Active Region and Quantum Cascade Laser

Abstract

The present disclosure provides an active region and a quantum cascade laser. The active region includes a plurality of periodically cascaded active cores. Each period of the active core includes a gain region and an injection region. The gain region includes four gain region quantum wells and three gain region quantum barriers. Each gain region quantum barrier is disposed between two adjacent gain region quantum wells. Among the four gain region quantum wells, the thickness of the first gain region quantum well disposed at the upper part is the smallest; the thickness of the second gain region quantum well is the largest; the thicknesses of the second gain region quantum well to the fourth gain region quantum well gradually decrease; the difference between the second gain region quantum well and the third gain region quantum well is less than the difference between the third gain region quantum well and the fourth gain region quantum well, so that the additional energy levels in the first miniband partially extend into the injection region, the additional energy levels are coupled with the laser lower energy level, and the electrons injected into the laser upper energy level radiatively transition to the laser lower energy level and the additional energy levels in vertical transition and skew transition manners respectively, and laser is generated.

Description

Technical Field

[0001] The present disclosure relates to the technical field of mid-infrared semiconductor optoelectronic devices, and in particular to an active region and a quantum cascade laser. Background Art

[0002] Quantum cascade lasers (QCLs) have wavelengths covering two atmospheric windows and have advantages such as small size and portability. They have important applications in gas detection, space communications and other fields. At present, the room temperature continuous wave output power of quantum cascade lasers in the 4-5um band has exceeded 5W. This band is set in the atmospheric window and the active area design is optimized, so the output power is relatively high; in the band outside the atmospheric window, due to severe water vapor absorption and the active area structure that needs to be optimized, there are few reports of high-power QCLs. In addition, as the wavelength increases, it is more difficult to achieve high-power output. This is mainly due to the following two reasons: First, the longer the wavelength, the smaller the energy level interval in the microstrip, and the more intense the non-radiative transition between the upper and lower energy levels of the laser. In order to maintain the population inversion, long-wave and very long-wave lasers often use an active area design with oblique transitions or partial oblique transitions, which will cause the transition matrix element corresponding to the stimulated radiation to become smaller, resulting in insufficient peak gain. At the same time, due to the shortened energy level interval in the microstrip, thermal backfill and heat leakage are also aggravated compared to medium-wave QCLs. The second reason is that free carrier absorption is proportional to wavelength, so the waveguide loss of long-wave QCL will be greater. Driven by the needs of some special fields (such as long-distance transmission of free-space laser communication, etc.), it is imperative to develop mid- and long-wave infrared QCLs that take into account both tuning range and output power.

[0003] In the prior art, the highest room temperature continuous wave average output power of mid-infrared QCLs with a wavelength of around 7um can reach 1.4W. Among them, the three-phonon resonance extraction active region structure can further accelerate the extraction efficiency of carriers in the laser lower energy level and reduce the carrier lifetime in the laser lower energy level compared to the traditional single-phonon and double-phonon active region structures. However, the disadvantage of this type of structure is that it has great restrictions on the thickness of the active region quantum well and injection barrier, and it is impossible to obtain wide gain while obtaining high peak gain.

[0004] In order to obtain a wide tuning range, the active region structure must also be redesigned to make its gain spectrum wider. A common wide tuning active region design is the Bound-to-Continue (B-to-C) structure. Each period of the B-to-C structure contains multiple quantum well-quantum barrier pairs with gradually varying thicknesses, so that there are multiple lower laser energy levels with gradually decreasing transition intensities in the first microstrip. The biggest advantage of this structure is that a very wide gain spectrum can be obtained. However, this also leads to gain dispersion, making it difficult to obtain high peak gain, and therefore difficult to achieve high power output.

[0005] To simultaneously achieve high power output and a wide tuning range, it is urgently necessary to design a new active region structure with both of the above two characteristics. Summary of the Invention

[0006] To solve the technical problems in the prior art, the present disclosure provides an active region structure with a coupled lower energy level and a widely tunable, watt-level output quantum cascade laser with a central wavelength of 6.9 μm. The active region includes multiple periodically cascaded active cores, where each period of the active core includes multiple layers of quantum well-barrier pairs. The design of the active region with multiple injection energy levels and coupled transition lower energy levels enables the laser to have a wide tuning range while achieving high output power. The quantum cascade laser provided by the present disclosure has a watt-level output power and a room-temperature pulse tuning range of 6.4 μm to 7.3 μm during continuous wave operation at room temperature.

