-type GaN layer is 100 nm, and the Mg doping concentration is 1 × 10⁻⁶. 18 cm -3 The intrinsic i-GaN layer has a thickness of 30 nm and is an undoped layer; the n-type GaN layer has a thickness of 30 nm and a Si doping concentration of 5 × 10⁻⁶. 16 cm -3 .

[0008] Furthermore, the source and drain are formed on the Al x Ga 1-x Ti / Al / Ni / Au multilayer metal ohmic contact electrode on N-barrier layer.

[0009] The above-mentioned method for fabricating an AlGaN / GaN transistor with a PIN gate structure includes the following steps: S1, GaN buffer layer, GaN channel layer and Al are epitaxially grown sequentially on the substrate. x Ga 1-x N-barrier layer; then in Al x Ga 1-x An epitaxial stacked structure is formed by sequentially growing a p-type GaN layer, an intrinsic i-GaN layer, and an n-type GaN layer on an N-barrier layer. S2, at both sides of the epitaxial stacked structure, is etched from the n-type GaN layer down to Al using inductively coupled plasma dry etching. x Ga 1-x An N-barrier layer is formed to create the PIN gate structure; S3, perform mesa isolation etching on the epitaxial stacked structure containing the PIN gate structure to define the active region of the transistor; S5, the source and drain are fabricated on the AlxGa1-xN barrier layers located on both sides of the PIN gate structure.

[0010] Furthermore, when fabricating the source and drain electrodes, electron beam evaporation is used to deposit the source and drain metals, and thermal annealing is performed to form ohmic contacts.

[0011] An ultraviolet photodetector includes the aforementioned AlGaN / GaN transistor with a PIN gate structure.

[0012] Furthermore, the source and drain of the transistor are configured as the photoelectric signal output terminals of the ultraviolet photodetector; the channel of the transistor and the portion located in the Al x Ga 1-x The region above the N-barrier layer is configured as a photosensitive region for receiving incident ultraviolet light.

[0013] The above-mentioned AlGaN / GaN transistors with PIN gate structure are used in solar-blind ultraviolet detection and imaging.

[0014] The beneficial effects of this invention are: 1. This invention overcomes the design limitations of a single p-GaN gate by sequentially epitaxially introducing an intrinsic i-GaN layer and an n-GaN layer on top of the p-GaN layer in the gate region, thus constructing a composite PIN junction gate structure. In this special stacking scheme, the PIN junction not only introduces additional band modulation and built-in potential, but its internal i-GaN layer also serves as a physical buffer and carrier modulation layer, significantly optimizing the device's photoelectric response characteristics under illumination conditions. This structure significantly enhances the photogenerated electromotive force by strengthening the built-in electric field, expanding the depletion region width, and improving the separation and collection efficiency of photogenerated carriers. Simultaneously, the introduction of the intermediate i-GaN layer effectively suppresses dark current and carrier recombination losses. This combination of composite band design and physical modulation mechanism enables the device to achieve not only a higher photogenerated electromotive force output but also significantly improved gate withstand voltage and stability, fundamentally enhancing its operational reliability in high-voltage gate driving and high-sensitivity photodetector applications.

