Gallium nitride quantum cascade laser based on silicon waveguide structure and preparation method thereof

Abstract

The application belongs to the technical field of semiconductor lasers, and particularly relates to a gallium nitride quantum cascade laser based on a silicon-based waveguide structure and a preparation method thereof. The application breaks through the technical prejudice that a silicon substrate is not suitable for a GaN-based THz-QCL, innovatively adopts high-resistance silicon as a substrate, and through systematic regulation and control of the doping concentration and thickness of a high-doped GaN plasma layer, a multi-period quantum cascade active region layer and a low-doped GaN contact layer, a new single-metal waveguide structure is constructed. Experimental and simulation results show that the structure realizes the comprehensive performance of an optical field confinement factor of 0.1-0.8 and waveguide loss of 10-150 cm ‑1 in the 7-10 THz frequency band; especially in the 8.5-10 THz high frequency band, the optical field confinement factor significantly surpasses the device based on a SiC substrate in the cited patent, and the loss is always controlled within 150 cm ‑1 The following is within a reasonable range that can realize net gain.

Description

Technical Field

[0001] This application belongs to the field of semiconductor laser technology, specifically relating to a gallium nitride quantum cascade laser based on a silicon-based waveguide structure. Background Technology

[0002] Terahertz quantum cascade lasers (THz-QCLs) are core coherent light sources in medical imaging, security detection, and spectral analysis. Breakthroughs in their performance are crucial for the development of cutting-edge technologies. Since the advent of THz-QCLs, traditional gallium arsenide (GaAs)-based systems have become the mainstream in research and development. However, this system is constrained by the inherent properties of the material. Strong absorption in the residual radiation band exists in the 7–9 THz range, and longitudinal optical (LO) phonons easily induce rapid non-radiative scattering, resulting in a significant terahertz gap in the critical 5–12 THz frequency band. This gap has become a fundamental technological bottleneck restricting the development of terahertz coherent light sources.

[0003] To overcome this bottleneck, researchers have shifted their focus to wide-bandgap semiconductor materials. Gallium nitride (GaN), with its ultra-high LO phonon energy of approximately 90 meV and a high-frequency residual beam band of 17–22 THz, can effectively circumvent the aforementioned defects of GaAs-based systems at the material level, making it an ideal candidate material for breaking through the 5–12 THz terahertz gap. This provides a novel solution for achieving effective lasing in this frequency band, and GaN-based THz-QCLs have thus become a core research and development direction in the field of terahertz light sources. In the development process of GaN-based THz-QCLs, after overcoming the frequency bottleneck at the material level, waveguide structure design quickly became the core issue restricting the actual performance of the devices. Currently, the mainstream waveguide structures for terahertz lasers are mainly divided into two categories: bimetallic waveguides (MM) and semi-insulating surface plasmon waveguides (SISP, single-metal waveguides). Bimetallic waveguides have a light field confinement factor close to 1, exhibiting excellent light field confinement. However, this structure requires complex wafer bonding and metal stripping processes, and the metal layer is extremely prone to breakage during fabrication, resulting in very low device yield and failing to meet the demands of large-scale production. Semi-insulating surface plasmon waveguides, on the other hand, are fully compatible with existing microelectronic processes, with a simple and easy fabrication process, making them the preferred solution for the industrialization of GaN-based THz-QCLs. However, their light field easily penetrates into the substrate region due to wavelength characteristics. The optical properties of the substrate in the terahertz band directly determine the waveguide's light field confinement capability and propagation loss. Furthermore, the lattice matching degree between the substrate and GaN affects the quality of the epitaxial material, thus indirectly limiting the device's electrical performance and reliability. Therefore, substrate selection and waveguide structure parameter design are the core research and development challenges for achieving low-loss, high-efficiency laser output in the 5–12 THz frequency band for GaN-based THz-QCLs.

[0004] For example, patent application number 202411521076.9 proposes a single-metal waveguide GaN-based terahertz quantum cascade laser. This laser uses GaN, AlN, or SiC as a substrate, and sequentially grows a highly doped layer, an active region, a lightly doped layer, and an electrode layer on the substrate. Performance tests show that, under specific film layer doping designs, through synergistic optimization of the substrate and each functional layer, the device can achieve an optical field confinement factor of 0.3 to 0.5 and a waveguide loss of 10 to 80 cm⁻¹ in the 5–12 THz frequency band. -1 It has the potential to achieve lasing in this frequency band, successfully covering a frequency range that is difficult for traditional GaAs-based systems to reach, demonstrating the feasibility of developing high-efficiency terahertz laser output.