[0007] In one aspect of the embodiments of the present disclosure, an active region is provided, which includes multiple periodically cascaded active cores. Each period of the active core includes: a gain region and an injection region. The gain region includes four gain region quantum wells and three gain region quantum barriers, and each gain region quantum barrier is disposed between two adjacent gain region quantum wells. Among them, the thickness of the first gain region quantum well located at the upper part among the four gain region quantum wells is the smallest; the thickness of the second gain region quantum well is the largest; the thicknesses of the second gain region quantum well to the fourth gain region quantum well gradually decrease; the difference between the second gain region quantum well and the third gain region quantum well is less than the difference between the third gain region quantum well and the fourth gain region quantum well, so that the additional energy levels in the first miniband partially extend to the injection region, and the additional energy levels are coupled with the laser lower energy level. The electrons injected into the laser upper energy level radiatively transition to the laser lower energy level and the additional energy levels in vertical and oblique transition manners respectively, and generate laser.

[0008] According to the embodiments of the present disclosure, among the three gain region quantum barriers, the thickness of the third gain region quantum barrier is the largest, and the thicknesses of the first gain region quantum barrier and the second gain region quantum barrier are equal.

[0009] According to the embodiments of the present disclosure, the injection region includes: five injection region quantum barriers and four injection region quantum wells disposed between two adjacent injection region quantum barriers. The fifth injection region quantum barrier at the lower part of the injection region is connected to the first gain region quantum well of the next period.

[0010] According to an embodiment of the present disclosure, among the five quantum barriers in the injection region, the thickness of the fifth injection region quantum barrier is the largest; the thickness of the fourth injection region quantum barrier is less than the thickness of the fifth injection region quantum barrier and greater than the thicknesses of the quantum barriers in the other three injection regions, and the differences between the thickness of the fourth injection region quantum barrier and the thicknesses of the quantum barriers in the first, second, and third injection regions respectively are greater than the absolute values of the differences between the thicknesses of the quantum barriers in the first, second, and third injection regions themselves.

[0011] According to an embodiment of the present disclosure, the third injection region quantum well in the four injection region quantum wells and the fourth injection region quantum barrier in the five injection region quantum barriers are doped layers, and the doping concentration range includes 1.5×10 17 cm -3 ~2.5×10 17 cm -3 , and the doping atom is Si.

[0012] Another aspect of the embodiments of the present disclosure provides a quantum cascade laser, including: a substrate; a lower waveguide layer disposed on the substrate; any one of the active regions as described above disposed on the lower waveguide layer; an optical confinement layer disposed on the active region; an upper waveguide layer disposed on the optical confinement layer; and an ohmic contact layer disposed on the upper waveguide layer.

[0013] According to an embodiment of the present disclosure, the active region of the quantum cascade laser includes: a first active region disposed on the lower waveguide layer; and a second active region disposed on the first active region. The difference range of the quantum barrier strain values between the first active region and the second active region includes 0.05% to 0.1% to limit the difference in peak gain between the first active region and the second active region.

[0014] According to an embodiment of the present disclosure, the first active region includes 15 to 30 periodically cascaded first active cores.

[0015] According to an embodiment of the present disclosure, the second active region includes 15 to 30 periodically cascaded second active cores.

[0016] According to an embodiment of the present disclosure, the quantum cascade laser further includes two etched regions disposed at intervals to divide the vertical structure formed by the active region, the optical confinement layer, the upper waveguide layer, and the ohmic contact layer into three regions; wherein, InP is filled in the two etched regions to confine the laser to the middle region for lasing.

[0017] According to an embodiment of the present disclosure, by increasing the thickness of the quantum wells in the first and second gain regions, the additional energy levels that originally did not participate in lasing in the first miniband are partially extended to the injection region. The additional energy levels will couple with the laser lower energy level, and the electrons injected into the laser upper energy level radiatively transition to the laser lower energy level and the additional energy level in vertical and oblique transition manners respectively. Compared with the B-to-C structure, for the active region structure provided by the present disclosure, on the one hand, it is because there are partial oblique transitions, and on the other hand, it is because the number of electrons in the lower energy level is smaller. Therefore, the lifetime of the upper energy level is longer. A longer lifetime of the upper energy level is beneficial to obtaining a stronger population inversion degree, and ultimately obtaining a high peak gain and improving the output power. Compared with the design scheme in the B-to-B active region structure that only contains one laser lower energy level, the coupled laser lower energy level structure can obtain a wider gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematically shows a structural diagram of an active core for one period according to an embodiment of the present disclosure;

[0019] Figure 2 Schematically shows a band structure diagram of one period of an active region according to an embodiment of the present disclosure;

