Non-polar surface gan-based terahertz quantum cascade laser and its active region structure

Abstract

The application discloses an active region structure of a non-polar plane GaN-based terahertz quantum cascade laser, characterized in that the active region has multiple periods of three-well structure, wherein the potential well layer is GaN and the potential barrier layer is AlGaN; and a corresponding non-polar plane GaN-based terahertz quantum cascade laser. An active region structure of a two-well structure and a laser are also disclosed. The application discloses two active region structures of a three-well resonant phonon and a two-well phonon scattering injection terahertz quantum cascade laser based on a non-polar plane GaN, when the doping is 6*10 10 cm ‑2 , the peak gain of the two structures at 10K is 90.1 and 91.3 cm ‑1 , respectively, at 300K, the peak gain of 41.8 and 44.2 cm ‑ 1 is obtained at 8.2 and 7.7 terahertz, which is higher than the calculated double-metal waveguide loss. The overall results show that at room temperature, a GaN-based terahertz quantum cascade laser is possible at about 8 terahertz.

Description

Technical Field

[0001] This invention relates to a nonpolar GaN-based terahertz quantum cascade laser and its active region structure, belonging to the field of semiconductor device technology. Background Technology

[0002] Terahertz (THz) quantum cascade lasers have attracted widespread attention due to their extensive applications in spectroscopy, chemical detection, imaging, and medical astronomy. Operating temperature has long been a core issue limiting the use of terahertz quantum cascade lasers in laboratory environments, due to the necessity of cryogenic cooling. Extensive research has been conducted in this area, and recently, a double-well terahertz quantum well based on a resonant phonon (RP) scheme has achieved a significant operating temperature of 250 K. This can be fabricated into a compact and portable terahertz quantum well system integrated with a thermoelectric cooler. GaAs / AlGaAs terahertz quantum cascade lasers are severely limited in the frequency gap of solid-state coherent sources (5.5-12 THz), mainly because the polaron bandgap of GaAs material is approximately 30-50 meV, and nonradiative transitions achieved via longitudinal optical (LO) phonons are much faster than radiative transitions. To overcome this limitation, GaN is considered a potential candidate device because its LO phonon energy (~90 meV) is much higher than that of GaAs (~36 meV), which helps suppress thermal backfill and reduces deactivation of the upper lasing level (ULL) through thermally activated LO phonon emission. For these reasons, GaN / AlGaN terahertz quantum cascade lasers are considered potential devices that simultaneously satisfy the gap frequency and improve the operating temperature.

[0003] Due to the significant lattice / thermal mismatch between GaN / AlGaN and the substrate, the growth of GaN / AlGaN systems is less mature than that of GaAs and InP. The extremely strong polarization field of 0.1–1 MV / cm results in a zigzag-shaped conduction band profile in polar GaN (c-plane), meaning the top of the quantum barrier and the bottom of the quantum well form a triangle. This makes design and simulation more complex than with traditional composite semiconductor systems. Since the alignment of sub-band states is crucial for both injection and extraction processes, accurate determination of sub-band state energies is essential. However, the polarization charge at the interface of the GaN / AlGaN heterostructure introduces significant uncertainty into the band distribution. This is due to the difficulty in accurately quantifying the polarization charge density. These are determined by spontaneous polarization and piezoelectric polarization, which are directly related to the AlN mole fraction in the AlGaN barrier and the residual strain in the active layer. Furthermore, the errors in spontaneous polarization and piezoelectric coefficients in the group III nitride system remain substantial, not to mention the band distortion caused by the interface roughness of the polarization charge distribution profile. Therefore, GaN-based terahertz quantum cascade lasers are extremely challenging. Summary of the Invention

[0004] The purpose of this invention is to provide an active region structure for a nonpolar GaN-based terahertz quantum cascade laser.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An active region structure for a nonpolar GaN-based terahertz quantum cascade laser, characterized in that the laser structure employs a nonpolar (m-plane) GaN / AlGaN multi-quantum-well structure as the active region layer.

[0007] Preferably, the active region contains a period of multiple three-well structures, characterized by a well / barrier / well / barrier / well / barrier structure, wherein the well layer is GaN and the barrier layer is AlGaN. The thickness of the three-well structure corresponds to... The barrier layer is Al. 0.15 Ga 0.85 N.

[0008] Preferably, in each triple well, the widest potential well layer contains doping with a doping concentration of 2–16 × 10⁻⁶. 10 cm -2 The width of the doped region is 2–5 nm.

[0009] Preferably, the number of cycles is 100 or more.

[0010] Preferably, the active region contains a period of multiple two-well structures, characterized by a well / barrier / well / barrier structure, wherein the well layer is GaN and the barrier layer is AlGaN. The thickness of the two-well structure corresponds to... The barrier layer is Al. 0.2 Ga 0.8 N.

[0011] Preferably, in each dual-well, the widest potential well layer contains doping with a doping concentration of 2–16 × 10⁻⁶. 10 cm -2 The width of the doped region is 2–5 nm.

[0012] Preferably, the number of cycles is 100 or more.