[0015] 2. This invention applies the aforementioned PIN composite gate structure to an ultraviolet photodetector, forming a bandgap coupling with the bottom AlGaN / GaN heterojunction. When irradiated with ultraviolet light, the built-in electric field within the composite gate region efficiently separates the excited photogenerated carriers, causing a large number of photogenerated holes to be directionally swept and accumulated in the p-GaN layer. This "point-to-point accumulation" of holes produces an equivalent "forward gate voltage" effect, significantly altering the bandgap state at the p-GaN and AlGaN barrier layer interface, thereby drastically reducing the depletion effect on the bottom two-dimensional electron gas (2DEG) and causing the conductivity of the bottom channel to be released instantaneously. This results in extremely high photocurrent gain for the device, achieving a gain as high as 10⁻¹⁰ with extremely low dark current. 9 Its photocurrent switching ratio is excellent. Its ultraviolet responsivity reaches 7.04 × 10⁻⁶. 7 A / W achieves a disruptive improvement of more than eight orders of magnitude compared to traditional p-GaN gate structures. 3. The method provided by this invention does not employ complex patterning techniques that require secondary masking, etching, and secondary growth, nor does it use novel or unusual materials that are difficult to match with existing semiconductor production lines. Instead, this solution directly relies on the standard metal-organic chemical vapor deposition (MOCVD) process. After the growth of the underlying structure is completed, i-GaN and n-GaN layers are continuously epitaxially grown to complete the construction of the core PIN stack. This gives the high-performance detector excellent industrial compatibility. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a cross-sectional schematic diagram of the PIN-HEMT device structure of the present invention; Figure 2 This is a schematic diagram of the band structure of the PIN-HEMT of the present invention under darkness and ultraviolet light. Figure 3 This is a schematic diagram illustrating the carrier transport principle of the PIN-HEMT as a photosensitive element in an ultraviolet photodetector during operation. Figure 4 The output characteristic curves of the PIN-HEMT as the photosensitive element of the ultraviolet photodetector of the present invention under illumination and dark conditions are shown. Figure 5 This is a schematic cross-sectional view of the P-GaN device structure with different gate thicknesses according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention proposes an AlGaN / GaN transistor (PIN-HEMT) with a PIN gate structure, whose epitaxial structure, from bottom to top, includes a substrate, a GaN buffer layer, a GaN channel layer, and an Al... x Ga 1-x N-barrier layer. In Al x Ga 1-xOn the N-type barrier layer, a p-type GaN layer, an intrinsic GaN (i-GaN) layer, and an n-type GaN (n-GaN) layer are grown sequentially. These three layers together constitute the PIN gate structure of the device. The source and drain are fabricated on Al atoms on both sides of the gate (both sides of the PIN gate structure). x Ga 1-x On the N-barrier layer.

[0020] In some embodiments: the p-type GaN layer has a thickness of 100 nm and a doping concentration (Mg) of 1 × 10⁻⁶. 18 cm -3 The i-GaN layer has a thickness of 30 nm and a doping concentration (Si) of 1 × 10⁻⁶. 16 cm -3 The n-GaN layer has a thickness of 30 nm and a doping concentration (Si) of 5 × 10⁻⁶. 16 cm -3 .

[0021] The Al x Ga 1-x The N-barrier layer has an Al composition of x=0.2, a thickness of 25 nm, and a doping concentration of 1×10⁻⁶. 16 cm -3 The GaN channel layer has a thickness of 200 nm and a doping concentration of 1 × 10⁻⁶. 16 cm -3 ; Specific structure as follows Figure 1 As shown.

[0022] The substrate is selected from sapphire, SiC or silicon.

