A quantum cascade laser with a novel band structure

Abstract

The present invention provides a quantum cascade laser with a novel energy band structure, comprising: an InP substrate, and an injection region and an active region prepared on the InP substrate. A deep potential well is nested within a shallow well in the active region, and a high potential barrier is nested within a high potential barrier in the injection region, thereby significantly reducing the leakage of carriers to a continuous state, improving the gain, and facilitating the realization of high-power output.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum cascade lasers, in particular to a quantum cascade laser with a novel energy band structure. Background Art

[0002] Quantum cascade lasers (QCLs) are unipolar semiconductor lasers based on intersubband electron transitions in coupled quantum wells. They are an innovative product that combines quantum band engineering and molecular beam epitaxy. QCLs offer advantages such as a wide tunable wavelength range, unipolarity, a cascade structure, short relaxation times, and negligible intersubband Auger recombination. With the continuous development of QCL technology, it has achieved practical application in the following sub-sectors:

[0003] (1) Photoelectric countermeasure systems. The laser emitted by QCL overlaps with the response band of the detector, which can cause in-band damage or interference to the detector, rendering it inoperable. With the increasing use of infrared focal plane array detectors, the demand for laser sources in the medium and long wavelength bands is becoming increasingly urgent. Replacing solid-state lasers with QCL light sources currently represents the future development direction of light sources for the United States' directional countermeasure systems.

[0004] (2) Gas detection applications. Mid-infrared QCLs are used in global warming and ozone depletion research on important carbon-based gases (CO, CO2, CH4, and H2CO), industrial emission measurements, and medical diagnostics for biomarker detection and monitoring (such as NO2, NO, CO, CO2, NH3, C2H6, and CS2). In the future, selective surgery may also be performed by cauterizing specific cell types based on their chemical or protein content.

[0005] (3) Free-space optical communications. Considering information capacity and system cost, QCLs are the most advantageous information carriers. These systems have good bandwidth and are cheaper to install than fiber optic cables.

[0006] Social demand is the driving force behind scientific and technological progress. Mid- and long-wavelength QCLs, with their compact size, real-time, remote, high-resolution, high-sensitivity, and wide-spectral continuous single-mode tuning, hold significant practical value in applications such as online real-time monitoring of climate change and environmental pollution, non-invasive medical diagnostics, national security, and secure atmospheric communications, as well as in strategic emerging industries. Future QCL development will continue to focus on high output power. The development of high-power QCLs lags significantly behind domestic and international standards. The highest output power in China has just broken the watt mark (compared to the world's most advanced single-tube output power exceeding 5W). While some technological breakthroughs have been achieved, significant gaps remain to be filled, and commercialization is still a long way off. Currently, mid- and long-wavelength QCLs are limited by two major technical challenges: low electro-optical conversion efficiency and severe heat accumulation, resulting in a development bottleneck of low device power. Key approaches to overcoming these challenges are band structure design, epitaxial material growth, and device processing. The band structure design leverages the theory of active region population inversion and gain to provide a scientific basis and theoretical guidance for the innovative conduction band structure in the QCL active region, resulting in a substantial leap forward and a milestone in QCL high-power performance. This urgent need for high-power QCLs, coupled with the highly targeted, short iteration cycle, and strong practicality of band engineering, served as the driving force behind this patent application.

[0007] In 1994, Faist et al. at Bell Labs in the United States successfully designed the world's first quantum cascade laser, achieving a 4.2μm lasing wavelength and a peak output power of 8mW in pulsed mode. This first QCL employed a triple-well coupled single-phonon resonant tunneling oblique transition structure and a graded superlattice structure in the active and injection regions, respectively. The energy gap between the lower lasing levels 3 and 2 was designed to be a longitudinal optical phonon (E32 = 32meV), significantly reducing the lifetime of the lower lasing level (~0.2ps) and the upper lasing level lifetime to 1ps, thereby achieving a population inversion between energy levels 4 and 3. However, this single-phonon structure resulted in significant power degradation as the operating temperature rose to room temperature. To address the issue of low device power, confinement to continuum, two-phonon resonance, shallow-well active region structures, and excited-state injection active region structures have emerged. These structures insert lower energy levels within the lower energy levels, suppressing backscattering and reducing heat accumulation, all of which have achieved relatively good results in increasing output power.