[0013] The present invention also discloses a nonpolar GaN-based terahertz quantum cascade laser, comprising the above-described active region structure.

[0014] This invention discloses two active region structures for terahertz quantum cascade lasers based on nonpolar GaN (m-plane) triple-well resonant phonon (RP) and two-well phonon scattering injection (PSI) terahertz lasers, when the doping is 6 × 10⁻⁶. 10 cm -2At 10K, the peak gains of the two structures are 90.1 and 91.3 cm⁻¹, respectively. -1 The peak gains at 300K remained at 41.8 and 44.2 cm, respectively. -1 At 300K, 41.8 and 44.2 cm⁻¹ were obtained at 8.2 and 7.7 terahertz, respectively. -1 The peak gain is higher than the calculated bimetallic waveguide loss (31cm). -1 The overall results demonstrate that GaN-based terahertz quantum cascade lasers can achieve lasing at around 8 terahertz frequencies at room temperature. Gain spectra show that lasing occurs at 8.2 and 7.7 THz, both exceeding those of conventional GaAs terahertz quantum cascade lasers, enabling unprecedented terahertz-frequency lasing at room temperature using GaN-based terahertz quantum cascade lasers. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a triple-well resonant phonon (RP) quantum cascade laser structure.

[0016] Figure 2 This is the energy band diagram of two adjacent cycles in the active region of a triple-well resonant phonon mode (RP) quantum cascade laser. The operating bias is 135 mV / cycle at 10 kΩ. Tight-bound (TB) mode is used at the injection barrier between adjacent cycles. The potential well (GaN) and barrier (Al) for each cycle are shown. 0.15 Ga 0.85 The thickness of N) is (The underlined value indicates the barrier thickness). The doping density of the periodic plate is set to 6 × 10⁻⁶. 10 cm -2 It is doped throughout the widest well.

[0017] Figure 3 For RP, (a) is the maximum optical gain, (b) is the applied bias voltage and current density, and (c) is the photon energy and gain spectrum.

[0018] Figure 4 A schematic diagram of a two-well phonon scattering injection (PSI) quantum cascade laser structure.

[0019] Figure 5 The energy band diagrams for three adjacent cycles of a two-well phonon scattering injection (PSI) terahertz quantum cascade laser are shown. The operating bias is 155 mV / cycle at 10 kΩ. Tight-bound (TB) mode is used at the injection barrier between adjacent cycles. The potential well (GaN) and the barrier (Al) are also shown. 0.2 Ga 0.8 N) The thickness of each cycle is (The underlined value indicates the barrier thickness). The periodic plate doping density is set to 6 × 10⁻⁶. 10 cm-2 It is doped throughout the widest well.

[0020] Figure 6 (a) Maximum optical gain, (b) applied bias voltage and current density, and (c) photon energy as a function of gain spectrum, calculated from 10 to 300 K for two-well phonon scattering injection (PSI) design.

[0021] Figure 7 This is a schematic diagram of the three-dimensional structure of a nonpolar GaN-based terahertz quantum cascade laser, which, from bottom to top, includes a substrate, a metal waveguide, a doped layer, an active region, another doped layer, and a metal waveguide. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] An active region structure for a nonpolar GaN-based terahertz quantum cascade laser, comprising multiple periods of nonpolar Al 0.15 Ga 0.85 N is used as the potential barrier, and nonpolar GaN is used as the well. The layer sequence (in angstroms) within one period is: 22.3 / 33.2 / 10 / 24.3 / 20 / 58.2, forming a three-well resonant phonon structure. The widest well contains doping, with a doping density of 6 × 10⁻⁶. 10 cm -2 The region is 5nm wide, such as Figure 2 As shown, the polarization charge density at the heterojunction of the active region is zero. The resulting laser emits light at a frequency of 8.2 THz.

[0025] In this active region structure of the triple-well resonant phonon (RP), charge carriers tunnel from the injection level (IL4'') of the previous cycle to the upper laser level (ULL 1) via resonant tunneling. Radiative transitions occur from the upper laser level (ULL 1) to the lower laser level (LLL 2), emitting photons. Subsequently, the pump level (EL 3) pumps the charge carriers from the lower laser level (LLL 2) and relaxes them to the injection level (IL 4) at an extremely high speed through LO phonon scattering in the phonon trap (the widest trap), before being injected into the next cycle.

[0026] Radiative transitions occur between the upper laser level (ULL 1) and the lower laser level (LLL 2), with the oscillator intensity (f)... 21 )Depend on Given, among which It is the effective mass of electrons, v 21 It is the radiation frequency, z 21 These are the dipole matrix elements of ULL 1 and LLL 2. According to... Where ΔN 21 Let f be the three-dimensional doping density, c be the speed of light in a vacuum, n be the effective exponent of the model of interest, Δv be the linewidth of the radiative transition, and ε0 be the dielectric index. 21 Set it to a fairly large value to achieve a high gain.

