MSM type full-gaN ultraviolet polarization detector and preparation method thereof

Abstract

The application belongs to the technical field of semiconductor device manufacturing, and particularly relates to a MSM type full GaN ultraviolet polarization detector and a preparation method thereof. The MSM type full GaN ultraviolet polarization detector comprises, from bottom to top, a substrate layer, an AlN buffer layer, a GaN layer and a metal electrode layer; the GaN layer comprises a GaN active layer and a nano-grating structure arranged on the surface of the GaN active layer; the metal electrode layer is composed of interdigital electrodes arranged in a symmetric interdigital shape; and the nano-grating structure is located between adjacent interdigital electrodes. The application etches GaN between the interdigital electrodes of a conventional MSM type GaN ultraviolet detector to form a periodic sub-wavelength GaN nano-grating structure, introduces geometric anisotropy on the surface of the device, makes the device produce significant absorption and response difference to ultraviolet light with different polarization directions, and the polarization ratio at 365 nm is 1.2, so that the polarization direction and polarization degree of the ultraviolet light can be accurately identified.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device manufacturing technology, specifically relating to an MSM-type all-GaN ultraviolet polarization detector and its fabrication method. Background Technology

[0002] Polarization, as a fundamental vector characteristic of light, carries additional information beyond intensity and wavelength, playing a crucial role in modern information technology. Polarization photodetector, a novel photoelectric detection technology, expands the information dimension of the target by sensing its polarization, enabling the extraction and resolution of the target's optical information. Therefore, developing high-performance polarization-sensitive ultraviolet detectors is key to driving technological breakthroughs in this field. Traditional polarization-sensitive ultraviolet detectors rely on discrete optical components such as external polarizers, waveplates, and filters, significantly increasing the complexity of the polarization detection system and hindering the miniaturization and integration of on-chip photoelectric systems. Consequently, developing monolithically integrated ultraviolet detectors with high polarization sensitivity and no need for external polarizers has become an urgent need in photoelectric detection. From an application perspective, due to their anisotropic response to polarized light, polarization-sensitive ultraviolet detectors have irreplaceable application value in polarization imaging, deep space exploration, communication encryption, and missile early warning.

[0003] GaN, as a typical third-generation wide-bandgap semiconductor material, has become an ideal material for developing high-performance ultraviolet photodetectors due to its advantages such as high thermal stability, high electron mobility, high breakdown electric field, excellent chemical stability, and radiation resistance. However, although traditional GaN-based ultraviolet detectors (such as MSM and PIN types) exhibit excellent sensitivity, they are only sensitive to light intensity and lack intrinsic polarization resolution, making it impossible to directly identify the polarization state of incident light. Therefore, they often require additional polarization components, resulting in a large system size that is difficult to integrate.