[0020] Figure 3 Schematically shows a structural diagram of a quantum cascade laser according to an embodiment of the present disclosure;

[0021] Figure 4 Schematically shows a structural diagram of one period of a first active core and a second active core according to an embodiment of the present disclosure;

[0022] Figure 5 Schematically shows the XRD test results and fitting results of an active region according to an embodiment of the present disclosure;

[0023] Figure 6 Schematically shows a tuning range diagram of an external cavity mode during room temperature pulsed operation of a laser according to an embodiment of the present disclosure; and

[0024] Figure 7 Schematically shows a room temperature continuous current-voltage-power (P-I-V) curve diagram of a laser according to an embodiment of the present disclosure.

[0025] DESCRIPTION OF REFERENCE NUMERALS:

[0026] 1 - Substrate;

[0027] 2 - Lower waveguide layer;

[0028] 3 - Active region;

[0029] 31 - First active region;

[0030] 32 - Second active region;

[0031] 4 - Light limiting layer;

[0032] 5 - Upper waveguide layer;

[0033] 6 - Ohmic contact layer. Detailed implementation manners

[0034] To make the objectives, technical solutions and advantages of the present disclosure clearer and more understandable, the following further describes the present disclosure in detail with reference to specific embodiments and the accompanying drawings. However, the present disclosure can be implemented in different forms and should not be construed as limited to the embodiments presented herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0035] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0036] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0037] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0038] To facilitate the understanding of the technical solutions of the present disclosure by those skilled in the art, the following technical terms are explained.

[0039] In the case of using expressions such as "at least one of A, B, and C, etc.", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, and C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, or C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0040] Figure 1 Schematically shows a schematic diagram of the structure of an active core in one period according to an embodiment of the present disclosure, Figure 2 Schematically shows a schematic diagram of the energy band structure of one period of the active region according to an embodiment of the present disclosure.

[0041] One aspect of the present disclosure provides an active region 3, and the active region includes a plurality of periodically cascaded active cores. As Figure 1 and Figure 2 shown, each period of the active core includes: a gain region 311 and an injection region 312. The gain region 311 includes four gain region quantum wells and three gain region quantum barriers, and each gain region quantum barrier is disposed between two adjacent gain region quantum wells. Among them, the thickness of the first gain region quantum well 3111 disposed in the upper part of the four gain region quantum wells is the smallest, the thickness of the second gain region quantum well 3113 is the largest, and the thicknesses of the second gain region quantum well 3113 to the fourth gain region quantum well 3117 gradually decrease. The difference between the second gain region quantum well 3113 and the third gain region quantum well 3115 is less than the difference between the third gain region quantum well 3115 and the fourth gain region quantum well 3117, so that a part of the additional energy level n2 in the first miniband extends to the injection region, the additional energy level n2 is coupled with the laser lower energy level n1, and the electrons injected into the laser upper energy level n3 radiatively transition to the laser lower energy level n1 and the additional energy level n2 in vertical and oblique transition manners respectively, and generate laser.

[0042] According to an embodiment of the present disclosure, as Figure 1 and Figure 2As shown, by increasing the thicknesses of the quantum wells 3111 in the first gain region and the quantum wells 3113 in the second gain region, part of the additional energy level n2 that originally did not participate in lasing within the first miniband extends into the injection region. The additional energy level n2 will couple with the laser lower energy level n1, and the electrons injected into the laser upper energy level n3 radiatively transition to the laser lower energy level n1 and the additional energy level n2 in vertical and oblique transition manners respectively. Compared with the B-to-C structure, for the active region structure provided by the present disclosure, on the one hand, it is because there are partial oblique transitions, and on the other hand, it is because the number of electrons in the laser lower energy level n1 is smaller. Therefore, the lifetime of the upper energy level n3 is longer. A longer lifetime of the upper energy level n3 is beneficial to obtaining a stronger population inversion degree, ultimately obtaining a high peak gain and improving the output power. Compared with the design scheme in the B-to-B active region structure that only contains one laser lower energy level n1, the coupled laser lower energy level n1 structure can obtain a wider gain.

[0043] According to an embodiment of the present disclosure, the active region 3 is composed of multiple quantum well - quantum barrier layers, and the multiple quantum well - quantum barrier layers are In x Ga 1-x As - In y Al 1-y As, where 0 < x < 1 and 0 < y < 1.

[0044] In a schematic embodiment, the quantum wells of the active core all include In 0.6 Ga 0.4 As.

[0045] In a schematic embodiment, the quantum barriers of the active core all include In 0.378 Al 0.622 As.