[0023] The following examples will provide a detailed description; Example 1 This embodiment describes PIN-HEMT devices (such as...) Figure 1 The preparation method of (shown) includes the following steps: S1: Provide a substrate (silicon), and use metal-organic chemical vapor deposition (MOCVD) technology to sequentially epitaxially grow (deposition temperature 1080°C) a GaN buffer layer (2-3μm) and a GaN channel layer (200nm, Si doping concentration 1×10⁻⁶). 16 cm -3 Al 0.2 Ga 0.8 N-type barrier layer (25nm, unintentionally doped, background concentration approximately 1×10⁻⁶) 16 cm -3 Then, at approximately 900°C under a nitrogen atmosphere, using Cp₂Mg as the doping source in Al… 0.2 Ga 0.8A 100 nm p-GaN layer is grown on the N-barrier layer, with a magnesium doping concentration of approximately 1 × 10⁻⁶. 18 cm -3 Subsequently, the magnesium source was turned off, and a 30 nm intrinsic i-GaN layer was grown at the same temperature with an unintentional doping concentration of less than 1 × 10⁻⁶. 16 cm -3 Finally, silane (SiH4) was introduced as an n-type dopant source to grow a 30 nm n-GaN layer with a silicon doping concentration of approximately 5 × 10⁻⁶. 16 cm -3 Ultimately, an epitaxial layered structure is formed. S2: Gate Region Etching: First, photoresist is spin-coated onto the wafer surface, including the area forming the epitaxial stack, and the area outside the active region pattern is exposed by photolithography; then, inductively coupled plasma (ICP) dry etching is used, employing a gas (flow rate ratio of 2:1:2) Cl2 / BCl3 / Ar mixed gas, at an etching power of 500W and a gas pressure of 3mTorr, precisely etching from the n-GaN layer to the Al layer on both sides of the epitaxial stack. x Ga 1-x An N-barrier layer is formed to create a PIN gate structure; S3: Perform mesa isolation etching to define the active region; the specific process includes: First, photoresist is spin-coated onto the wafer surface, including the PIN gate structure, and the area outside the active region pattern is exposed by photolithography. Then, inductively coupled plasma (ICP) dry etching is used with a Cl2 / BCl3 / Ar mixed gas (flow rate ratio of 2:1:2) at an etching power of 500W and a gas pressure of 3mTorr to precisely etch away the semiconductor epitaxial layer (including barrier layer, channel layer, etc.) in the exposed area, down to the high-resistivity GaN buffer layer or substrate. After etching, the photoresist is removed and the wafer is cleaned, thereby forming physically isolated islands of active regions on the wafer, each composed of raised mesa.

[0024] S4: Using electron beam evaporation and rapid thermal annealing processes, source and drain ohmic contacts (Ti / Al / Ni / Au metal stack) are fabricated on the AlGaN barrier layers on both sides of the gate.

[0025] Specifically, it includes: 1) Electron beam evaporation deposition: Ti / Al / Ni / Au metal stacks are sequentially deposited on the AlGaN barrier layer in a high vacuum cavity; the thicknesses are 20 / 100 / 50 / 50 nm respectively.

[0026] 2) Stripping: Dissolve the photoresist with acetone to remove unwanted metal, leaving only the electrode pattern within the window.

[0027] 3) Rapid thermal annealing: The wafer is rapidly thermally treated at 800°C for 45 seconds in an N2 atmosphere to alloy the metal and semiconductor and form a low-resistance ohmic contact.

[0028] Example 2 In this embodiment, the working principle and band structure of the PIN-HEMT device prepared in Example 1 are analyzed. The core physical mechanism of the high performance of the device of the present invention originates from the modulation of the band structure by its unique PIN gate structure and its optimization effect in the photoelectric effect.

[0029] like Figure 2 As shown, this diagram illustrates the energy band structure of the PIN-HEMT gate region (n-GaN / i-GaN / p-GaN) and the underlying barrier and channel layers in Example 1. In the dark (solid black lines), the energy bands bend due to the built-in electric fields formed between p-GaN and i-GaN, n-GaN, and between p-GaN and the AlGaN barrier layer. At this time, the two-dimensional electron gas (2DEG) in the channel is fully depleted, the device is normally off, and the source-drain current is extremely small.

[0030] When ultraviolet light irradiates the device (as shown in the image) Figure 2 (As shown by the light blue dashed line) Photons with energies greater than the band gap of GaN and AlGaN materials are absorbed, exciting a large number of electron-hole pairs throughout the PIN region and barrier layer. Figure 3 (Illustration of paired black and white dots). Under the influence of the built-in electric field, photogenerated holes (…). Figure 3 The white dots in the middle are swept toward the p-GaN layer and accumulate, while photogenerated electrons ( Figure 3 The black dots in the middle are then swept toward the n-GaN layer and the AlGaN / GaN heterojunction interface below.