[0005] However, GaN, AlN, and SiC are all strongly polar crystals, exhibiting significant lattice dispersion and optical phonon resonance absorption in the 7–10 THz frequency band, leading to a dramatic change in their dielectric constant with frequency. This intrinsic physical characteristic fundamentally causes optical field modes to leak into the substrate region, making it difficult to further improve the optical field confinement factor. Simultaneously, the leaked optical field readily interacts with free carriers in the highly doped contact layer, exacerbating absorption losses and resulting in persistently high waveguide losses, thus limiting the device's output power and electro-optical conversion efficiency. Furthermore, the industry currently lacks systematic research on the substrate material optical response, interface coupling mechanism, and waveguide mode modulation of GaN-based THz-QCLs in the 7–10 THz frequency band. A waveguide structure design system with low loss and high optical field confinement factor adapted to this frequency band has not yet been established, becoming a key bottleneck for achieving high-performance lasing. Summary of the Invention

[0006] The purpose of this application is to provide a gallium nitride quantum cascade laser with a high optical field confinement factor and low loss in the 7~10THz frequency band, which is achieved through the following technical solution:

[0007] A gallium nitride quantum cascade laser based on a silicon-based waveguide structure, characterized by having the following components connected in sequence:

[0008] A high-resistivity silicon substrate with a resistivity greater than or equal to 10 kΩ·cm and a thickness of 80–100 μm; a highly doped GaN plasma layer with a thickness of 300–600 nm and a silicon doping concentration of 5.0 × 10⁻⁶. 18 ~3×10 19 cm -3 Multi-period quantum cascade active region layer, with a thickness of 3~10 μm and a silicon doping concentration of 3×10⁻⁶. 16 ~5×10 16 cm -3 The GaN contact layer has a thickness of 20-40 nm and a silicon doping concentration of 1×10⁻⁶. 18 ~2×1018 cm -3 The laser further includes a cathode in contact with the lightly doped GaN contact layer and an anode in contact with the heavily doped GaN plasma layer; and when the thickness of the multi-period quantum cascade active region layer is greater than 5 μm, the thickness of the heavily doped GaN plasma layer is greater than 500 nm and / or the silicon doping concentration is greater than 1 × 10⁻⁶. 19 cm -3 When the thickness of the multi-period quantum cascade active region layer is less than 5 μm, the thickness of the highly doped GaN plasma layer is less than 500 nm and / or the silicon doping concentration is less than 1 × 10⁻⁶. 19 cm -3 .

[0009] Preferably, the resistivity of the high-resistivity silicon substrate is 10 kΩ·cm and the thickness is 80 μm; the thickness of the highly doped GaN plasma layer is 300 nm and the silicon doping concentration is 3 × 10⁻⁶. 19 cm -3 The thickness of the multi-period quantum cascade active region is 10 μm, and the silicon doping concentration is 3 × 10⁻⁶. 16 cm -3 The thickness of the low-doped GaN contact layer is 20 nm, and the silicon doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the cathode and anode is 1 μm.

[0010] Preferably, the resistivity of the high-resistivity silicon substrate is 10 kΩ·cm and the thickness is 80 μm; the thickness of the highly doped GaN plasma layer is 300 nm and the silicon doping concentration is 5 × 10⁻⁶. 18 cm -3 The thickness of the multi-period quantum cascade active region is 3 μm, and the silicon doping concentration is 3 × 10⁻⁶. 16 cm -3 The thickness of the low-doped GaN contact layer is 20 nm, and the silicon doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the cathode and anode is 1 μm.

[0011] Preferably, the resistivity of the high-resistivity silicon substrate is 10 kΩ·cm and the thickness is 80 μm; the thickness of the highly doped GaN plasma layer is 600 nm and the silicon doping concentration is 3 × 10⁻⁶. 19 cm -3 The thickness of the multi-period quantum cascade active region is 10 μm, and the silicon doping concentration is 3 × 10⁻⁶. 16 cm -3 The thickness of the low-doped GaN contact layer is 20 nm, and the silicon doping concentration is 1 × 10⁻⁶. 18 cm -3The thickness of the cathode and anode is 1 μm.

[0012] Preferably, the multi-period quantum cascade active region is composed of three AlGaN barrier layers with an Al composition of 10-14% and three GaN well layers stacked sequentially, with the thicknesses of the structural sequence being 12-14 Å, 45-47 Å, 6-8 Å, 35-37 Å, 12-15 Å, and 70-77 Å, respectively. The widest well layer is n-type doped, including 157-520 periodic structures.