[0046] According to an embodiment of the present disclosure, the energy level represents the energy value that a microscopic particle system has when it is in each stable energy state.

[0047] According to an embodiment of the present disclosure, the lasing wavelength of the quantum cascade laser is determined by the energy level spacing between subbands in the conduction band, and the energy level spacing between subbands can be changed by adjusting the thickness of the quantum well / barrier layer, thereby changing the lasing wavelength of the quantum cascade laser.

[0048] According to an embodiment of the present disclosure, the difference range between the second gain region quantum wells 3113 and the third gain region quantum wells 3115 includes The difference range between the third gain region quantum wells 3115 and the fourth gain region quantum wells 3117 includes The difference range between these two differences includes

[0049]

[0050] In a schematic embodiment, the difference between the second gain region quantum well 3113 and the third gain region quantum well 3115 is The difference between the third gain region quantum well 3115 and the fourth gain region quantum well 3117 is The difference between these two differences is According to an embodiment of the present disclosure, as Figure 1 shown, among the three gain region quantum barriers, the thickness of the third gain region quantum barrier 3116 is the largest, and the thickness of the first gain region quantum barrier 3112 is equal to the thickness of the second gain region quantum barrier 3114.

[0051] According to an embodiment of the present disclosure, the injection region includes five injection region quantum barriers and four injection region quantum wells disposed between two adjacent injection region quantum barriers. The fifth injection region quantum barrier 3129 at the lower part of the injection region is connected to the first gain region quantum well of the next period.

[0052] According to an embodiment of the present disclosure, among the five quantum barriers of the injection region, the thickness of the fifth injection region quantum barrier 3129 is the largest; the thickness of the fourth injection region quantum barrier 3127 is less than the thickness of the fifth injection region quantum barrier 3129 and greater than the thicknesses of the other three injection region quantum barriers, and the differences between the thickness of the fourth injection region quantum barrier 3127 and the thicknesses of the first injection region quantum barrier 3121, the second injection region quantum barrier 3123, and the third injection region quantum barrier 3125 are greater than the absolute value of the difference between the thicknesses of the first injection region quantum barrier 3121, the second injection region quantum barrier 3123, and the third injection region quantum barrier 3125.

[0053] According to an embodiment of the present disclosure, the injection region includes multiple injection energy levels.

[0054] According to an embodiment of the present disclosure, the third injection region quantum well 3126 among the four injection region quantum wells and the fourth injection region quantum barrier 3127 among the five injection region quantum barriers are doped layers, and the doping concentration range includes 1.5×10 17 cm -3 ~2.5×10 17 cm -3 , and the doping atom is Si.

[0055] In a schematic embodiment, the third injection region quantum well 3126 among the four injection region quantum wells and the fourth injection region quantum barrier 3127 among the five injection region quantum barriers are doped layers, and the doping concentration is both 2.0×10 17 cm -3 , and the doping atom is Si.

[0056] In a schematic embodiment, the third injection region quantum well 3126 among the four injection region quantum wells and the fourth injection region quantum barrier 3127 among the five injection region quantum barriers are doped layers, and the doping concentration is 1.7×10 17 cm -3 , and the doping atoms are Si. Figure 3 Schematically shows a structural schematic diagram of a quantum cascade laser according to an embodiment of the present disclosure.

[0057] Another aspect of the embodiments of the present disclosure provides a quantum cascade laser, as Figure 3 shown, the quantum cascade laser includes: a substrate 1, a lower waveguide layer 2, any one of the above active regions 3, an optical confinement layer 4, an upper waveguide layer 5, and an ohmic contact layer 6. The lower waveguide layer 2 is disposed on the substrate 1, the active region 3 is disposed on the lower waveguide layer 2, the optical confinement layer 4 is disposed on the active region 3, the upper waveguide layer 5 is disposed on the optical confinement layer 4, and the ohmic contact layer 6 is disposed on the upper waveguide layer 5.

[0058] According to an embodiment of the present disclosure, the substrate 1 is an n-type doped InP, and the doping concentration range includes 0.2×10 17 cm -3 ~5×10 17 cm -3 , and the thickness range includes 300um~350um.

[0059] According to an embodiment of the present disclosure, the lower waveguide layer 2 is an n-type doped InP, and the doping concentration range includes 2×10 16 cm -3 ~4×10 16 cm -3 , and the thickness range includes 2um~2.5um.

[0060] According to an embodiment of the present disclosure, the thickness range of the active layer 3 includes 2um~2.1um.

[0061] In a schematic embodiment, the thickness range of the active layer 3 is 2.05um.

