GaN-based heterostructure phononic crystal filter and preparation method thereof

Abstract

The application provides a GaN-based heterostructure phonon crystal filter and a preparation method thereof. The filter comprises a substrate, a first semiconductor layer, an active layer, a phonon crystal filter layer and a second semiconductor layer which are sequentially prepared on the substrate. The phonon crystal filter layer comprises a P-type AlGaN electron blocking layer, a first P-type GaN layer and a superlattice structure which are sequentially prepared on the active layer. The superlattice structure is formed by stacking AlN layers and GaN layers which are periodically arranged. The second semiconductor layer comprises a second P-type GaN layer and a transparent conductive layer which are sequentially prepared on the superlattice structure. The GaN-based heterostructure phonon crystal filter in the application embeds a periodic AlN / GaN film stack in an LED epitaxial structure, forms a Bragg reflection type phonon band gap by using the significant acoustic impedance difference between the two materials, and accurately controls the center frequency of the acoustic band gap through the period thickness of the superlattice.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a GaN-based heterostructure phononic crystal filter and its fabrication method. Background Technology

[0002] 5G RF front-ends primarily employ surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. SAW filters offer cost advantages but are limited in operating frequency (typically below 2.5 GHz); BAW filters can operate at higher frequencies but face challenges such as limited power capacity and insufficient temperature stability. Traditional BAW filters are mainly based on AlN piezoelectric materials and metal electrode structures, which differs significantly from the current mainstream GaN power device platform, making on-chip integration difficult.

[0003] Defects or shortcomings of existing technology: 1) LED epitaxial processes and BAW filter processes have been developed separately, lacking a unified material platform to achieve functional integration. Specifically, LED epitaxy is usually completed in MOCVD equipment based on GaN material system, while BAW filters are based on sputtering or CVD processes of AlN thin film. The two have significant differences in substrate selection, growth temperature, doping control, etc., making it difficult to achieve collaborative integration on the same platform. 2) Traditional BAW filters use AlN material, which has a low piezoelectric coefficient, limiting the electromechanical coupling coefficient and sensitivity of the device; 3) Existing filters require independent packaging and assembly processes, and cannot be monolithically integrated with GaN power devices and LED light sources. This results in large system-level packaging volume, high cost, and significant parasitic effects, which is not conducive to the miniaturization and high-frequency development of RF front-end modules. Summary of the Invention To address the shortcomings of existing technologies, the present invention aims to provide a GaN-based heterostructure phononic crystal filter, thereby resolving the technical problems mentioned in the background section.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution: A GaN-based heterostructure phononic crystal filter includes a substrate and a first semiconductor layer, an active layer, a phononic crystal filter layer, and a second semiconductor layer sequentially fabricated on the substrate. The phononic crystal filter layer includes a P-type AlGaN electron blocking layer, a first P-type GaN layer, and a superlattice structure sequentially fabricated on the active layer. The superlattice structure is composed of periodically stacked AlN and GaN layers. The second semiconductor layer includes a second P-type GaN layer and a transparent conductive layer sequentially fabricated on the superlattice structure.

[0005] According to one aspect of the above technical solution, the substrate is a sapphire Al2O3 substrate, and the thickness of the substrate is 500μm~650μm.

[0006] According to one aspect of the above technical solution, the first semiconductor layer includes an AlN nucleation layer, a GaN buffer layer and a silicon-doped N-type GaN layer sequentially prepared on the substrate. The thickness of the AlN nucleation layer is 20nm~25nm, the thickness of the GaN buffer layer is 1μm~2μm, and the thickness of the silicon-doped N-type GaN layer is 1.5μm~3μm.

[0007] According to one aspect of the above technical solution, the active layer is formed by stacking InGaN layers and GaN layers arranged in a periodic manner, the number of periods of the InGaN well layer and the GaN barrier layer is 8 to 10, and the In composition of the InGaN well layer is 15% to 25%.

[0008] According to one aspect of the above technical solution, the thickness of the P-type AlGaN electron blocking layer is 15nm~25nm, and the thickness of the first P-type GaN layer is 50nm~100nm.