[0013] Preferably, both the cathode and anode are made of Au metal with a thickness of 1~2μm.

[0014] The fabrication method of the gallium nitride quantum cascade laser based on silicon waveguide structure described in any of the above-mentioned methods includes the following steps: providing a high-resistivity silicon substrate; and using metal-organic chemical vapor deposition or molecular beam epitaxy to sequentially epitaxially grow the following on the high-resistivity silicon substrate: a highly doped GaN plasma layer, a multi-period quantum cascade active region layer, and a low-doped GaN contact layer.

[0015] Preferably, the preparation method further includes: after photolithography of the wafer, depositing electrodes on the surfaces of the low-doped GaN contact layer and the high-doped GaN plasma layer using electron beam evaporation or magnetron sputtering technology.

[0016] Compared with the prior art, this application has the following beneficial effects:

[0017] Although GaN-based terahertz quantum cascade lasers offer significant advantages at high frequencies, conventional wisdom generally holds that the severe lattice mismatch (approximately 17%) and difference in thermal expansion coefficients between silicon and GaN substrates lead to high defect density in the epitaxial layer and enhanced free carrier scattering, resulting in significant energy loss and hindering effective optical field confinement and low-loss transmission. Therefore, existing technologies, such as those cited in the patents, typically employ homogeneous or near-lattice-matched substrates like GaN, AlN, or SiC to achieve optical field confinement factors of 0.3–0.5 and waveguide losses of 10–80 cm⁻¹ in the 5–12 THz frequency band. -1 Performance.

[0018] However, this application breaks through the prevailing technical bias in the field: the inherent perception that silicon substrates are unsuitable for GaN-based terahertz quantum cascade lasers. This application innovatively uses high-resistivity silicon directly as the substrate and constructs a novel single-metal waveguide structure by systematically and synergistically controlling the thickness and doping concentration of the highly doped GaN plasma layer, the multi-period quantum cascade active region layer, and the low-doped GaN contact layer. Furthermore, it should be noted that the applicant's in-depth research has revealed a strong coupling and synergistic relationship between the highly doped GaN plasma layer and the multi-period quantum cascade active region layer in multi-layered structures. These two elements not only significantly influence waveguide loss but also affect the laser's cutoff frequency (i.e., the minimum operating frequency). Specifically, the thinner the highly doped GaN plasma layer, the lower the waveguide loss, but the correspondingly higher the cutoff frequency; the higher the doping concentration, the higher the blue shift of the plasma frequency (i.e., the absorption peak frequency), affecting waveguide loss and optical field confinement factor. The greater the thickness of the multi-period quantum cascade active region layer, the lower the waveguide loss and the higher the optical field confinement factor, but it also shifts the cutoff frequency towards higher frequencies. Experimental and simulation results show that this structure achieves an optical field confinement factor of 0.1–0.8 and a waveguide loss of 10–150 cm⁻¹ in the 7–10 THz frequency band. -1 The overall performance is superior; especially in the 8.5~10THz high frequency range, the optical field confinement factor significantly surpasses that of the SiC substrate-based device in the cited patent, and the loss is consistently controlled within 150cm². -1 The following is within a reasonable range for achieving net gain.

[0019] Furthermore, to further verify the synergistic effect of the technical solution in this application, a control experiment was also conducted: using the same high-resistivity silicon substrate, but adjusting the doping or thickness parameters of other films, the results all showed a decrease in optical field confinement capability and a significant increase in loss, making it impossible to simultaneously achieve a high optical field confinement factor and low loss. This fully demonstrates that the technical effect achieved in this application is not a simple superposition of single parameter optimizations, but rather an unexpected performance breakthrough resulting from the synergistic effect between each film layer and the high-resistivity silicon substrate. It successfully solves the long-standing technical prejudice that silicon substrates are unusable in GaN-based THz lasers, providing a new feasible path for low-cost, large-area THz light sources. Attached Figure Description

[0020] The attached diagram will be briefly described below:

[0021] Figure 1 This is a schematic diagram of a gallium nitride quantum cascade laser based on a silicon-based waveguide structure.

[0022] Figure 2 The output characteristics of the laser in Example 1 of Performance Test 1 at a frequency of 8 THz are shown.

[0023] Figure 3The output characteristics of the laser in Example 1 of Performance Test 1 are shown at a frequency of 10 THz.