[0004] In recent years, polarization detectors have primarily employed low-dimensional semiconductor materials with anisotropic structures, such as one-dimensional nanomaterials, two-dimensional layered materials, and some semiconductor materials with intrinsic polarization responses. However, most low-dimensional semiconductors, due to their relatively narrow band gaps and instability under harsh environmental conditions, are mainly concentrated in the visible and infrared bands and cannot perform ultraviolet detection, limiting their practical application prospects. Meanwhile, heterostructures integrating 2D materials with GaN can achieve ultraviolet polarization detection, but the precise synthesis of low-dimensional materials and lattice mismatch between different material systems pose significant challenges. Furthermore, the optical anisotropy of semi-polar and non-polar AlGaN materials can be used to fabricate polarization detectors without polarizers and complex ultraviolet filters, but their growth process is difficult and the crystal quality of the material is hard to guarantee, resulting in numerous defects. In addition, metal nanogratings excite plasmonic resonance through interaction with incident ultraviolet light and utilize the strong polarization dependence of the resonance to achieve polarization selection. This method improves the light absorption efficiency and photocurrent of semiconductors through near-field light enhancement and optical trapping effects. While the aforementioned methods can improve light capture by extending the light propagation path, they also introduce additional optical losses, such as metallic absorption and refraction losses. Furthermore, the metal nanogratings suffer from metal-semiconductor heterojunctions and long-term instabilities in metallic materials, and the band limitations of plasmon resonance restrict the further development of polarization detectors. Therefore, developing anisotropic ultraviolet polarization wide-bandgap semiconductors and structures has become a significant challenge. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of existing technologies by providing an MSM-type all-GaN ultraviolet polarization detector based on an interdigitated electrode etched nanograting structure. By performing ICP etching on the GaN layer surface, a periodic subwavelength nanograting structure is formed between the interdigitated metal electrodes, creating structural anisotropy and thus realizing an all-GaN ultraviolet polarization detector. Compared to other methods, this simplifies the process and significantly improves stability. Semiconductor GaN nanogratings enhance light-matter interaction, strengthen the local light field and light absorption, amplify photon-carrier interaction, and effectively increase the light-receiving surface area, thereby significantly improving the device's photoresponse while effectively suppressing dark current. Furthermore, the periodic grating introduced by etching endows the device with strong geometric anisotropy. Based on the relative relationship between the polarization direction of the incident light and the grating line direction, the light absorption efficiency is highly dependent on the polarization direction of the incident light. As a result, the device exhibits significant differentiated responses to ultraviolet light with different polarization states, thus realizing monolithic integrated ultraviolet polarization detection without external polarization components. Moreover, it generates photocurrent without bias voltage, realizing self-driven detection and expanding the function of photodetectors.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] The first aspect of this invention provides an MSM-type all-GaN ultraviolet polarization detector, which comprises, from bottom to top, a substrate layer, an AlN buffer layer, a GaN layer, and a metal electrode layer; wherein, the GaN layer includes a GaN active layer and a nanograting structure disposed on the surface of the GaN active layer; the metal electrode layer is composed of interdigitated electrodes arranged in a symmetrical interdigitated shape; and the nanograting structure is located between adjacent interdigitated electrodes.

[0008] The metal electrode layer forms a Schottky contact with the GaN active layer.

[0009] The nanograting structure has a depth of 50-70 nm, a grating length of 100 nm, a grating width of 84-104 nm, a spacing between adjacent gratings of 96-116 nm, a grating structure period of 200 nm, and 40 grating periods between adjacent interdigitated electrodes.

[0010] In some embodiments of the present invention, the depth of the nanograting structure is 60 nm, the grating length is 100 nm, the grating width is 94 nm, the spacing between adjacent gratings is 106 nm, the grating structure period is 200 nm, and the number of grating periods between adjacent interdigitated electrodes is 40.

[0011] The interdigitated electrodes have an interdigitated finger width of 8-12 μm, an interdigitated finger length of 100 μm, and a spacing of 8-12 μm between adjacent interdigitated electrodes.

[0012] In some embodiments of the present invention, the interdigitated electrode has an interdigitated width of 10 μm, an interdigitated length of 100 μm, and a spacing of 10 μm between adjacent interdigitated electrodes.

[0013] The interdigitated electrode is a Ti / Au composite metal electrode; the Ti layer thickness in the Ti / Au composite metal electrode is 50 nm, and the Au layer thickness is 250 nm.

[0014] The substrate is a sapphire substrate, and its main component is Al2O3; the AlN buffer layer has a thickness of 50 nm; and the GaN active layer has a thickness of 1.8 μm.

[0015] A second aspect of this invention provides a method for fabricating an MSM-type all-GaN ultraviolet polarization detector, comprising the following steps:

[0016] Step 1: Deposit an AlN buffer layer on the substrate surface;

[0017] Step 2: Deposit a GaN layer on the AlN buffer layer;

[0018] Step 3: Deposit a symmetrical interdigitated metal electrode layer on the GaN layer to form a Schottky electrode;

[0019] Step 4: Perform photolithography and etching processes on the GaN layer between the symmetrical interdigitated electrodes to form the GaN active layer and the nanograting structure on its surface, thus obtaining the MSM-type all-GaN ultraviolet polarization detector.