[0062] According to an embodiment of the present disclosure, the material of the optical confinement layer 4 includes In z Ga 1-z As, where 0<z<1.

[0063] In a schematic embodiment, the material of the optical confinement layer 4 is In 0.53 Ga 0.47 As.

[0064] According to an embodiment of the present disclosure, the optical confinement layer 4 is n-type doped, and the doping concentration is 2×10 16 cm -3 ~3×1016 cm -3 The layer thickness is 0.4 um to 0.6 um.

[0065] According to an embodiment of the present disclosure, the upper waveguide layer 5 is n-type doped InP with a doping concentration of 3×10 16 cm -3 ~4×10 16 cm -3 ,and the layer thickness is 3 um to 3.5 um.

[0066] According to an embodiment of the present disclosure, the ohmic contact layer 6 is n-type doped InP with a doping concentration of 0.5×10 18 cm -3 ~5×10 18 cm -3 ,and the layer thickness is 0.8 um to 1 um.

[0067] According to an embodiment of the present disclosure, as Figure 3 shown, the active region 3 of the quantum cascade laser includes: a first active region 31 and a second active region 32. The first active region 31 is disposed on the lower waveguide layer 2, and the second active region 32 is disposed on the first active region 31. The difference range of the quantum barrier strain values between the first active region 31 and the second active region 32 includes 0.05% to 0.1%, so as to limit the difference in peak gain between the first active region 31 and the second active region 32, which can avoid a large difference in peak gain between the first active region 31 and the second active region 32 and reduce the output power. At the same time, compared with the single-core structure, a wider gain can be obtained.

[0068] In a schematic embodiment, the difference range of the quantum barrier strain values between the first active region 31 and the second active region 32 is 0.06% or 0.09%.

[0069] According to an embodiment of the present disclosure, the first active region 31 includes 15 - 30 periodically cascaded first active cores core1.

[0070] In a schematic embodiment, the first active region 31 includes 20 periodically cascaded first active cores core1.

[0071] In a schematic embodiment, the first active region 31 includes 25 periodically cascaded first active cores core1.

[0072] According to an embodiment of the present disclosure, the second active region 32 includes 15 - 30 periodically cascaded second active cores core2.

[0073] In a schematic embodiment, the second active region 32 includes 20 periodically cascaded second active cores core2.

[0074] In a schematic embodiment, the second active region 32 includes 23 second active cores core2 in periodic cascade.

[0075] According to an embodiment of the present disclosure, the number of periods of the first active region 31 is approximately equal to that of the second active region 32.

[0076] According to an embodiment of the present disclosure, as Figure 3 shown, the quantum cascade laser further includes two etched regions disposed at intervals to divide the vertical structure formed by the active region 3, the optical confinement layer 4, the upper waveguide layer 5, and the ohmic contact layer 6 into three regions. Among them, InP is filled in the two etched regions to confine the laser to the middle region for lasing.

[0077] In another embodiment, the quantum cascade laser further includes two etched regions disposed at intervals to divide the vertical structure formed by the active region 3, the optical confinement layer 4, the upper waveguide layer 5, and the ohmic contact layer 6 into three regions, and a SiO2 insulating layer is grown on the etched regions and the ohmic contact layer 6 to confine the laser to the middle region for lasing.

[0078] In a schematic embodiment, the active region 3 includes: a first active region 31 and a second active region 32. The first active region 31 includes a plurality of first active cores core1 in periodic cascade, and the second active region 32 includes a plurality of second active cores core2 in periodic cascade.

[0079] Figure 4 A schematic structural diagram of one period of the first active core and the second active core according to an embodiment of the present disclosure is schematically shown.

[0080] In a schematic embodiment, as Figure 4 shown, each period of the first active core core1 in the first active region 31 includes: a gain region and an injection region.

[0081] The gain region includes: the thicknesses of the first, second, third, and fourth gain region quantum wells are respectively and

[0082] A gain region quantum barrier is disposed between two adjacent gain region quantum wells. The thicknesses of the first, second, and third gain region quantum barriers are respectively and

[0083] Below the gain region is the injection region, and the injection region includes:

[0084] The thicknesses of the first, second, third, fourth, and fifth injection region quantum barriers are respectively and The first barrier of the injection region is connected to the fourth quantum well of the gain region;

[0085] An injection region quantum well is provided between two adjacent injection region barriers: the first, second, third, and fourth injection region quantum wells, with thicknesses of and The fifth injection region quantum barrier is connected to the first gain region quantum well of the next period.