[0024] Figure 4 The waveguide loss curve of the laser in Example 1 in the 7~10THz frequency band is shown.

[0025] Figure 5 The curves showing the optical field confinement factor variation of the laser in Example 1 within the 7-10 THz frequency band are shown.

[0026] Figure 6 The curve showing the relationship between the laser confinement factor and the waveguide loss ratio as a function of frequency in Example 1 is shown.

[0027] Figure 7 Waveguide loss curves for a comparative laser in the 7-10 THz frequency band;

[0028] Figure 8 The curves showing the variation of the optical field confinement factor of a comparative laser in the 7-10 THz frequency band are shown.

[0029] Figure 9 The curves showing the ratio of laser confinement factor to waveguide loss as a function of frequency are comparative examples.

[0030] Figure 10 The figure shows a cross-sectional schematic diagram of the gallium nitride quantum cascade laser based on a silicon-based waveguide structure, with the following labels: 100, high-resistivity silicon substrate; 200, highly doped GaN plasma layer; 300, multi-period quantum cascade active region layer; 400, low-doped GaN contact layer; 500, cathode; 600, anode. Detailed Implementation

[0031] The present application will now be further described by way of specific embodiments. Those skilled in the art will be able to implement the present application based on these descriptions. Furthermore, the embodiments of the present application described below are generally only a part of the embodiments of the present application, and not all of the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort should fall within the scope of protection of the present application.

[0032] Example 1

[0033] This embodiment provides a gallium nitride quantum cascade laser based on a silicon-based waveguide structure. From bottom to top, it consists of a high-resistivity silicon substrate, a highly doped GaN plasma layer, a multi-period quantum cascade active region layer, and a lightly doped GaN contact layer. The parameters of each functional layer are optimally matched parameters, as detailed below:

[0034] High-resistivity silicon substrate: A high-resistivity silicon substrate with a resistivity of 10 kΩ·cm and a thickness of 80 μm is used;

[0035] Highly doped GaN plasma layer: 300 nm thick, silicon doping concentration 3.0 × 10⁻⁶ 19 cm -3 The material was epitaxially grown on a high-resistivity silicon substrate using metal-organic chemical vapor deposition (MOCVD) technology.

[0036] Multi-period quantum cascade active region: 10 μm thick, composed of three AlGaN barrier layers (12% Al composition) and three GaN well layers stacked sequentially. The thicknesses of the structural sequence are: 13.4 Å, 46.1 Å, 7.4 Å, 36 Å, 13 Å, and 74 Å. The widest well layer is n-type doped, with a sheet doping density of 3 × 10⁻⁶. 16 cm -3 It includes 400 periodic structures.

[0037] Low-doped GaN plasma layer: 20 nm thick, silicon doping concentration 1.0 × 10⁻⁶ 18 cm -3 The material is epitaxially grown on the surface of a multi-period quantum cascade active region layer using MOCVD technology.

[0038] Cathode and anode: Au metal, 1.0 μm thick.

[0039] The laser fabrication method described in this embodiment specifically includes the following steps:

[0040] Substrate pretreatment. Provided. <111> The semi-insulating high-resistivity silicon substrate was ultrasonically cleaned for 10 minutes each with acetone, anhydrous ethanol, and deionized water, and then dried with a nitrogen gun at a 45° angle.

[0041] Epitaxial growth of functional layers. The pretreated high-resistivity silicon substrate was placed in the MOCVD reaction chamber. First, high-purity H2 (99.9999% purity) was used as the carrier gas, and the substrate was thermally cleaned for 10 minutes at 1000℃ and 76 Torr. Then, high-purity H2 was maintained as the carrier gas (the flow rate was kept stable at 20 slm throughout the process). NH3 (99.9999% purity) was used as the N source, TMGa (99.9999% purity) as the Ga source, and SiH4 (99.9999% purity, diluted in H2, concentration 50 ppm) as the Si doping source. By precisely controlling the gas source flow rate, reaction temperature, and pressure, each functional layer was epitaxially grown sequentially. Before each layer growth, a 3-minute gas source purging was performed to ensure a uniform growth atmosphere. The growth parameters and in-situ annealing parameters for each layer are as follows:

[0042] Highly doped GaN contact layer. Growth temperature 1080℃, reaction chamber pressure 76 Torr (atmospheric pressure), TMGa flow rate 45 sccm, NH3 flow rate 2000 sccm (NH3 / TMGa molar ratio ≈ 1200), SiH4 flow rate 10 sccm, growth rate 1.5 nm / min. After growing to 500 nm, maintain temperature 1080℃ and pressure 76 Torr, stop SiH4 introduction, and continue to introduce NH3 and H2 for in-situ annealing for 8 min.