[0031] Photogenerated holes accumulated near the p-GaN layer significantly modulate the energy band at the interface between the p-GaN and AlGaN barrier layers (e.g., Figure 2 As shown by the bandgap change under illumination, this effectively reduces the depletion effect on the 2DEG in the channel, resulting in a sharp increase in channel conductivity and a significant rise in source-drain current. This process is similar to applying a positive gate voltage, but is entirely generated by the photogenerated carrier effect, thus achieving extremely high photoelectric gain. Figure 3 The description further illustrates that in the complete device, after ultraviolet light incidence, electrons are transported from the AlGaN barrier layer and GaN channel layer to the 2DEG channel, the 2DEG channel is turned on, the device's conductivity is restored, and holes accumulate in the p-GaN region. Figure 2 The modulation mechanism clearly demonstrates the transport path of electrons and holes.

[0032] Example 3 In this embodiment, the performance of PIN-HEMT as the core photosensitive element of an ultraviolet photodetector is verified through experiments.

[0033] The PIN-HEMT prepared in Example 1 was tested. The source and drain of the device were connected to the test circuit, and the gate was left floating to optimize performance. A wavelength-tunable ultraviolet LED was used as the light source to illuminate the channel region of the device.

[0034] like Figure 4 As shown, the output characteristic curve of the device under dark conditions exhibits an extremely low drain current density. Within the tested drain voltage range (0-3V), the dark current density remains at 10. -8 The extremely low levels below mA / mm indicate the device's excellent off-state characteristics and low noise level. When the device is irradiated with ultraviolet light of a specific wavelength, its output characteristic curve changes significantly, with the photocurrent density increasing by several orders of magnitude. Calculations show that the device's photo-dark current on / off ratio (Ion / Ioff) is greater than 10 throughout the test bias range. 9 This performance indicator far exceeds that of conventional photodetectors, directly demonstrating that the present invention, by introducing a PIN gate structure, greatly optimizes the control efficiency of photogenerated carriers in the bandgap design, thereby achieving extremely high optical signal detection sensitivity.

[0035] The table below shows the results at a drain bias of 1V and a flow rate of 10μW / cm. 2 Under the condition of incident optical power (Iopt), PIN-HEMT devices and P-GaN-HEMT devices (such as Figure 5 (As shown) Photoresponsivity at different ultraviolet wavelengths (300nm, 317nm, 335nm, 354nm); where the gate length of both PIN-HEMT and P-GaN-HEMT devices is 1μm, the gate width is 50μm, and the total active area is 500μm. 2 Test data shows that this PIN-HEMT-based device exhibits extremely high photoresponsivity across the stated wavelength range. Specific responsivity values ​​are shown in Table 1 below. Table 1. Responsivity of PIN-HEMT and P-GaN at different optical wavelengths As shown in Table 1, the PIN-HEMT structure device described in this invention, as a photosensitive element of an ultraviolet photodetector, exhibits a photoresponsivity that is more than eight orders of magnitude higher than that of the traditional p-GaN gate structure. This superior performance, combined with... Figure 5 The demonstrated ultra-high on / off ratio collectively confirms that by introducing a PIN gate structure, this invention achieves comprehensive optimization of the generation, separation, and control processes of photogenerated carriers at the bandgap level, thereby obtaining unprecedented photoelectric detection performance.

[0036] In summary, the PIN-HEMT structure provided by this invention not only possesses excellent normally-off transistor characteristics, but also exhibits ultra-low dark current (~10) in ultraviolet photodetector applications. -8 mA / mm, ultra-high switching ratio (>10) 9 ) and ultra-high responsiveness (~10) 7 Its significant advantage (on a scale of several orders of magnitude) makes it extremely promising for applications in fields such as solar-blind ultraviolet detection, low-light imaging, high-speed optical communication, and high-sensitivity sensing.