[0086] The quantum wells in the first active core all include In x Ga 1-x As, where x = 0.598. The barriers in the first active core all include In y Al 1-y As, where y = 0.422. Specifically, the first active layer is composed of In 0.598 Ga 0.402 As-n 0.422 Al 0.578 As, and the thickness of the first active layer is 1.058 um.

[0087] As Figure 4 shown, each period of the second active core core2 in the second active region 32 includes: a gain region and an injection region.

[0088] The gain region includes: the first, second, third, and fourth gain region quantum wells, with thicknesses of and

[0089] A gain region quantum barrier is provided between two adjacent gain region quantum wells: the first, second, and third gain region barriers, with thicknesses of and

[0090] Below the gain region is the injection region, which includes:

[0091] The first, second, third, fourth, and fifth injection region quantum barriers, with thicknesses of and The first injection region quantum barrier is connected to the fourth gain region quantum well.

[0092] An injection region quantum well is provided between two adjacent injection region quantum barriers: the first, second, third, and fourth injection region quantum wells, with thicknesses of and The fifth injection region quantum barrier is connected to the first gain region quantum well of the next period.

[0093] The quantum wells in the second active core all include In x Ga 1-xAs, where x = 0.598, and the barriers in the second active core all include In y Al 1-y As, where y = 0.412. Specifically,

[0094] The second active layer is composed of In 0.598 Ga 0.402 As - In 0.412 Al 0.588 As, and the thickness of the first active layer is 1.066 um.

[0095] In the injection region, the third quantum well and the fourth barrier in the injection region are both set as doped layers, and the doping concentration is 2×10 17 cm -3 , and the doping atom is Si.

[0096] The strain difference between the quantum barriers in the injection regions of the first active region 31 and the second active region 32 with respect to the substrate 1 is only 0.07%, which can avoid a large difference in the peak gain of the two active cores and reduce the output power. At the same time, compared with the single-core structure, a wider gain spectrum can be obtained.

[0097] According to an embodiment of the present disclosure, as Figure 2 shown, by increasing the thicknesses of the first and second gain region quantum wells distributed in the gain region, the additional energy level n2 that originally did not participate in lasing in the first miniband partially extends to the injection region. The additional energy level n2 will be coupled with the laser lower energy level n1, and the electrons injected into the laser upper energy level n3 radiatively transition to the laser lower energy level n1 and the additional energy level n2 in vertical and oblique transition manners respectively. When the electric field strength is 60.724 kV / cm, the transition matrix elements are 1.54 nm and 1.33 nm respectively. Compared with the B-to-C structure, on the one hand, it is because there are partial oblique transitions, and on the other hand, it is because the number of electrons in the laser lower energy level n1 is smaller, so the upper energy level n3 lifetime of the active region structure provided by the present disclosure is longer. A longer upper energy level n3 lifetime is beneficial to obtaining a stronger population inversion degree and ultimately obtaining a high peak gain. Compared with the design scheme in the B-to-B active region structure that only contains one laser lower energy level n1, the coupled laser lower energy level n1 structure can obtain a wider gain.

[0098] According to an embodiment of the present disclosure, by appropriately increasing the width of the third quantum well and decreasing the width of the fourth well in the gain region, the energy level interval ΔE between the laser upper energy level n3 and the leakage energy level n4 can be increased 43 , exceeding 60 meV. In the embodiment of the present disclosure, the energy level interval ΔE between the laser upper energy level n3 and the leakage energy level n4 43 exceeds 70 meV. A large energy level interval ΔE 43It is possible to reduce the thermal leakage of carriers in the upper energy level n3, which is particularly important at a relatively high electrical injection level and is a prerequisite for achieving high power output.

[0099] According to an embodiment of the present disclosure, multiple injection energy levels are beneficial to improving the injection efficiency, increasing the dynamic operating range, and enhancing the voltage utilization rate under high-current (current greater than 1 A) operating conditions. First, under high-current (current greater than 1 A) operating conditions, since the nuclear temperature (100 °C to 150 °C) is much higher than room temperature (around 25 °C), more electrons will be distributed in the excited states of the injection region. Therefore, compared with the traditional ground-state injection structure, a higher injection efficiency can be achieved. Thus, at a high injection level, it is more conducive to obtaining a high output power. In addition, as the bias voltage increases, the laser upper energy level n3 can complete injection with different injection energy levels in the previous cycle, so a larger dynamic range can also be obtained.