[0043] Multi-period quantum cascade active region layer. After annealing, the reaction temperature was reduced to 880℃ at a rate of 3℃ / min, the pressure was adjusted to 50 Torr, the TMGa flow rate was 25 sccm, the NH3 flow rate was 1500 sccm, the SiH4 flow rate was 0.3 sccm, and the growth rate was 0.6 nm / min (error ≤ ±0.05 nm). Eighty triple-barrier triple-well periodic structures were grown sequentially, and the total thickness was grown to 8 μm. Then, the temperature was maintained at 880℃ and the pressure at 50 Torr, and in-situ annealing was carried out with NH3 and H2 for 15 min.

[0044] Low-doped GaN waveguide layer. After annealing, the reaction temperature was restored to 1080℃ at a rate of 5℃ / min, the pressure was adjusted back to 76 Torr, the TMGa flow rate was 35 sccm, the NH3 flow rate was 1800 sccm, the SiH4 flow rate was 0.2 sccm, and the growth rate was 1.2 nm / min. After growing to 30 nm, the temperature was maintained at 1080℃ and the pressure at 76 Torr. The SiH4 flow was stopped, and NH3 and H2 were introduced for in-situ annealing for 8 min. After completion, the wafer was cooled to room temperature in the furnace at a rate of 3℃ / min and then removed.

[0045] Photolithography defines the patterned area. Spin-coating photoresist. Using positive photoresist (such as AZ6130, suitable for GaN wet / dry etching processes), spin-coat the wafer surface at 5000 r / min for 30 s. After spin-coating, place it on a hot plate and pre-bake at 90℃ for 90 s. The photoresist film thickness is precisely controlled to 1.0 μm.

[0046] Exposure and development. A UV lithography machine (wavelength 365nm) was used for proximity exposure (10μm gap) via a custom-designed mask, with an exposure dose of 180mJ / cm². 2 After exposure, the sample was placed in a 2.38% tetramethylammonium hydroxide (TMAH) developer and developed at 25°C for 60 seconds. Then, it was ultrasonically cleaned with deionized water for 1 minute (50W power) and dried with nitrogen to expose the top waveguide ridge (150μm wide and 3mm long) and the electrode pattern area (120μm wide and 3mm long).

[0047] Post-baking. After development, place on a hot plate and bake at 110°C for 60 minutes.

[0048] Depositing the cathode and anode. The photolithographically etched wafer is placed in an electron beam evaporation coating machine. First, the chamber is baked and degassed (150℃, 30 min), then the vacuum level is evacuated to 8×10⁻⁶. -5 Pa was used as the evaporation source with a high-purity Au target (purity 99.999%), an electron beam power of 120W, and a deposition rate precisely controlled at 0.3nm / s. Evaporation was stopped when the cathode and anode thickness reached 1.0μm. The wafer temperature was maintained at 25±2℃ throughout the process. After deposition, the wafer was kept in a vacuum chamber for 30min.

[0049] Post-processing and shaping.

[0050] Photoresist removal. Place the wafer with deposited cathode and anode in an acetone solution at 80°C and sonicate for 5 minutes (80W). Then replace with fresh acetone solution and soak for 10 minutes to remove residual photoresist and excess Au metal on the surface. Then rinse with anhydrous ethanol and deionized water for 5 minutes each, and dry with nitrogen.

[0051] Dry etching refinement. Inductively coupled plasma (ICP) dry etching technology was employed. Before etching, the wafer was treated with O2 plasma (300W, 1 min) to remove residual photoresist. Subsequently, a Cl2 / BCl3 mixed gas (volume ratio 2:1) was used as the etching gas, with a total gas flow rate of 40 sccm, etching power of 400W, bias power of 80W, chamber pressure of 0.8 Pa, and etching rate of 30 nm / min to refine the waveguide ridge region, etching to a waveguide ridge sidewall perpendicularity ≥89.5°. During etching, an optical probe was used to monitor the etching depth in real time to avoid over-etching. After etching, the wafer was ultrasonically cleaned with deionized water for 2 min (power 50W) and dried with nitrogen.