[0009] According to one aspect of the above technical solution, the number of periods of the AlN layer and GaN layer in the superlattice structure is 10 to 30, the thickness of the AlN layer in each period is 30 nm to 80 nm, the thickness of the GaN layer is 50 nm to 120 nm, and the total thickness of the superlattice structure is 1 μm to 5 μm.

[0010] According to one aspect of the above technical solution, the thickness of the second P-type GaN layer is 30nm~50nm, and the thickness of the transparent conductive layer is 100nm~200nm.

[0011] This invention also provides a method for fabricating a GaN-based heterostructure phonon crystal filter, comprising the following steps: Provide a substrate; A first semiconductor layer, an active layer, a phononic crystal filter layer, and a second semiconductor layer are sequentially fabricated on the substrate. The phonon crystal filter layer includes a P-type AlGaN electron blocking layer, a first P-type GaN layer, and a superlattice structure sequentially fabricated on the active layer. The superlattice structure is composed of periodically stacked AlN and GaN layers. The second semiconductor layer includes a second P-type GaN layer and a transparent conductive layer sequentially fabricated on the superlattice structure.

[0012] According to one aspect of the above technical solution, the first semiconductor layer includes an AlN nucleation layer, a GaN buffer layer, and a silicon-doped N-type GaN layer sequentially formed on the substrate. The growth temperature for forming the AlN nucleation layer is 400℃~600℃, the growth temperature for forming the GaN buffer layer is 1000℃~1100℃, and the carrier concentration of the silicon-doped N-type GaN layer is 2×10⁻⁶. 19 cm - ³.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: By embedding periodic AlN / GaN thin film stacks in the LED epitaxial structure, the significant acoustic impedance difference between the two materials (GaN acoustic impedance is approximately 26.8 × 10⁻⁶) is utilized. 6 kg / (m²·s), AlN acoustic impedance is approximately 34.6 × 10⁻⁶ kg / (m²·s). 6 The band gap is formed by the thickness of the superlattice (kg / (m²·s)), which is a Bragg reflector type phonon band gap. The center frequency of the band gap can be precisely controlled by the periodic thickness of the superlattice, with a control range covering 2GHz-60GHz, basically covering the main frequency bands of 5G millimeter-wave communication.

[0014] The entire heterostructure of the filter LED can be completed in a single MOCVD growth process without the need for subsequent bonding or transfer processes. This in-situ integration scheme significantly simplifies the process flow and improves device yield and reliability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the GaN-based heterostructure phononic crystal filter in the first embodiment of the present invention; Figure 2 This is a flowchart illustrating the fabrication method of a GaN-based heterostructure phononic crystal filter according to the second embodiment of the present invention. Explanation of key component symbols:

[0016] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0017] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0018] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] Please see Figure 1 The image shows a GaN-based heterostructure phononic crystal filter according to a first embodiment of the present invention, comprising a substrate 10, and a first semiconductor layer, an active layer 50, a phononic crystal filter layer 60, and a second semiconductor layer sequentially fabricated on the substrate 10. The phononic crystal filter layer 60 includes a P-type AlGaN electron blocking layer 61, a first P-type GaN layer 62, and a superlattice structure sequentially fabricated on the active layer 50. The superlattice structure is formed by stacking periodically arranged AlN layers 63 and GaN layers 64. The second semiconductor layer includes a second P-type GaN layer 70 and a transparent conductive layer 80 sequentially fabricated on the superlattice structure.

[0021] Understandably, this invention utilizes the significant acoustic impedance difference between the two materials (GaN acoustic impedance is approximately 26.8 × 10⁻⁶) by embedding periodic AlN / GaN thin film stacks in the LED epitaxial structure. 6 kg / (m²·s), AlN acoustic impedance is approximately 34.6 × 10⁻⁶ kg / (m²·s). 6 The band gap is formed by the thickness of the superlattice (kg / (m²·s)), which is a Bragg reflector type phonon band gap. The center frequency of the band gap can be precisely controlled by the periodic thickness of the superlattice, with a control range covering 2GHz-60GHz, basically covering the main frequency bands of 5G millimeter-wave communication.