[0020] In steps 1 and 2, the deposition process is metal-organic chemical vapor deposition.

[0021] In step 3, the deposition process is magnetron sputtering.

[0022] In step 4, the photolithography process is electron beam lithography; the etching process is inductively coupled plasma and BCl3 / Cl2 gas etching.

[0023] In some embodiments of the present invention, step 4 specifically includes the following steps: cleaning and drying the GaN epitaxial wafer with interdigitated electrodes; then spin-coating electron beam photoresist on the GaN layer surface and pre-baking it, and using electron beam lithography to expose and form a periodic nanograting pattern between adjacent interdigitated electrodes, wherein the grating structure period is 200 nm, the grating width is 94 nm, the spacing between adjacent gratings is 106 nm, and the number of grating periods between adjacent interdigitated electrodes is 40; after development, an etching mask corresponding to the preset grating structure is obtained to expose the GaN region to be etched; then, an inductively coupled plasma etching process is used to etch the exposed GaN layer with a BCl3 / Cl2 mixed gas to form a periodic subwavelength GaN nanograting structure with an etching depth of 60 nm on the surface of the GaN layer; after etching, the residual photoresist is removed and the wafer is cleaned and dried to finally form the GaN active layer and the nanograting structure on its surface.

[0024] The third aspect of this invention provides an application of an MSM-type all-GaN ultraviolet polarization detector in detecting polarized ultraviolet light.

[0025] In some embodiments of the present invention, the polarization-sensitive photocurrent of the MSM-type all-GaN ultraviolet polarization detector provided by the present invention and a conventional gratingless planar MSM detector are characterized. The results show that under 5V bias and 365nm illumination, the dichroic ratio of the MSM-type all-GaN ultraviolet polarization detector provided by the present invention is approximately 1.2, indicating sensitivity to polarized light; while the dichroic ratio of the conventional gratingless planar MSM detector is approximately 1, making it unable to identify polarized light information. This demonstrates the promising application prospects of the MSM-type all-GaN ultraviolet polarization detector in detecting polarized ultraviolet light.

[0026] Beneficial effects:

[0027] (1) The GaN nanograting structure of the present invention is an MSM ultraviolet polarization detector. GaN is etched between the interdigitated electrodes of a conventional MSM-type GaN ultraviolet detector to form a periodic subwavelength GaN nanograting structure. This introduces geometric anisotropy on the device surface, causing the device to produce significant differences in absorption and response to ultraviolet light with different polarization directions. The polarization ratio at 365 nm is 1.2, which can accurately identify the polarization direction and degree of polarization of ultraviolet light. The inherent geometric anisotropy realizes polarization-sensitive modulation without relying on external optical devices or phase tuning, thereby solving the problem of polarization detection that is difficult to achieve with conventional GaN-based MSM ultraviolet detectors and significantly expanding the function of photodetectors.

[0028] (2) The ultraviolet polarization detector of the present invention adopts an all-GaN structure. The GaN nanograting structure can enhance the interaction between light and matter, improve the ultraviolet light absorption efficiency, and increase the effective illumination area, thereby enhancing the local light field and photon-carrier interaction. At the same time, the nanograting enhances light absorption by reducing reflectivity and transmittance, thereby improving the generation and separation of carriers and significantly improving the device's optical response. In addition, the grating structure does not introduce additional heterogeneous interfaces, effectively avoiding surface leakage current caused by interface defects. While increasing photocurrent, it suppresses a significant increase in dark current, and the device has high signal-to-noise ratio and stability. Therefore, while possessing polarization detection capabilities, the device's optical response performance is also improved compared to the structure without a grating.

[0029] (3) The all-GaN ultraviolet polarization detector of the present invention requires only two core fabrication processes. By directly etching the surface of the GaN layer to form a nanograting, there is no need to introduce other heterogeneous materials or additional polarization components. This fundamentally avoids problems such as lattice mismatch and interface defects caused by complex epitaxial growth and heterogeneous integration processes, thereby making the device fabrication process simpler, the process controllability higher, and the device stability significantly improved. Attached Figure Description

[0030] The present invention will be further described in detail below with reference to the accompanying drawings, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0031] Figure 1 This is a schematic diagram of the structure of the MSM-type all-GaN ultraviolet polarization detector prepared in Example 1 of the present invention.