[0008] Later, researchers discovered that the electron injection efficiency of the upper lasing level 4 in the active region of a quantum cascade laser (QCL) is one of the bottlenecks limiting performance improvements, including device output power. This is because injection efficiency directly affects many laser properties, including slope efficiency, transparency current density, and thermal characteristics. Carrier leakage analysis based on rate equation models revealed that electron escape to parasitic level 5 and subsequent scattering to other energy levels is the primary mechanism for QCL electron leakage. To improve injection efficiency, they employed a method to increase the energy gap between the upper lasing level 4 and the parasitic level 5 above it, hoping to separate level 4 from other energy levels, improve the efficiency of electron injection into level 4, and increase output power. Ultimately, results showed that this structure achieved an E54 of up to 90 meV. In 2011, the team achieved electro-optical conversion efficiencies of 27% in pulsed and 21% in continuous-wave operation, respectively, at a lasing wavelength of 4.9 μm. Its maximum single-sided continuous-wave output power at room temperature exceeded 5 W for the first time. Summary of the Invention

[0009] In order to solve the technical problems of low energy gap between lasing energy level and parasitic energy level, high electron leakage and low injection efficiency in the prior art quantum cascade laser, an object of the present invention is to provide a quantum cascade laser with a novel energy band structure, the quantum cascade laser comprising:

[0010] InP substrate, and an injection region and an active region prepared on the InP substrate, wherein:

[0011] The injection region includes:

[0012] first AlAs layer, first AlInAs layer, first GaInAs layer, second AlInAs layer,

[0013] The second AlAs layer, the third AlInAs layer, the second GaInAs layer, the fourth AlInAs layer,

[0014] The third AlAs layer, the fifth AlInAs layer, the third GaInAs layer, the sixth AlInAs layer,

[0015] The fourth AlAs layer, the seventh AlInAs layer, the fourth GaInAs layer, the eighth AlInAs layer,

[0016] The fifth AlAs layer, the ninth AlInAs layer, the fifth GaInAs layer, the tenth AlInAs layer,

[0017] The sixth AlAs layer, the eleventh AlInAs layer, the sixth GaInAs layer, the twelfth AlInAs layer,

[0018] a seventh AlAs layer and a thirteenth AlInAs layer;

[0019] The active region comprises:

[0020] the seventh GaInAs layer, the fourteenth AlInAs layer, the eighth GaInAs layer, the fifteenth AlInAs layer, the sixteenth AlInAs layer, the ninth GaInAs layer,

[0021] InAs layer,

[0022] tenth GaInAs layer, seventeenth AlInAs layer, eighteenth AlInAs layer, nineteenth AlInAs layer,

[0023] an eleventh GaInAs layer, a twelfth GaInAs layer, a thirteenth GaInAs layer, and a twentieth AlInAs layer.

[0024] Furthermore, n-type doping is performed on the third GaInAs layer, the sixth AlInAs layer, the fourth AlAs layer, the seventh AlInAs layer, the fourth GaInAs layer, the eighth AlInAs layer, the fifth AlAs layer, and the ninth AlInAs layer in the injection region, with a doping concentration of 2×10 17 cm -3 .

[0025] The invention provides a quantum cascade laser with a novel energy band structure, which further increases the energy interval between the upper lasing energy level and the parasitic energy level, reduces electron leakage, and improves injection efficiency.

[0026] The present invention provides a quantum cascade laser with a novel energy band structure. To address the problem of low power output of quantum cascade lasers, a deep potential well is nested in a shallow well in the active region, and a high potential barrier is nested in a high potential barrier in the injection region. This significantly reduces the leakage of carriers to the continuous state, improves the gain, and is conducive to achieving high-power output.

[0027] The present invention provides a quantum cascade laser with a novel energy band structure. The shallow-well high-barrier structure is used as the basis of the entire energy band architecture. An InAs layer is inserted in the middle of the second quantum well in the active area as a deep potential well, and an AlAs high-barrier layer is inserted in the barrier layer in the injection area. The thickness of each barrier layer and potential well layer is adjusted and optimized to meet various requirements such as lasing wavelength, electron leakage, and gain.