[0037] This invention optimizes the generation, separation, and gate control processes of photogenerated carriers from the perspective of band structure by introducing a PIN gate structure without significantly increasing the complexity of the process. This simultaneously improves the threshold voltage and reliability of AlGaN / GaNHEMT devices, as well as the photoresponsivity of the photosensitive element as an ultraviolet photodetector. It has important application value in fields such as solar-blind ultraviolet detection, imaging, and optical communication.

[0038] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An AlGaN / GaN transistor with a PIN gate structure, characterized in that, It includes, from bottom to top in sequence: a substrate, a GaN buffer layer, a GaN channel layer, and an Al x Ga 1-x GaN barrier layer, where 0 < x < 1; It is characterized in that the transistor further includes a P-I-N gate structure located on the Al x Ga 1-x GaN barrier layer, and a source electrode and a drain electrode respectively disposed on the Al x Ga 1-x GaN barrier layer and on both sides of the P-I-N gate structure; The PIN gate structure comprises, from bottom to top, a p-type GaN layer, an intrinsic i-GaN layer, and an n-type GaN layer.

2. An AlGaN / GaN transistor with a PIN gate structure according to claim 1, characterized in that, The Al x Ga 1-x In the N-barrier layer, x is 0.2 and the thickness is 25 nm.

3. An AlGaN / GaN transistor with a PIN gate structure according to claim 1, characterized in that, The thickness of the GaN channel layer is 200 nm.

4. An AlGaN / GaN transistor with a PIN gate structure according to claim 1, characterized in that, In the PIN gate structure: the thickness of the p-type GaN layer is 100 nm, and the Mg doping concentration is 1 × 10⁻⁶. 18 cm -3 The intrinsic i-GaN layer has a thickness of 30 nm and is an undoped layer; the n-type GaN layer has a thickness of 30 nm and a Si doping concentration of 5 × 10⁻⁶. 16 cm -3 .

5. An AlGaN / GaN transistor with a PIN gate structure according to claim 1, characterized in that, The source and drain are formed in the Al x Ga 1-x Ti / Al / Ni / Au multilayer metal ohmic contact electrode on N-barrier layer.

6. A method for fabricating an AlGaN / GaN transistor with a PIN gate structure according to any one of claims 1-5, characterized in that, Includes the following steps: S1, GaN buffer layer, GaN channel layer and Al are epitaxially grown sequentially on the substrate. x Ga 1-x N-barrier layer; then in Al x Ga 1-x An epitaxial stacked structure is formed by sequentially growing a p-type GaN layer, an intrinsic i-GaN layer, and an n-type GaN layer on an N-barrier layer. S2, at both sides of the epitaxial stacked structure, is etched from the n-type GaN layer down to Al using inductively coupled plasma dry etching. x Ga 1-x An N-barrier layer is formed to create the PIN gate structure; S3, perform mesa isolation etching on the epitaxial stacked structure containing the PIN gate structure to define the active region of the transistor; S5, the source and drain are fabricated on the AlxGa1-xN barrier layers located on both sides of the PIN gate structure.

7. The method for fabricating an AlGaN / GaN transistor with a PIN gate structure according to claim 6, characterized in that, When fabricating the source and drain electrodes, electron beam evaporation is used to deposit the source and drain metals, and thermal annealing is performed to form ohmic contacts.

8. An ultraviolet photodetector, characterized in that, Includes the AlGaN / GaN transistor with a PIN gate structure as described in any one of claims 1-5.

9. An ultraviolet photodetector according to claim 8, characterized in that, The source and drain of the transistor are configured as the photoelectric signal output terminals of the ultraviolet photodetector; the channel of the transistor and the structure located in the Al x Ga 1-x The region above the N-barrier layer is configured as a photosensitive region for receiving incident ultraviolet light.

10. The application of the AlGaN / GaN transistor with a PIN gate structure according to any one of claims 1-5 in solar-blind ultraviolet band detection and imaging.

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