[0032] Figure 2 The above are the SEM characterization results of the GaN periodic subwavelength nanograting structure between the interdigitated electrodes prepared in Example 1 of this invention.

[0033] Figure 3The image shows the IV characteristic curves of the MSM-type all-GaN ultraviolet polarization detector prepared in Example 1 of this invention and the traditional MSM detector with a gratingless planar structure, respectively, under dark environment and 365nm monochromatic light illumination, as well as the spectral response curves of the polarization detector under different bias voltages.

[0034] Figure 4 The time response characteristics of the MSM-type all-GaN ultraviolet polarization detector prepared in Example 1 of this invention under 365nm illumination and a 2V bias voltage are shown.

[0035] Figure 5 Photocurrent diagrams of the MSM-type all-GaN ultraviolet polarization detector prepared in Example 1 of the present invention and the traditional MSM detector without grating planar structure under polarized light illumination at different polarization angles at 5V. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0037] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0038] Example 1:

[0039] This embodiment provides an MSM-type all-GaN ultraviolet polarization detector based on an interdigital nanograting structure of interdigital electrodes. Figure 1 This is a schematic diagram of the structure of an MSM-type all-GaN ultraviolet polarization detector, in which... Figure 1 In the diagram, 'a' represents the overall structure of the detector. Figure 1 In the diagram, b represents a schematic representation of the single-period cross-sectional structure of a nanograting. Figure 1 It can be seen that the MSM-type all-GaN ultraviolet polarization detector includes, from bottom to top: a sapphire substrate layer, an AlN buffer layer, a GaN layer, and a metal electrode layer; wherein, the GaN layer includes a GaN active layer and a nanograting structure on its surface; in the metal electrode layer, each metal electrode is arranged in a symmetrical interdigitated shape, and the GaN active layer between the interdigitated electrodes is etched to form the nanograting structure.

[0040] The sapphire substrate layer is 430 μm thick and mainly composed of Al2O3; the AlN buffer layer is 50 nm thick; the GaN active layer is 1.8 μm thick; the metal electrode layer has interdigitated metal electrodes symmetrically arranged on both sides, with an interdigitated width of 10 μm (±2 nm), an interdigitated length of 100 μm, and a spacing of 10 μm (±2 nm) between adjacent interdigitated electrodes. The interdigitated electrodes are made of Ti / Au composite metal, with a Ti layer thickness of 50 nm and an Au layer thickness of 250 nm.

[0041] Electron beam lithography was used to pattern the grating structure, and inductively coupled plasma and BCl3 / Cl2 gas were used to etch the GaN grating structure between the interdigital electrodes, resulting in a periodic subwavelength GaN nanograting structure with a depth of 60 nm, a length of 100 nm, a width of 94 nm (±10 nm), a spacing of 106 nm (±10 nm) between adjacent gratings, a period of 200 nm, and 40 grating periods between adjacent interdigital electrodes.

[0042] The aforementioned MSM-type all-GaN ultraviolet polarization detector is obtained by growing an epitaxial structure of the device on a sapphire substrate using metal-organic chemical vapor deposition (MOCVD), specifically including the following steps:

[0043] Step 1: Deposit an AlN buffer layer on the surface of a sapphire substrate using MOCVD;

[0044] Step 2: An unintentionally doped GaN layer of approximately 1.9 μm thickness was grown on the AlN buffer layer using MOCVD;

[0045] Step 3: After the GaN layer is grown, Ti / Au metal electrode layers with thicknesses of 50 nm and 250 nm are deposited on the GaN layer by magnetron sputtering. Schottky electrodes with symmetrical interdigitated shapes are prepared by standard photolithography and lift-off techniques.