[0028] The present invention provides a quantum cascade laser with a novel energy band structure. The optimized energy band structure increases the output peak gain to over 120 at an output wavelength of 4.6 μm, a 50% increase in gain over the band structure with the highest room-temperature electro-optical conversion efficiency reported internationally. This improves injection efficiency and optimizes voltage defects to achieve high-power output in the mid-wave infrared. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 The schematic diagram of the structure of the quantum cascade laser with a novel energy band structure of the present invention is shown schematically.

[0031] Figure 2 A schematic structural diagram of the injection region of the present invention is shown.

[0032] Figure 3 FIG. 4 shows a schematic structural diagram of the active region of the present invention.

[0033] Figure 4 The schematic diagram shows the principle of the quantum cascade laser with a novel energy band structure of the present invention.

[0034] Figure 5 A schematic diagram of injection region definition during simulation in one embodiment of the present invention is shown.

[0035] Figure 6 A schematic diagram of active area definition during simulation in one embodiment of the present invention is shown.

[0036] Figure 7 A schematic diagram of a shallow-well, high-barrier, deep-potential-well, single-period energy band structure of a quantum cascade laser with a novel energy band structure according to the present invention is shown.

[0037] Figure 8 A schematic diagram of the complete energy band structure of the shallow well, high barrier and deep potential well of the quantum cascade laser with a novel energy band structure of the present invention is shown.

[0038] Figure 9 The graph shows the gain output results of the quantum cascade laser with a novel energy band structure of the present invention. DETAILED DESCRIPTION

[0039] In order to make the above and other features and advantages of the present invention more clear, the present invention is further described below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.

[0040] In order to solve the technical problems of low energy gap between the lasing energy level and the parasitic energy level, high electron leakage and low injection efficiency in the existing quantum cascade laser, and in view of the urgent demand for high-power medium-wave infrared band, the electron injection efficiency of the lasing energy level in the active region is a bottleneck that limits the improvement of device output power and other performance. Previously, the main approach was to insert a lower energy level into the low energy level to suppress backscattering and reduce heat accumulation; increase the energy gap between the upper lasing energy level and the parasitic energy level above it, hoping to separate the upper lasing energy level from other energy levels and improve the efficiency of electron injection into the next energy level.

[0041] The present invention proposes to insert InAs material into the active region to form a deep potential well, thereby increasing the output peak gain to more than 120 and effectively increasing the power output. Figure 1 The schematic diagram of the structure of the quantum cascade laser with a novel energy band structure of the present invention is shown. Figure 2 The structural diagram of the injection region of the present invention is shown in FIG. Figure 3 The structure diagram of the active region of the present invention is shown. According to an embodiment of the present invention, a quantum cascade laser with a novel energy band structure is proposed, including: an InP substrate 100, and an injection region 200 and an active region 300 prepared on the InP substrate 100.

[0042] The implantation region 200 includes:

[0043] first AlAs layer 201, first AlInAs layer 202, first GaInAs layer 203, second AlInAs layer 204,

[0044] The second AlAs layer 205, the third AlInAs layer 206, the second GaInAs layer 207, the fourth AlInAs layer 208,

[0045] The third AlAs layer 209, the fifth AlInAs layer 210, the third GaInAs layer 211, the sixth AlInAs layer 212,

[0046] The fourth AlAs layer 213, the seventh AlInAs layer 214, the fourth GaInAs layer 215, the eighth AlInAs layer 216,

[0047] The fifth AlAs layer 217, the ninth AlInAs layer 218, the fifth GaInAs layer 219, the tenth AlInAs layer 220,

[0048] The sixth AlAs layer 221, the eleventh AlInAs layer 222, the sixth GaInAs layer 223, the twelfth AlInAs layer 224,

[0049] a seventh AlAs layer 225 and a thirteenth AlInAs layer 226 .