[0100] According to an embodiment of the present disclosure, when the cavity length is 6 mm and under room-temperature continuous-wave operating conditions, the threshold current is 0.64 A, the saturation current can reach 1.52 A, which is about 2.4 times the threshold current, the dynamic range of the voltage can reach 2.79 V, and when operating at room-temperature continuous wave, the highest output power can exceed 1 W. Finally, since electrons no longer need to relax to the ground state of the injection region and can be injected into the laser upper energy level n3 in the next cycle, this structure also has the advantage of low voltage defects, and low voltage defects will also bring a high voltage utilization rate. When operating at room-temperature continuous wave, the threshold voltage is approximately 12.04 V, and the voltage efficiency is about 74.6%.

[0101] Figure 5 Schematically shows the XRD test results and fitting results of the active region according to an embodiment of the present disclosure, where XRD represents X-Ray diffraction.

[0102] As Figure 5 shown, it can be seen that there are two sets of complete satellite peaks, and the satellite peaks of higher orders do not show obvious broadening, indicating a high repeatability of the active region structure. The 0th-order satellite peak closer to the substrate 1 peak represents the second active region 32, and the test results show that the period value of the second active region 32 is 42.7 nm, and the fitted period value is 42.64 nm. The 0th-order satellite peak far from the substrate 1 peak represents the first active region 31, and the test results show that the period value of the first active region 31 is 42.3 nm, and the theoretical period value is 42.31 nm. In addition, the peak positions of the satellite peaks of each order given in the test results are very close to the peak positions of the satellite peaks calculated theoretically.

[0103] Figure 6Schematically shows the external cavity tuning range of the long-wave watt-level wide-tuning laser in the pulsed operating mode (1 us, 40 kHz) in the embodiments of the present disclosure. The abscissa represents the beam, the left ordinate represents the silicidation intensity, and the right ordinate represents the peak power.

[0104] In a schematic embodiment, the cavity length of the laser is 4 mm, and the antireflection film on the front cavity surface is Al2O3 / Ge (650 mm / 50 mm). As Figure 6 shown, the tuning range of the quantum cascade laser in the embodiments of the present disclosure is from 1556 cm -1 to 1361 cm -1 (6.42 um to 7.35 um), a total of 195 cm -1 (0.93 um). The wide tuning range is related to the wide gain brought by the double active region structure with close strain and the active region structure in which the lower laser level n1 is coupled with the additional level n2. As Figure 6 shown, the peak power of the laser in this operating mode, at this time the current density is 1.14 times the threshold current density, achieving a higher output power.

[0105] Figure 7 Schematically shows the current-voltage-power (P-I-V) curve of the mid-long wave watt-level wide-tuning laser in the embodiments of the present disclosure when operating in continuous wave at room temperature. The abscissa represents the current (A), the left ordinate represents the voltage (V), and the right ordinate represents the output power (W).

[0106] In a schematic embodiment, the cavity length of the laser is 6 mm, the antireflection film on the front cavity surface is Al2O3 / Ge (650 nm / 50 nm), and the high-reflection film on the rear cavity surface is ZrO2 / TiAu / Al2O3 (200 nm / 100 nm / 100 nm). As Figure 7 shown, the appearance of the inflection point in the current-voltage (V-I) curve indicates a high degree of stimulated emission. At this time, the current channel formed inside the quantum cascade laser will greatly reduce the differential resistance of the device. The threshold voltage of the quantum cascade laser is 12.04 V, the threshold current is 0.67 A, and the maximum output power reaches 1.02 W.

[0107] So far, the embodiments of the present disclosure have been described in detail with reference to the drawings. It should be noted that the implementation manners not shown or described in the drawings or the text of the specification are all forms known to those of ordinary skill in the art and have not been described in detail. In addition, the above definitions of each element and method are not limited to the specific structures, shapes or manners mentioned in the embodiments, and those of ordinary skill in the art can make simple changes or substitutions thereto.

[0108] Based on the above description, those skilled in the art should have a clear understanding of the active region and the quantum cascade laser provided by the present disclosure.

[0109] In summary, the present disclosure provides an active region structure and a quantum cascade laser with medium and long wavelength watt-level wide tuning, having a watt-level output power and a room temperature pulse tuning range of 6.4 μm to 7.3 μm under room temperature continuous wave operation.

[0110] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are only references to the directions in the accompanying drawings and are not used to limit the protection scope of the present disclosure. Throughout the drawings, the same elements are denoted by the same or similar reference numerals. When it may cause confusion in the understanding of the present disclosure, conventional structures or configurations will be omitted, and the shapes and sizes of the components in the drawings do not reflect the actual sizes and proportions, but only illustrate the content of the embodiments of the present disclosure.