[0046] Step 4: After fabricating the interdigitated electrodes, a nanograting structure is prepared on the GaN layer surface between the symmetrical interdigitated electrodes. First, the GaN epitaxial wafer with the interdigitated electrodes is cleaned and dried. Then, electron beam photoresist is spin-coated onto the GaN layer surface and pre-baked. Electron beam lithography is used to expose and form a periodic nanograting pattern between adjacent interdigitated electrodes. The grating structure has a period of 200 nm, a grating width of 94 nm, an adjacent grating spacing of 106 nm, and 40 grating periods between adjacent interdigitated electrodes. After development, an etching mask corresponding to the preset grating structure is obtained, exposing the GaN region to be etched. Then, inductively coupled plasma etching is used with a BCl3 / Cl2 mixed gas to etch the exposed GaN layer, forming an etching depth of 60 nm on the GaN layer surface. A periodic subwavelength GaN nanograting structure of nm was formed; after etching, the residual photoresist was removed and the surface was cleaned and dried to finally form the GaN active layer and its surface nanograting structure, thus obtaining the MSM-type all-GaN ultraviolet polarization detector.

[0047] Example 2:

[0048] To further illustrate the beneficial effects of the MSM-type all-GaN ultraviolet polarization detector based on the interdigital nanograting structure of interdigital electrodes provided in Example 1, a series of experiments were conducted.

[0049] Figure 2 The above are the SEM characterization results of the GaN periodic subwavelength nanograting structure between the interdigitated electrodes in Example 1. Figure 2 In the image, 'a' represents a low-magnification SEM image of the nanograting structure. Figure 2 In the image, b represents a high-magnification SEM image of the nanograting structure. Figure 2 As can be seen, the nanograting region prepared in Example 1 completely covers the interdigitated electrodes, with a complete structural morphology and clear boundaries. The grating lines are arranged in parallel along the same direction, with good line continuity. No obvious breaks, collapses or adhesions were observed, and the line width and spacing were consistent, exhibiting good periodicity and uniformity. This indicates that the prepared subwavelength periodic GaN nanograting has high quality.

[0050] Figure 3 The image shows the IV characteristic curves of the polarization detector prepared in Example 1 and the conventional gratingless planar MSM detector under dark conditions and 365 nm monochromatic illumination, as well as the spectral response curves of the polarization detector under different bias voltages. Figure 3 In this context, 'a' represents the IV characteristic curve. Figure 3 In the figure, b represents the spectral response curve. As can be seen from the IV curve, compared to the traditional GaN planar MSM ultraviolet detector, the introduction of the grating structure increases the device photocurrent and suppresses the increase in dark current. The dark current measured at room temperature is less than nA in the bias voltage range of -6V to 6V, and can be as low as 1.3 × 10⁻⁶ at a bias voltage of 4V. -12 A, the photocurrent at a bias voltage of 4 V is 6.7 × 10⁻⁶. -4 A. Therefore, the test results show that the polarization ultraviolet detector device provided in this application has a relatively ideal photocurrent-to-dark-current ratio, which is approximately 5.2 × 10⁻⁶. 8 .

[0051] The spectral response curves at different bias voltages between 0 and 10 V show that the cutoff wavelength of the polarization detector prepared in Example 1 is approximately 365 nm, consistent with the bandgap bandwidth of the GaN absorption layer. Furthermore, the responsivity increases with increasing applied bias voltage, reaching 145 A / W at 10 V, demonstrating the significant modulating effect of bias voltage on photoconductivity gain and carrier collection efficiency. Simultaneously, at 0 V, the polarization detector exhibits a clear cutoff at 365 nm, demonstrating self-driving characteristics and a responsivity of 0.05 A / W.

[0052] Figure 4The photocurrent transient response characteristics of the polarization detector prepared in Example 1 under 2V bias voltage and illumination by a 5.5Hz LED ultraviolet light signal with an emission wavelength of 365 nm were measured. The rise and fall times of the device can be defined as the time required for the photocurrent to rise from 10% to 90% of its final value. The measured rise and fall times of the device were 22 ms and 27 ms, respectively. The test results show that the polarization ultraviolet detector device provided in Example 1 has a relatively fast response speed.