[0022] The entire heterostructure of the filter LED can be completed in a single MOCVD growth process without the need for subsequent bonding or transfer processes. This in-situ integration scheme significantly simplifies the process flow and improves device yield and reliability.

[0023] Furthermore, the substrate 10 is a sapphire Al2O3 substrate 10, and the thickness of the substrate 10 is 500μm~650μm; the first semiconductor layer includes an AlN nucleation layer 20, a GaN buffer layer 30 and a silicon-doped N-type GaN layer 40 sequentially formed on the substrate 10, wherein the thickness of the AlN nucleation layer 20 is 20nm~25nm, the thickness of the GaN buffer layer 30 is 1μm~2μm, and the thickness of the silicon-doped N-type GaN layer 40 is 1.5μm~3μm.

[0024] Understandably, sapphire substrates possess advantages such as good chemical stability, excellent light transmittance, and relatively low price, making them the most widely used substrate material for commercial GaN-based LEDs. The low-temperature AlN nucleation layer 20, grown at 400℃~600℃, is used to alleviate lattice mismatch between the substrate 10 and the epitaxial layer. The high-temperature GaN buffer layer 30, grown at 1000℃~1100℃, is used to form a high-quality GaN template. The carrier concentration of the silicon-doped N-type GaN layer 40 is 2×10⁻⁶. 19 cm - ³, to provide sufficient electron injection for the device.

[0025] Furthermore, the active layer 50 is formed by stacking InGaN well layers and GaN barrier layers arranged in a periodic manner. The number of periods of the InGaN well layers and GaN barrier layers is 8 to 10, and the In composition of the InGaN well layer is 15% to 25% (corresponding to the emission wavelength of 450-530nm).

[0026] Understandably, in multi-quantum-well structures, the InGaN well layer acts as a potential well, and the GaN barrier layer acts as a potential barrier. Together, they form an alternating bandgap modulation structure, confining electrons and holes within the well layer and significantly increasing the radiative recombination probability. The In content within the well layer directly affects the emission wavelength; a higher In content results in a narrower band gap and a redshift in the emission wavelength. However, the In incorporation efficiency is limited by the growth temperature; excessively high temperatures lead to InN decomposition. Therefore, growth at a low temperature of around 780℃ is necessary.

[0027] Furthermore, the thickness of the P-type AlGaN electron blocking layer 61 is 15nm~25nm, and the thickness of the first P-type GaN layer 62 is 50nm~100nm.

[0028] Understandably, the element in the p-type AlGaN electron blocking layer 61 is Al0. 15 Ga0. 85 N, corresponding to a conduction band level of approximately 300 meV, can effectively block high-energy electrons overflowing from the active layer, preventing electrons from leaking into the P-region and causing nonradiative recombination, thereby improving the internal quantum efficiency of the device.

[0029] Furthermore, the number of periods of AlN layer 63 and GaN layer 64 in the superlattice structure is 10 to 30, the thickness of AlN layer 63 in each period is 30 nm to 80 nm, the thickness of GaN layer 64 is 50 nm to 120 nm, and the total thickness of the superlattice structure is 1 μm to 5 μm.

[0030] Furthermore, the thickness of the second P-type GaN layer 70 is 30nm~50nm, and the thickness of the transparent conductive layer 80 is 100nm~200nm.

[0031] Understandably, the second p-type GaN layer 70 is used as an ohmic contact buffer layer to reduce the contact barrier with the transparent conductive layer and obtain good ohmic contact characteristics. The transparent conductive layer uses indium tin oxide (ITO) or a Ni / Au composite transparent electrode, where ITO has high transmittance (>92%) and low resistivity (sheet resistance of approximately 15 Ω / cm). 2 Its excellent performance can effectively achieve lateral current expansion and improve light emission uniformity.

[0032] Finally, an ITO transparent conductive layer 80 is fabricated on top of the second P-type GaN layer 70, and P-type ohmic electrodes and N-type ohmic electrodes (consistent with existing technology, not shown in the figure) are prepared. The P-type ohmic electrode is a Ni / Au multilayer metal structure with a total thickness of 100nm~200nm, and the N-type ohmic electrode is a Ti / Al / Ti / Au multilayer metal structure with a total thickness of 150nm~300nm.