[0111] Unless otherwise known to the contrary, the numerical parameters in this specification and the appended claims are approximate values and can be changed according to the required characteristics obtained through the content of the present disclosure. Specifically, all the numbers representing the contents of components, reaction conditions, etc. used in the specification and the claims should be understood to be modified by the term "about" in all cases. Generally, the meaning it expresses is that it includes a change of ±10% in some embodiments, a change of ±5% in some embodiments, a change of ±1% in some embodiments, and a change of ±0.5% in some embodiments for a specific quantity.

[0112] The ordinal numbers used in the specification and the claims, such as "first", "second", "third", etc., are used to modify the corresponding elements. They do not themselves mean that the element has any ordinal number, nor do they represent the order of one element and another element or the order in the manufacturing method. The use of these ordinal numbers is only to clearly distinguish an element with a certain name from another element with the same name.

[0113] In addition, unless specifically described or steps that must occur in sequence, the order of the above steps is not limited to the above list and can be changed or rearranged according to the required design. And the above embodiments can be used in combination with each other or combined with other embodiments based on considerations of design and reliability, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0114] The specific embodiments described above further elaborate on the objective, technical solution, and beneficial effects of the present disclosure. It should be understood that the above description is only for the specific embodiments of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc., made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. An active region includes a plurality of periodically cascaded active cores, and each period of the active cores includes: Gain region and injection region, The gain region includes four gain region quantum wells and three gain region quantum barriers, and each gain region quantum barrier is disposed between two adjacent gain region quantum wells; Among them, the thickness of the first gain region quantum well disposed in the upper part of the four gain region quantum wells is the smallest; the thickness of the second gain region quantum well is the largest; the thicknesses of the second gain region quantum well to the fourth gain region quantum well gradually decrease; the difference between the second gain region quantum well and the third gain region quantum well is less than the difference between the third gain region quantum well and the fourth gain region quantum well, so that the additional energy level in the first miniband partially extends to the injection region, the additional energy level is coupled with the laser lower energy level, and the electrons injected into the laser upper energy level respectively radiatively transition to the laser lower energy level and the additional energy level in a vertical transition and an oblique transition manner, and generate laser.

2. The active region according to claim 1, among the three gain region quantum barriers, the thickness of the third gain region quantum barrier is the largest, and the thicknesses of the first gain region quantum barrier and the second gain region quantum barrier are equal.

3. The active region according to claim 1, the injection region includes; five injection region quantum barriers, and four injection region quantum wells disposed between two adjacent injection region quantum barriers; Among them, The fifth injection region quantum barrier at the lower part of the injection region is connected to the first gain region quantum well of the next period.

4. The active region according to claim 3, among the five quantum barriers of the injection region, the thickness of the fifth injection region quantum barrier is the largest; The thickness of the fourth injection region quantum barrier is less than the thickness of the fifth injection region quantum barrier and greater than the thicknesses of the other three injection region quantum barriers, and the differences between the thickness of the fourth injection region quantum barrier and the thicknesses of the first, second, and third injection region quantum barriers are greater than the absolute values of the differences between the thicknesses of the first, second, and third injection region quantum barriers.

5. The active region according to claim 3, wherein the third injection region quantum well among the four injection region quantum wells and the fourth injection region quantum barrier among the five injection region quantum barriers are doping layers, and the doping concentration range includes 1.5×10 17 cm -3 ~2.5×10 17 cm -3 , and the doping atom is Si.

6. A quantum cascade laser, comprising: Substrate; Lower waveguide layer disposed on the substrate; The active region according to any one of claims 1 to 5, disposed on the lower waveguide layer; Optical confinement layer disposed on the active region; Upper waveguide layer disposed on the optical confinement layer; And Ohmic contact layer disposed on the upper waveguide layer.

7. The quantum cascade laser according to claim 6, the active region includes: First active region disposed on the lower waveguide layer; And Second active region disposed on the first active region; Among them, the difference range of the quantum barrier strain values of the first active region and the second active region includes 0.05% to 0.1%, to limit the difference in peak gain between the first active region and the second active region.

8. The quantum cascade laser according to claim 7, the first active region includes 15 to 30 cascaded first active cores.

9. The quantum cascade laser according to claim 7, the second active region includes 15 to 30 cascaded second active cores.

10. The quantum cascade laser according to any one of claims 6 to 9 further includes two etched regions provided at intervals to divide the vertical structure formed by the active region, the optical confinement layer, the upper waveguide layer, and the ohmic contact layer into three regions; Among them, InP is filled in the two etched regions to confine the laser to lase in the middle region.

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