[0053] Figure 5 The polarization-sensitive photocurrent as a function of polarization angle is shown in polarization coordinate plots of the polarization detector prepared in Example 1 and a conventional gratingless planar MSM detector under 5 V bias and 365 nm illumination. Figure 5 In the diagram, 'a' represents the photocurrent of a traditional gratingless planar MSM detector. Figure 5 In Figure 'b', the photocurrent diagram of the polarization detector prepared in Example 1 is shown. The comparison results clearly show that the dichroic color ratio of the nanograting structure polarization ultraviolet detector provided in Example 1 is approximately 1.2, indicating sensitivity to polarized light, while the dichroic color ratio of the planar MSM detector device is approximately 1, meaning it cannot identify polarized light information. The test results demonstrate that the polarization ultraviolet detector provided in this application possesses polarization detection capability sensitive to ultraviolet light.

[0054] In summary, the polarization ultraviolet detector of this invention can achieve self-driven polarization detection, low dark current, high sensitivity, fast response speed, and high responsivity. Therefore, this structural design overcomes the shortcomings of traditional ultraviolet detectors in recognizing polarized light information and significantly enhances photoresponse performance.

[0055] This invention provides an MSM-type all-GaN ultraviolet polarization detector and its fabrication method. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. An MSM-type all-GaN ultraviolet polarization detector, characterized in that, The MSM-type all-GaN ultraviolet polarization detector comprises, from bottom to top: a substrate layer, an AlN buffer layer, a GaN layer, and a metal electrode layer; wherein, the GaN layer includes a GaN active layer and a nano-grating structure disposed on the surface of the GaN active layer; the metal electrode layer is composed of interdigitated electrodes arranged in a symmetrical interdigitated shape; the nano-grating structure is located between adjacent interdigitated electrodes.

2. The MSM-type all-GaN ultraviolet polarization detector according to claim 1, characterized in that, The depth of the nanograting structure is 50~70 nm, the grating length is 100 nm, the grating width is 84~104 nm, the spacing between adjacent gratings is 96~116 nm, the grating structure period is 200 nm, and the number of grating periods between adjacent interdigital electrodes is 40.

3. The MSM-type all-GaN ultraviolet polarization detector according to claim 1 or 2, characterized in that, The interdigitated electrode has an interdigitated finger width of 8~12 μm, an interdigitated finger length of 100 μm, and a spacing of 8~12 μm between adjacent interdigitated electrodes.

4. The MSM-type all-GaN ultraviolet polarization detector according to claim 3, characterized in that, The interdigitated electrode is a Ti / Au composite metal electrode; the Ti layer thickness in the Ti / Au composite metal electrode is 50 nm and the Au layer thickness is 250 nm.

5. The MSM-type all-GaN ultraviolet polarization detector according to claim 1, characterized in that, The substrate is a sapphire substrate; the AlN buffer layer has a thickness of 50 nm; and the GaN active layer has a thickness of 1.8 μm.

6. The method for fabricating the MSM-type all-GaN ultraviolet polarization detector according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Deposit an AlN buffer layer on the substrate surface; Step 2: Deposit a GaN layer on the AlN buffer layer; Step 3: Deposit a symmetrical interdigitated metal electrode layer on the GaN layer to form a Schottky electrode; Step 4: Perform photolithography and etching processes on the GaN layer between the symmetrical interdigitated electrodes to form the GaN active layer and the nanograting structure on its surface, thus obtaining the MSM-type all-GaN ultraviolet polarization detector.

7. The preparation method according to claim 6, characterized in that, In steps 1 and 2, the deposition process is metal-organic chemical vapor deposition.

8. The preparation method according to claim 6, characterized in that, In step 3, the deposition process is magnetron sputtering technology.

9. The preparation method according to claim 6, characterized in that, In step 4, the photolithography process is electron beam lithography; the etching process is inductively coupled plasma etching.

10. The application of the MSM-type all-GaN ultraviolet polarization detector according to any one of claims 1 to 5 in detecting polarized ultraviolet light.

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