[0052] Annealing activation. Add a metal-semiconductor contact annealing step: Place the etched wafer in a rapid annealing furnace and anneal at 350°C for 10 minutes in a N2 atmosphere (99.999% purity), then cool to room temperature with the furnace;

[0053] Final cleaning. The device was placed in dilute hydrochloric acid (volume ratio 1:20) and immersed at 25°C for 3 minutes to remove residual metal chloride impurities from the etching process. Then, it was rinsed repeatedly with deionized water 3 times (5 minutes each time). Finally, it was dried with a nitrogen gun along the parallel direction of the device surface to obtain a gallium nitride quantum cascade laser device based on a silicon-based waveguide structure.

[0054] Example 2

[0055] This embodiment provides a gallium nitride quantum cascade laser based on a silicon-based waveguide structure. Its layered structure is consistent with that of Embodiment 1. The parameters of each functional layer are the lower limit adaptation parameters of the protection range, as detailed below:

[0056] High-resistivity silicon substrate: A high-resistivity silicon substrate with a resistivity of 10 kΩ·cm and a thickness of 80 μm is used;

[0057] Highly doped GaN plasma layer: 300 nm thick, silicon doping concentration 5.0 × 10⁻⁶ 18 cm -3 ;

[0058] Multi-period quantum cascade active region: 3 μm thick, silicon doping concentration 3.0 × 10⁻⁶ 16 cm -3 ;

[0059] Low-doped GaN contact layer: 20 nm thick, silicon doping concentration 1.0 × 10⁻⁶ 18 cm -3 ;

[0060] Cathode and anode: Au metal, 1 μm thick.

[0061] Example 3

[0062] This embodiment provides a gallium nitride quantum cascade laser based on a silicon-based waveguide structure. Its layered structure is consistent with that of Embodiment 1. The parameters of each functional layer are the lower limit adaptation parameters of the protection range, as detailed below:

[0063] High-resistivity silicon substrate: A high-resistivity silicon substrate with a resistivity of 10 kΩ·cm and a thickness of 80 μm is used;

[0064] Highly doped GaN plasma layer: 600 nm thick, silicon doping concentration 3 × 10⁻⁶ 19 cm -3 ;

[0065] Multi-period quantum cascade active region: 10 μm thick, silicon doping concentration 3 × 10⁻⁶ 16 cm -3 ;

[0066] Low-doped GaN contact layer: 20 nm thick, silicon doping concentration 1.0 × 10⁻⁶ 18 cm -3 ;

[0067] Cathode and anode: Au metal, 1 μm thick.

[0068] Comparative Example 1

[0069] This comparative example provides a gallium nitride quantum cascade laser based on a silicon-based waveguide structure. Its layered structure is consistent with that of Example 1. The parameters of each functional layer are the lower limit of the protection range adaptation parameters, as follows:

[0070] High-resistivity silicon substrate: A high-resistivity silicon substrate with a resistivity of 10 kΩ·cm and a thickness of 80 μm is used;

[0071] Highly doped GaN plasma layer: 300 nm thick, silicon doping concentration 5.0 × 10⁻⁶ 18 cm -3 ;

[0072] Multi-period quantum cascade active region: 10 μm thick, silicon doping concentration 3.0 × 10⁻⁶ 16 cm -3 ;

[0073] Low-doped GaN contact layer: 20 nm thick, silicon doping concentration 1.0 × 10⁻⁶ 18 cm -3 ;

[0074] Cathode and anode: Au metal, 1 μm thick.

[0075] Performance Test 1

[0076] This performance test focuses on the gallium nitride quantum cascade laser based on a silicon-based waveguide structure prepared in Example 1. One-dimensional optical field distribution simulation analysis was performed using Matlab software to obtain the optical field intensity distribution cloud map of the device (e.g., ...). Figure 2 , 3 (As shown).