[0050] The active area 300 includes:

[0051] a seventh GaInAs layer 301, a fourteenth AlInAs layer 302, an eighth GaInAs layer 303, a fifteenth AlInAs layer 304, a sixteenth AlInAs layer 305, a ninth GaInAs layer 306, an InAs layer 307, a tenth GaInAs layer 308, a seventeenth AlInAs layer 309, an eighteenth AlInAs layer 310, a nineteenth AlInAs layer 311, an eleventh GaInAs layer 312, a twelfth GaInAs layer 313, a thirteenth GaInAs layer 317, and a twentieth AlInAs layer 315.

[0052] According to an embodiment of the present invention, n-type doping is performed on the third GaInAs layer 211, the sixth AlInAs layer 212, the fourth AlAs layer 213, the seventh AlInAs layer 214, the fourth GaInAs layer 215, the eighth AlInAs layer 216, the fifth AlAs layer 217, and the ninth AlInAs layer 218 of the injection region 200, with a doping concentration of 2×10 17 cm -3 .

[0053] like Figure 4 The figure shows a schematic diagram of the principle of a quantum cascade laser with a novel energy band structure of the present invention. The energy band engineering of the QCL quantum cascade laser is to combine and utilize multiple semiconductor materials with different conduction band bottom energies to produce different band orders, form coupled quantum wells, and then use electron transitions and quantum effects to achieve particle population inversion; the cascade structure is used to achieve the reuse of one electron and sequential tunneling. In theory, one electron can emit photons with the same number of photons, realizing single electron injection and multi-photon output, which is conducive to high-power lasing.

[0054] The energy band structure of a QCL quantum cascade laser consists of an active region and an injection region. The injection region enables rapid electron extraction and injection. The active region employs a four-level system, where electrons undergo radiative transitions and release photons. These two regions work together to achieve population inversion. The active region primarily undergoes two processes: stimulated emission and radiative transitions. Electrons rapidly relax to the ground state through resonant transport, and then tunnel into the microstrip structure of the injection region through phonon-assisted tunneling.

[0055] Under bias conditions, the conduction band edge of the superlattice tilts, and a cascade structure is formed between the sub-band energy levels. By repeating the periodic physical process of extracting electrons from the injection region and emitting photons from the active region, the multi-cascade periodic structure realizes multi-photon output.

[0056] The active region in the energy band structure of the present invention mainly includes two processes: stimulated radiation and radiative transition. Among them, electrons at high energy level 3 reach low energy level 2 through stimulated radiation and release a photon. The process from energy level 2 to 1 is a non-radiative transition. After that, they quickly relax to the ground state energy level through resonant transport, and then tunnel to the microstrip structure of the injection region through phonon assistance. The present invention designs two LO phonons (longitudinalooptical, longitudinal optical phonons) with an energy (about 64meV) between energy levels 2 and 3 to quickly empty electrons, making the lifetime of energy level 2 much shorter than that of energy level 3, achieving population inversion. The injection region has a permeability-enhancing effect on electrons on low energy level 1, accelerating the resonant tunneling process and increasing electron extraction efficiency; it has a reflective effect on electrons on high energy level 3, inhibiting their escape and leakage to high energy states and increasing carrier injection efficiency.

[0057] The invention is based on an InP-based AlInAs / GaInAs system, wherein the active region adopts a superlattice structure in which a lattice-matched InGaAs shallow well is inserted into an InAs deep potential well layer, and the injection region is nested in an InAlAs high potential barrier layer and an AlAs high potential barrier layer is inserted.

[0058] The present invention is simulated and calculated in one embodiment as follows.

[0059] (1) Define materials: Use different numbers to define the corresponding InP-based AlInAs / GaInAs material system to obtain the material library. Use numbers 1-6 to mark Ga 0.47 In 0.53 As、Al 0.48 In 0.52 As、Ga 0.31 In 0.69 As、Al 0.64 In 0.36 As, AlAs, InAs.

[0060] (2) Define the injection region: The injection region contains Ga 0.31 In 0.69 As、Al 0.64 In 0.36 As, AlAs three materials (respectively marked with numbers 3, 4, 5), the injection area has a total of 26 layers of materials, such as Figure 5 FIG. 1 is a schematic diagram showing the definition of the injection region during the simulation process in one embodiment of the present invention.