[0027] The carrier distribution, current density, and gain characteristics of a GaN / AlGaN terahertz quantum cascade laser considering broadening effects were analyzed using the nonequilibrium Green's function. Both elastic scattering (charged impurities, interface roughness, and alloy disorder) and inelastic scattering (optical and acoustic phonons) were considered. The Poisson and Schrödinger equations were solved self-consistently using NextNano software to calculate the nonequilibrium Green's function, ultimately yielding the maximum optical gain, applied bias voltage and current density, and photon energy as a function of gain for this active region structure. Figure 3 As shown.

[0028] Example 2

[0029] A nonpolar GaN-based terahertz quantum cascade laser, the structure of which is as follows: Figure 1 and Figure 7 As shown, from bottom to top, it includes a substrate, a metal waveguide, a doped layer, an active region, another doped layer, and a metal waveguide, wherein the structure of the active region is the same as that in Example 1.

[0030] Example 3

[0031] An active region structure for a nonpolar GaN-based terahertz quantum cascade laser, comprising multiple periods of nonpolar Al 0.2 Ga 0.8 N is used as the potential barrier, and nonpolar GaN is used as the well. The layer sequence (in angstroms) within one period is: 24.2 / 52.6 / 10 / 32.8, forming a two-well phonon scattering injection structure. The widest well contains doping, with a doping density of 6 × 10⁻⁶. 10 cm -2 The region is 5nm wide, such as Figure 5 As shown, the polarization charge density at the heterojunction of the active region is zero. The resulting laser emits light at a frequency of 7.7 THz.

[0032] In this two-well phonon scattering injection (PSI) active region structure, a higher Al composition (20%) is used to provide stronger confinement. Charge carriers are injected into the extracted level (EL 1) through the injection barrier. The charge carriers are relaxed to the upper laser level (ULL 2) at an extremely fast speed through LO phonon scattering. Subsequently, a radiative transition occurs from the upper laser level (ULL 2) to the lower laser level (LLL 3), emitting photons. Finally, the charge carriers in the lower laser level achieve population inversion by being extracted to the next cycle's extracted level (EL 1').

[0033] The carrier distribution, current density, and gain characteristics of a GaN / AlGaN terahertz quantum cascade laser considering broadening effects were analyzed using the nonequilibrium Green's function. Both elastic scattering (charged impurities, interface roughness, and alloy disorder) and inelastic scattering (optical and acoustic phonons) were considered. The Poisson and Schrödinger equations were solved self-consistently using NextNano software to calculate the nonequilibrium Green's function, ultimately yielding the maximum optical gain, applied bias voltage and current density, and photon energy as a function of gain for this active region structure. Figure 6 As shown.

[0034] Example 4

[0035] A nonpolar GaN-based terahertz quantum cascade laser, the structure of which is as follows: Figure 4 and Figure 7 As shown, from bottom to top, it includes a substrate, a metal waveguide, a doped layer, an active region, another doped layer, and a metal waveguide, wherein the structure of the active region is the structure of Example 3.

[0036] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An active region structure for a nonpolar GaN-based terahertz quantum cascade laser, characterized in that... The laser structure employs a nonpolar GaN / AlGaN multi-quantum-well structure as the active region layer. The active region contains multiple periodic triple-well structures, characterized by a barrier / well / barrier / well / barrier / well pattern. The potential well layer is nonpolar GaN, and the barrier layer is nonpolar AlGaN. The thicknesses of the triple-well structures are 22.3 / 33.2 / 10 / 24.3 / 20 / 58.2 Å, respectively. The barrier layer is AlGaN. 0.15 Ga 0.85 N, the polarization charge density at the heterojunction of the active region is zero.

2. The active region structure of the nonpolar GaN-based terahertz quantum cascade laser according to claim 1, characterized in that: In each triple-well array, the widest potential well layer is doped with a doping concentration ranging from 2 to 16 × 10⁻⁶. 10 cm -2 The width of the doped region is 2~5nm.

3. The active region structure of the nonpolar GaN-based terahertz quantum cascade laser according to claim 2, characterized in that: The number of cycles is over 100.

4. An active region structure for a nonpolar GaN-based terahertz quantum cascade laser, characterized in that: The active region contains a periodicity of multiple two-well structures, characterized by a barrier / well / barrier / well pattern. The well layer is nonpolar GaN, and the barrier layer is nonpolar AlGaN. The thicknesses of the two-well structures are 24.2 / 52.6 / 10 / 32.8 Å, respectively. The barrier layer is AlGaN. 0.2 Ga 0.8 N, the polarization charge density at the heterojunction of the active region is zero.

5. The active region structure of the nonpolar GaN-based terahertz quantum cascade laser according to claim 4, characterized in that: In each dual-well, the widest potential well layer contains doping with a doping concentration of 2–16 × 10⁻⁶. 10 cm -2 The width of the doped region is 2~5nm.

6. The active region structure of the nonpolar GaN-based terahertz quantum cascade laser according to claim 4 or 5, characterized in that: The number of cycles is over 100.

7. A nonpolar GaN-based terahertz quantum cascade laser, characterized in that... The active region structure includes any one of claims 1-6.

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