[0033] It should be noted that the superlattice structure in the phononic crystal filter layer 60 is the core innovation of this invention. Its working principle is based on phononic crystal theory. When sound waves propagate in the periodic elastic constant modulation structure, a phononic bandgap similar to the photonic bandgap in a photonic crystal is generated. Sound waves within the bandgap frequency range cannot pass through this structure and are completely reflected. AlN and GaN materials have a significant difference in acoustic impedance. This impedance discontinuity forms a highly efficient Bragg reflector in the periodic stack, enabling wide-bandwidth, high-reflectivity sound wave reflection characteristics.

[0034] Meanwhile, the structural parameters of the superlattice structure directly affect the filtering performance: Bragg condition: f = v / (2d); where f is the center frequency, v is the speed of sound, and d is the superlattice period thickness; for GaN material, the longitudinal speed of sound is approximately 7.9 km / s; for AlN material, the longitudinal speed of sound is approximately 10.9 km / s. This invention, by adjusting the superlattice period thickness d, can precisely set the center frequency of the filter to the desired frequency point. For example, to design a filter with a center frequency of 28 GHz, the period thickness d must satisfy: d=v / (2f) =7.9km / s / (2×28GHz)≈141nm, which allows for the design of a periodic structure with an AlN layer of 60nm and a GaN layer of 81nm.

[0035] The period number N and duty cycle r (AlN layer thickness / period thickness) of the phononic crystal are two other key parameters. The period number N determines the depth and steepness of the acoustic bandgap; the larger N is, the deeper the bandgap and the steeper the edge. N ≥ 20 is recommended. The duty cycle r affects the center frequency and bandwidth of the bandgap. The widest acoustic bandgap can be obtained when r ≈ 0.4~0.6.

[0036] Fabricating the filter within the LED epitaxial structure offers the following advantages compared to fabricating the LED structure or the filter separately: 1. The lattice mismatch between AlN and GaN is approximately 2.4%, resulting in extremely high stress accumulation in a superlattice spanning tens of periods. Direct growth on sapphire or Si substrates often requires thick buffer or gradient layers to release stress; otherwise, penetrating cracks are highly likely. In this design, the superlattice structure is grown on a complete LED epitaxial stack (including a GaN buffer layer, a silicon-doped N-type GaN layer, and an MQW active layer). These underlying structures act as a pre-strained engineering substrate. The underlying N-type semiconductor layer has already undergone stress relaxation with the sapphire substrate and exhibits a specific residual stress state. This residual stress can be transferred to the superlattice structure through the first part of the P-type GaN layer, allowing the superlattice structure to... The initial stress state of the superlattice shifts, resulting in an actual net stress lower than the theoretically calculated value. Simultaneously, the alternating compressive stress layers (AlN) and tensile stress layers (GaN) within the superlattice generate a periodic stress modulation field. When this stress field propagates downwards to the MQW active layer, it alters the quantum confinement Stark effect within the MQW. Consequently, by appropriately controlling the periodic thickness and duty cycle of the superlattice structure, the resulting stress field can partially offset the polarization electric field generated in the MQW active layer due to the InGaN / GaN lattice mismatch, thereby improving the internal quantum efficiency (IQE) of the LED. This cannot be achieved in a standalone LED or a standalone filter. A standalone filter structure lacks the MQW active layer as a beneficiary, and a standalone LED structure lacks the superlattice as a stress modulator.