[0077] Figure 2 The light field intensity distribution characteristics of the laser at a frequency of 8 THz are shown. The light field energy is highly concentrated in the multi-period quantum cascade active region and the adjacent GaN plasma layer regions. The light field peak appears precisely at the center of the active region. The light field attenuation rate towards the high-resistivity silicon substrate is gradual in the vertical direction. The light field intensity in the region beyond 12 μm on the substrate side has decreased exponentially from 0.8 au to the light field on the top side. The light field intensity in the region beyond 50 μm on the metal layer side is almost 0. There is no obvious light field mode leakage phenomenon. This proves that at a frequency of 8 THz, the silicon-based waveguide structure can achieve efficient confinement of the light field in the active region through the synergistic effect of the high-resistivity silicon substrate, plasma layer, etc., and the light field confinement effect is excellent. Figure 3 The light field intensity distribution characteristics of the laser at a frequency of 10 THz are highly consistent with those at 8 THz. The light field energy is still mainly concentrated in the multi-period quantum cascade active region layer, with no obvious light field shift or diffusion. Only the boundary of the light field peak region is more compact than that at 8 THz, and the attenuation trend towards the substrate and metal layer is further accelerated. Even at the high frequency of 10 THz, there is still no significant light field leakage on the high-resistivity silicon substrate side, and the confinement effect of the top on the light field is further enhanced. This fully demonstrates that the silicon-based waveguide structure of this application has stable and efficient light field confinement capability in the entire frequency band of 7~10 THz, which is suitable for the light field transmission requirements of the above frequency band and ensures the effective lasing of the laser in this frequency band from the structural level.

[0078] Performance Test 2

[0079] This performance test focuses on the gallium nitride quantum cascade lasers based on silicon-based waveguide structures prepared in Example 1 and the comparative example. The photoelectric performance in the 7–10 THz frequency band was measured under ambient temperature and pressure (25°C, 1 atm). The testing equipment employed a terahertz time-domain spectrometer (THz-TDS) coupled with a semiconductor laser characteristic testing system. Quantitative measurements of waveguide loss and optical field confinement factor across the entire 7–10 THz frequency band were performed. The test results are shown below. Figures 4-9 As shown.

[0080] See Figure 4 It can be observed that the waveguide loss of the device in the 7~10THz frequency band increases slowly and linearly with increasing frequency, and the waveguide loss at 7THz is approximately 10cm. -1 At 8THz, it is approximately 40cm. -1 At 9THz, it is approximately 90cm. -1 At 10THz, it is approximately 150cm. -1 The waveguide loss is less than 150cm across the entire frequency band. -1 This demonstrates the low-loss transmission advantages of silicon-based waveguide structures. (See also...) Figure 5 It can be observed that the optical field confinement factor of the device steadily increases with frequency. The optical field confinement factor is about 10% at 7THz, about 50% at 8THz, about 70% at 9THz, and reaches 80% at 10THz, which is a significant improvement compared to existing GaN-based single-metal waveguide lasers (20%~50%).

[0081] Further, see the comparative examples attached. Figure 7 It can be observed that the waveguide loss of the device in the 7~10THz frequency band increases linearly with increasing frequency, and the waveguide loss at 7THz is approximately 45cm. -1 At 8THz, it is approximately 125cm. -1 At 9THz, it is approximately 210cm. -1 At 10THz, it is approximately 200cm. -1 The waveguide losses across the entire frequency band are significantly higher than in Example 1, and the losses in the 9-10 THz high-frequency band far exceed the reasonable range for achieving net gain. This highlights that without the optimal parameter matching of this application, the lattice fit between the film layers in the silicon-based waveguide structure is poor, significantly exacerbating energy loss during optical transmission. (See also...) Figure 8It can be observed that the optical field confinement factor of the device increases with frequency. At 7 THz, the optical field confinement factor is approximately 20%, at 8 THz approximately 55%, at 9 THz approximately 70%, and at 10 THz it reaches 80%, which is comparable to Example 1 in the high-frequency range. However, considering the loss data, the comparative example sacrifices loss performance for some optical field confinement effect, while Example 1 achieves a dual optimization of low loss and high optical field confinement factor across the entire frequency range: at 7 THz, the loss of Example 1 is only 10 cm⁻¹. -1 It is far lower than the 45cm of the comparative figure. -1 Although the optical field confinement factor is 10%, the loss advantage is significant; in the 8~10THz frequency band, Example 1 maintains a steady increase in the optical field confinement factor while keeping the loss consistently at 150cm. -1 The following comparison of the sharp increase in loss after 8THz in the comparative example fully demonstrates that Example 1, through the precise synergistic design of parameters of various film layers such as silicon substrate, highly doped GaN plasma layer, and active region layer, achieves superior overall performance in optical field confinement and low-loss transmission, which is far better than the parameter combination scheme of the comparative example.