[0061] (3) Define the active region: The active region contains Ga 0.47 In 0.53 As、Al 0.48 In 0.52 As、Ga 0.31 In 0.69 As、Al0.64 In 0.36 There are five materials, As, AInAs (respectively marked with numbers 1, 2, 3, 4, and 6), and a total of 15 layers of materials in the active area. In order to balance the strain and achieve maximum gain output, the thickness of each layer in the active area is defined with the corresponding material after debugging iterations, such as Figure 6 FIG. 1 is a schematic diagram showing the definition of active areas during simulation in one embodiment of the present invention.

[0062] (4) Single-period band structure: According to an embodiment of the present invention, n-type doping is performed on layers 11-18 in the injection region structure, with a doping concentration of 2×10 17 cm -3 , increasing the electron transport capacity of the injection region. Then an external electric field E is added field =120kV / cm, and a shallow well, high barrier, deep well, single-period band structure is obtained, such as Figure 7 The figure shows a schematic diagram of a single-period energy band structure of a quantum cascade laser with a shallow well, high potential barrier and deep potential well of the present invention having a novel energy band structure.

[0063] (5) Complete band structure: The number of periods increases to 3, and finally all wave functions are solved to obtain the complete band structure diagram of the shallow well, high barrier and deep potential well of the quantum cascade laser. The simulation results show that when the output wavelength is 4.6μm, the peak gain reaches more than 120. Figure 8 The schematic diagram of the complete energy band structure of the quantum cascade laser with a shallow well, high potential barrier and deep potential well of the present invention with a novel energy band structure is shown. Figure 9 The figure shows the gain output result of the quantum cascade laser with a novel energy band structure of the present invention.

[0064] The above simulation calculations verify that in terms of improving the injection efficiency, the design of the shallow well active region and the high potential barrier relaxation / injection region of the present invention increases the band gap between energy level 4 and energy level 3 to 60meV, and the presence of energy level 5 will also reduce the leakage of high-energy state electrons in the laser transition, thereby improving the injection efficiency of electrons to the next energy level, and the peak output gain reaches more than 120.

[0065] In terms of optimizing voltage defects, the shallow well active region and high potential barrier increase the voltage defect between the low energy state of laser transition and the chirped superlattice microstrip in the subsequent relaxation / injection region to 140meV, which not only improves the injection efficiency but also greatly reduces the carrier thermal backfill effect.

[0066] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A quantum cascade laser with a novel band structure, characterized in that: The quantum cascade laser comprises: InP substrate, and an injection region and an active region prepared on the InP substrate, wherein: The injection region includes: first AlAs layer, first AlInAs layer, first GaInAs layer, second AlInAs layer, The second AlAs layer, the third AlInAs layer, the second GaInAs layer, the fourth AlInAs layer, The third AlAs layer, the fifth AlInAs layer, the third GaInAs layer, the sixth AlInAs layer, The fourth AlAs layer, the seventh AlInAs layer, the fourth GaInAs layer, the eighth AlInAs layer, The fifth AlAs layer, the ninth AlInAs layer, the fifth GaInAs layer, the tenth AlInAs layer, a sixth AlAs layer, an eleventh AlInAs layer, a sixth GaInAs layer, a twelfth AlInAs layer, a seventh AlAs layer, and a thirteenth AlInAs layer; The active region comprises: the seventh GaInAs layer, the fourteenth AlInAs layer, the eighth GaInAs layer, the fifteenth AlInAs layer, the sixteenth AlInAs layer, the ninth GaInAs layer, InAs layer, tenth GaInAs layer, seventeenth AlInAs layer, eighteenth AlInAs layer, nineteenth AlInAs layer, an eleventh GaInAs layer, a twelfth GaInAs layer, a thirteenth GaInAs layer, and a twentieth AlInAs layer.

2. The quantum cascade laser according to claim 1, characterized in that The third GaInAs layer, the sixth AlInAs layer, the fourth AlAs layer, the seventh AlInAs layer, the fourth GaInAs layer, the eighth AlInAs layer, the fifth AlAs layer, and the ninth AlInAs layer in the injection region are n-doped to a doping concentration of 2×10 17 cm -3 .

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