[0037] 2. The interfaces of a standalone superlattice filter are typically air / electrode / substrate. Acoustic waves are easily reflected at these interfaces, forming standing waves or stray resonance modes, leading to increased insertion loss and worsened out-of-band suppression. The bandgap depth (i.e., acoustic suppression ratio) of a Bragg reflector phononic crystal depends on the number of periods N and the interlayer acoustic impedance ratio. To achieve a suppression ratio of -20dB or higher, N ≥ 30 or even more is often required, increasing the epitaxial thickness and fabrication complexity. In this scheme, the superlattice is sandwiched between two layers of p-GaN (the lower layer is the first part of p-GaN, and the upper layer is the second part of p-GaN), forming a fully embedded acoustic cavity structure. The more complex stacked layers below (P-type GaN layer, MQW active layer, and N-type GaN layer) constitute a gradient acoustic impedance matching network. The acoustic impedance from the sapphire substrate to the superlattice is a gradual transition rather than an abrupt change. This gradient matching effectively suppresses the back reflection of sound waves at the bottom of the superlattice, allowing more sound wave energy to be confined within the superlattice for Bragg scattering, which effectively increases the effective depth of the phonon bandgap. With the same number of cycles, the bandgap suppression depth of the LED-embedded superlattice structure is significantly improved compared to a standalone air interface filter. This means that the same or even better filtering performance can be achieved with fewer cycles and a thinner total thickness.

[0038] In summary, the GaN-based heterostructure phonon crystal filter in the above embodiments of the present invention utilizes the significant acoustic impedance difference between the two materials (GaN acoustic impedance is approximately 26.8 × 10⁻⁶) by embedding periodic AlN / GaN thin film stacks in the LED epitaxial structure. 6 kg / (m²·s), AlN acoustic impedance is approximately 34.6 × 10⁻⁶ kg / (m²·s). 6 The phonon bandgap is formed by the thickness of the superlattice structure (kg / (m²·s)). The center frequency of the phonon bandgap can be precisely controlled by the periodic thickness of the superlattice structure, with a control range covering 2-60 GHz, basically covering the main frequency bands of 5G millimeter-wave communication.

[0039] The entire heterostructure of the filter LED can be completed in a single MOCVD growth process without the need for subsequent bonding or transfer processes. This in-situ integration scheme significantly simplifies the process flow and improves device yield and reliability.

[0040] Please see Figure 2 The second embodiment of the present invention provides a method for fabricating a GaN-based heterostructure phonon crystal filter, comprising the following steps: S10 provides a substrate; For example, a patterned sapphire substrate with a thickness of 630 μm is selected as the substrate. The surface of the patterned substrate has a periodic microstructure, which can effectively scatter the light emitted from the active region, improve the light extraction efficiency of the LED, and also help improve the crystal quality of the epitaxial layer. S20, a first semiconductor layer, an active layer, a phonon crystal filter layer, and a second semiconductor layer are sequentially fabricated on the substrate.

[0041] The specific steps of step S20 include: A patterned sapphire substrate is placed in a PVD sputtering apparatus to deposit an AlN nucleation layer at a low temperature with a thickness of 20nm~25nm. PVD sputtering can obtain a uniform AlN film at a lower temperature, avoiding damage to the substrate surface caused by high temperature. After the AlN nucleation layer is deposited, the source sheet is placed in the MOCVD reaction chamber and annealed and recrystallized at 1100℃ in an NH3 atmosphere (3 minutes) to ripen the AlN nanoislands into preferentially oriented crystal nuclei, and then GaN buffer layer is grown. Please refer to the table below for the parameter settings of the MOCVD reaction chamber:

[0042] The GaN buffer layer undergoes a typical transition from three-dimensional island growth to two-dimensional layer growth. The in-situ reflectivity curve shows oscillating decay in the initial stage (3D nucleation), and then the reflectivity recovers and stabilizes (2D growth), indicating that the surface gradually flattens. Next, by setting the parameters of the MOCVD reaction chamber in the table below, the silicon-doped N-type GaN layer is grown;

[0043] Si doping achieves n-type conductivity by incorporating SiH4 into Ga sites. Under the aforementioned conditions, the Si doping efficiency is approximately 80%, and the actual carrier concentration is close to the Si atomic concentration. Hall measurements show an electron mobility of approximately 250 cm² / (V·s) and a resistivity of approximately 1.2 × 10⁻⁶. - ³ Ω·cm.