Claims

1. A gallium nitride quantum cascade laser based on a silicon-based waveguide structure, characterized in that, The following are connected in sequence: High-resistivity silicon substrate with a resistivity greater than or equal to 10 kΩ·cm and a thickness of 80~100 μm; A highly doped GaN plasma layer with a thickness of 300–600 nm and a silicon doping concentration of 5.0 × 10⁻⁶ nm. 18 ~3×10 19 cm -3 ; Multi-period quantum cascade active region layer, with a thickness of 3~10 μm and a silicon doping concentration of 3×10⁻⁶. 16 ~5×10 16 cm -3 ; The GaN contact layer has a thickness of 20-40 nm and a silicon doping concentration of 1×10⁻⁶. 18 ~2×10 18 cm -3 ; The laser also includes a cathode in contact with the low-doped GaN contact layer and an anode in contact with the high-doped GaN plasma layer; Furthermore, when the thickness of the multi-period quantum cascade active region layer is greater than 5 μm, the thickness of the highly doped GaN plasma layer is greater than 500 nm and / or the silicon doping concentration is greater than 1 × 10⁻⁶. 19 cm -3 When the thickness of the multi-period quantum cascade active region layer is less than 5 μm, the thickness of the highly doped GaN plasma layer is less than 500 nm and / or the silicon doping concentration is less than 1 × 10⁻⁶. 19 cm -3 .

2. The gallium nitride quantum cascade laser based on a silicon-based waveguide structure according to claim 1, characterized in that, The high-resistivity silicon substrate has a resistivity of 10 kΩ·cm and a thickness of 80 μm; the highly doped GaN plasma layer has a thickness of 300 nm and a silicon doping concentration of 3 × 10⁻⁶. 19 cm -3 The thickness of the multi-period quantum cascade active region is 10 μm, and the silicon doping concentration is 3 × 10⁻⁶. 16 cm -3 The thickness of the low-doped GaN contact layer is 20 nm, and the silicon doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the cathode and anode is 1 μm.

3. The gallium nitride quantum cascade laser based on a silicon-based waveguide structure according to claim 1, characterized in that, The high-resistivity silicon substrate has a resistivity of 10 kΩ·cm and a thickness of 80 μm; the highly doped GaN plasma layer has a thickness of 300 nm and a silicon doping concentration of 5 × 10⁻⁶. 18 cm -3 The thickness of the multi-period quantum cascade active region is 3 μm, and the silicon doping concentration is 3 × 10⁻⁶. 16 cm -3 The thickness of the low-doped GaN contact layer is 20 nm, and the silicon doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the cathode and anode is 1 μm.

4. The gallium nitride quantum cascade laser based on a silicon-based waveguide structure according to claim 1, characterized in that, The high-resistivity silicon substrate has a resistivity of 10 kΩ·cm and a thickness of 80 μm; the highly doped GaN plasma layer has a thickness of 600 nm and a silicon doping concentration of 3 × 10⁻⁶. 19 cm -3 The thickness of the multi-period quantum cascade active region is 10 μm, and the silicon doping concentration is 3 × 10⁻⁶. 16 cm -3 The thickness of the low-doped GaN contact layer is 20 nm, and the silicon doping concentration is 1 × 10⁻⁶. 18 cm -3 The thickness of the cathode and anode is 1 μm.

5. The gallium nitride quantum cascade laser based on a silicon-based waveguide structure according to any one of claims 1 to 4, characterized in that, The multi-period quantum cascade active region consists of three AlGaN barrier layers with an Al composition of 10-14% and three GaN well layers stacked sequentially. The thicknesses of the structural sequence are 12-14 Å, 45-47 Å, 6-8 Å, 35-37 Å, 12-15 Å, and 70-77 Å, respectively. The widest well layer is n-type doped, and includes 157-520 periodic structures.

6. The gallium nitride quantum cascade laser based on a silicon-based waveguide structure according to claim 1, characterized in that, Both the cathode and anode are made of Au metal with a thickness of 1~2μm.

7. The method for fabricating a gallium nitride quantum cascade laser based on a silicon-based waveguide structure as described in any one of claims 1 to 6, characterized in that, Includes the following steps: A high-resistivity silicon substrate is provided; using metal-organic chemical vapor deposition or molecular beam epitaxy, the following are epitaxially grown sequentially on the high-resistivity silicon substrate: a highly doped GaN plasma layer, a multi-period quantum cascade active region layer, and a low-doped GaN contact layer.

8. The method for fabricating a gallium nitride quantum cascade laser based on a silicon-based waveguide structure according to claim 7, characterized in that, The preparation method further includes: after photolithography on the wafer, electrodes are deposited on the surfaces of the low-doped GaN contact layer and the high-doped GaN plasma layer using electron beam evaporation or magnetron sputtering technology.

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