[0044] Next, the active layer is grown, which consists of periodically stacked InGaN well layers and GaN barrier layers. Growth requires lowering the temperature to promote In incorporation and switching to N2 carrier gas to avoid H2 etching of InN. The parameters of the MOCVD reaction chamber for growing the InGaN well layer and GaN barrier layer are shown in the table below: InGaN well layer:

[0045] GaN barrier layer:

[0046] In this embodiment, nine cycles of GaN barrier layers / InGaN well layers are grown alternately. After the InGaN well layer is grown at low temperature, NH3+N2 is introduced before the GaN barrier layer is grown to perform 2-second surface stabilization to prevent In desorption. The total thickness of the active multi-quantum well is approximately 92 nm.

[0047] Next, the P-type AlGaN electron blocking layer was grown, and the parameters of the MOCVD reaction chamber are shown in the table below:

[0048] The Al composition is controlled by adjusting the gas phase ratio of TMAl / (TMGa+TMAl). The Al composition of the p-type AlGaN electron blocking layer is 15%, with a conduction band level of about 300meV, which is sufficient to effectively block electron leakage. Mg doping requires subsequent thermal annealing for activation. Next, the first p-type GaN layer is grown, serving as the electron spreading layer. The parameters of its MOCVD reaction chamber are shown in the table below:

[0049] The next step is the growth of the superlattice structure, which requires the highest precision in the process. The superlattice structure is composed of periodically stacked AlN and GaN layers, and the thickness of each period needs to be controlled at the nanometer level, with a thickness deviation of less than 2nm per layer. Taking a 28GHz center frequency filter (period thickness d=141nm, AlN layer 60nm + GaN layer 81nm, number of periods N=25) as an example: The parameters of the MOCVD reaction chamber for preparing AlN layers (per layer) are shown in the table below:

[0050] The parameters of the MOCVD reaction chamber for preparing GaN layers (per layer) are shown in the table below:

[0051] In this embodiment, 25 alternating AlN / GaN layers are grown, resulting in a superlattice structure with a total thickness of approximately 3.525 μm. The growth rate is calibrated in real-time using in-situ optical reflectivity monitoring, and reflectivity oscillation period analysis is performed every 5 cycles. If necessary, the TMGa / TMAl flow rate is fine-tuned to maintain accurate repeatability of the cycle thickness. The steepness of the superlattice interface is ensured by a 2-second pure NH3 purification step after AlN growth and a 1-second H2 purification step after GaN growth, preventing interdiffusion of Al and Ga at the interface.

[0052] Key process points: Superlattice growth is carried out directly in situ on the first P-type GaN current-extended layer without the need for vacuum breaking or buffer transition layers. The high-temperature growth of the AlN layer at 1050°C ensures the high crystallinity quality of the layer, while the low-pressure growth at 100 Torr suppresses the gas phase pre-reaction, ensuring precise control of the AlN thickness.

[0053] Next, the second p-type GaN layer (ohmic contact buffer layer) is grown, and the parameters of its MOCVD reaction chamber are shown in the table below:

[0054] After the second p-type GaN layer is grown by MOCVD, cooling and Mg activation are performed: After epitaxial growth, the layer is annealed in an NH3 atmosphere for 20 minutes to activate the Mg acceptor in situ (driving out H from the Mg-H complex), then the NH3 atmosphere is turned off, and the layer is naturally cooled to room temperature in an N2 atmosphere before being removed. This in-situ activation process can achieve a hole activation rate of 5–10% for the second p-type GaN layer.

[0055] Finally, the chip manufacturing process is carried out: Mesa etching: Inductively coupled plasma (ICP) etching was used with the following parameters: Cl2 / BCl3 mixed gas (Cl2, 30 sccm; BCl3, 10 sccm), ICP power 500 W, RF bias power 100 W, and etching rate approximately 200 nm / min. Etching continued until the silicon-doped N-type GaN layer was exposed, forming an N-type electrode mesa with a depth of approximately 4.2 μm (penetrating the superlattice structure, the first P-type GaN layer, the P-type AlGaN electron blocking layer, and the active layer). Transparent conductive layer: ITO was deposited by magnetron sputtering with a target material of In₂O₃:SnO₂ = 90:10wt%, a sputtering power of 100W (RF), an Ar atmosphere pressure of 3mTorr, a deposition rate of approximately 5nm / min, and a target thickness of 150nm. After deposition, it was annealed in an RTA furnace at 550°C in an N₂ atmosphere for 1 minute, reducing the sheet resistance to approximately 15Ω / cm. 2 Visible light transmittance >92%.

[0056] The GaN-based heterostructure phonon crystal filter in the first embodiment can be fabricated using the above-described preparation method.

[0057] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," 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, the 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.

[0058] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A GaN-based heterostructure phonon crystal filter, characterized in that, The device includes a substrate and a first semiconductor layer, an active layer, a phonon crystal filter layer, and a second semiconductor layer sequentially formed on the substrate. The phonon crystal filter layer includes a P-type AlGaN electron blocking layer, a first P-type GaN layer, and a superlattice structure sequentially formed on the active layer. The superlattice structure is composed of periodically stacked AlN and GaN layers. The second semiconductor layer includes a second P-type GaN layer and a transparent conductive layer sequentially formed on the superlattice structure.

2. The GaN-based heterostructure phononic crystal filter according to claim 1, characterized in that, The substrate is a sapphire Al2O3 substrate with a thickness of 500μm~650μm.

3. The GaN-based heterostructure phonon crystal filter according to claim 1, characterized in that, The first semiconductor layer includes an AlN nucleation layer, a GaN buffer layer and a silicon-doped N-type GaN layer sequentially formed on the substrate. The thickness of the AlN nucleation layer is 20 nm to 25 nm, the thickness of the GaN buffer layer is 1 μm to 2 μm, and the thickness of the silicon-doped N-type GaN layer is 1.5 μm to 3 μm.

4. The GaN-based heterostructure phononic crystal filter according to claim 1, characterized in that, The active layer is composed of InGaN well layers and GaN barrier layers arranged in a periodic manner, with the number of periods of the InGaN well layers and GaN barrier layers being 8 to 10, and the In composition of the InGaN well layer being 15% to 25%.

5. The GaN-based heterostructure phononic crystal filter according to claim 1, characterized in that, The thickness of the P-type AlGaN electron blocking layer is 15nm~25nm, and the thickness of the first P-type GaN layer is 50nm~100nm.

6. The GaN-based heterostructure phononic crystal filter according to claim 1, characterized in that, The superlattice structure has 10 to 30 periods of AlN and GaN layers. In each period, the thickness of the AlN layer is 30 nm to 80 nm and the thickness of the GaN layer is 50 nm to 120 nm. The total thickness of the superlattice structure is 1 μm to 5 μm. In one period, the ratio of the thickness of the AlN layer to the thickness of the entire period is 0.4 to 0.

6.

7. The GaN-based heterostructure phononic crystal filter according to claim 1, characterized in that, The thickness of the second P-type GaN layer is 30nm~50nm, and the thickness of the transparent conductive layer is 100nm~200nm.

8. A method for fabricating a GaN-based heterostructure phonon crystal filter, characterized in that, Includes the following steps: Provide a substrate; A first semiconductor layer, an active layer, a phononic crystal filter layer, and a second semiconductor layer are sequentially fabricated on the substrate. The phonon crystal filter layer includes a P-type AlGaN electron blocking layer, a first P-type GaN layer, and a superlattice structure sequentially fabricated on the active layer. The superlattice structure is composed of periodically stacked AlN and GaN layers. The second semiconductor layer includes a second P-type GaN layer and a transparent conductive layer sequentially fabricated on the superlattice structure.

9. The method for fabricating a GaN-based heterostructure phonon crystal filter according to claim 8, characterized in that, The first semiconductor layer comprises an AlN nucleation layer, a GaN buffer layer, and a silicon-doped N-type GaN layer sequentially formed on the substrate. The growth temperature for forming the AlN nucleation layer is 400℃~600℃, the growth temperature for forming the GaN buffer layer is 1000℃~1100℃, and the carrier concentration of the silicon-doped N-type GaN layer is 2×10⁻⁶. 19 cm - ³.

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