CN117039620A - Active region for quantum cascade laser and quantum cascade laser - Google Patents
Active region for quantum cascade laser and quantum cascade laser Download PDFInfo
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/3401—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers having no PN junction, e.g. unipolar lasers, intersubband lasers, quantum cascade lasers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34313—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer having only As as V-compound, e.g. AlGaAs, InGaAs
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Abstract
The present disclosure provides an active region for a quantum cascade laser and a quantum cascade laser, the active region including a plurality of cascaded periodic cascade structures, the periodic cascade structures including: a gain region, the gain region comprising: a plurality of gain quantum wells; a plurality of gain quantum barriers, wherein at least one gain quantum barrier is arranged between two adjacent gain quantum wells; the injection region is connected with the lowest gain quantum well; the thickness of the uppermost gain quantum well is the smallest, the thickness of the gain quantum well above the second gain quantum well is the largest, and the thicknesses of other gain quantum wells are sequentially reduced from top to bottom.
Description
Technical Field
The present disclosure relates to the field of laser technology, and more particularly, to an active region for a quantum cascade laser and a quantum cascade laser.
Background
The Quantum Cascade Laser (QCL) wavelength covers two atmospheric windows, has the advantages of small specific volume, portability and the like, and has important application in the fields of space communication, gas detection, medical diagnosis and the like.
In practical use, the threshold current density of the conventional quantum cascade laser is often high because of insufficient gain of each active core due to insufficient cascade cycle number of each active core. Devices with high threshold current densities often fail to achieve high electro-optic conversion efficiency and high output power. In addition, as the number of active cores increases, the difficulty of growth increases and the yield of devices decreases.
Disclosure of Invention
In view of the foregoing, embodiments of the present disclosure provide an active region for a quantum cascade laser and a quantum cascade laser.
An aspect of an embodiment of the present disclosure provides an active region for a quantum cascade laser, comprising:
a plurality of cascaded periodic cascade structures, said periodic cascade structures comprising:
a gain section, said gain section comprising:
a plurality of gain quantum wells;
a plurality of gain quantum barriers, wherein at least one gain quantum barrier is arranged between two adjacent gain quantum wells;
the injection region is connected with the lowest gain quantum well;
the thickness of the uppermost gain quantum well is the smallest, the thickness of the gain quantum well above the second gain quantum well is the largest, and the thicknesses of other gain quantum wells are sequentially reduced from top to bottom.
According to the embodiment of the disclosure, in the case that the number of the gain quantum wells is 4 and the number of the gain quantum barriers is 3, the thickness difference between the second gain quantum well and the third gain quantum well from top to bottom is smaller than the thickness difference between the third gain quantum well and the fourth gain quantum well.
According to embodiments of the present disclosure, the thickness of the lowermost gain quantum barrier is the largest, and the thicknesses of the other gain quantum barriers are the same or different.
According to an embodiment of the present disclosure, the implantation region includes:
a plurality of injection quantum barriers;
and the lowest injection quantum barrier is connected with the gain region of the periodic cascade structure of the next period.
According to an embodiment of the present disclosure, the thickness of the lowermost injection quantum barrier is the largest, the thickness of the second injection quantum barrier is the smallest, the thickness of the plurality of injection quantum barriers between the second injection quantum barrier and the lowermost injection quantum barrier increases sequentially from top to bottom, and the thickness of the first injection quantum barrier is greater than the thickness of the second injection quantum barrier and less than the thickness of the third injection quantum barrier.
According to an embodiment of the present disclosure, in the case where the number of the above-described injection quantum barriers is 5 and the number of the injection quantum wells is 4, the third injection quantum well and the fourth injection quantum barrier are doped layers of doped silicon.
Another aspect of an embodiment of the present disclosure provides a quantum cascade laser, comprising:
a substrate;
an active region as described above, disposed on a surface of the substrate;
a light confinement layer disposed on a side of the active region away from the substrate;
a metal electrode layer disposed on a side of the light confinement layer away from the active region;
and the back metal layer is arranged on one side of the substrate far away from the active area.
According to an embodiment of the present disclosure, the laser further includes:
and a plurality of waveguide layers, wherein at least one waveguide layer is disposed between the substrate and the active region and between the optical confinement layer and the metal motor layer.
According to an embodiment of the present disclosure, the active region includes a predetermined number of cascaded periodic cascade structures;
wherein, above-mentioned laser device still includes the antireflection coating.
According to an embodiment of the present disclosure, the laser further includes:
and the etching areas penetrate through the back metal layer, the light limiting layer and the active area and are partially positioned in the waveguide layer between the substrate and the active area, wherein filling materials are filled in the etching areas, and the etching areas are suitable for limiting laser to be excited in a laser among the etching areas.
According to the embodiment of the disclosure, the electron of the upper energy level of the laser has higher thermal activation energy by the special design of the thicknesses of the gain quantum wells and the gain quantum barriers, so that the thermal leakage of the electron of the upper energy level is reduced. Meanwhile, the lasing wavelength of the quantum cascade laser is determined by the energy level between sub-bands in a conduction band, and the energy level distance between the sub-bands can be changed by adjusting the thicknesses of a gain quantum well and a gain quantum barrier in a periodic cascade structure, so that the lasing wavelength of the quantum cascade laser is changed.
Drawings
The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments thereof with reference to the accompanying drawings in which:
fig. 1 schematically illustrates a schematic structure of an active region of one cycle according to an embodiment of the present disclosure;
FIG. 2 schematically illustrates an energy band structure schematic of an active region for one cycle in accordance with an embodiment of the present disclosure;
fig. 3 schematically illustrates a schematic structure of a quantum cascade laser according to an embodiment of the disclosure;
FIG. 4 schematically illustrates a schematic of active region XRD test results versus fitting results, in accordance with an embodiment of the disclosure;
FIG. 5 schematically illustrates an electroluminescent spectrum of an active region material according to an embodiment of the disclosure;
fig. 6 schematically illustrates a pulse tuning range diagram after a laser has composed a littrow external cavity laser with a blazed grating, according to an embodiment of the present disclosure.
Detailed Description
The present disclosure is described in further detail below with reference to the drawings and examples. It will be appreciated that the specific embodiments described herein are merely illustrative of the disclosure and are not limiting of the disclosure, as various features described in the embodiments may be combined to form multiple alternatives. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present disclosure are shown in the drawings.
Within the 8.6-9.6 μm band, C is present 2 H 4 、NH 3 And O 3 And the characteristic absorption peaks of various gases. In addition, the antisymmetric telescopic absorption peak of phosphate ion is located between 1100 and 1050cm -1 Within the range, the symmetrical telescopic absorption peak of nitrate ions is at 1050cm -1 Nearby, the anti-symmetric absorption peak of the ether bond is located at 1100cm -1 Nearby. It can be seen that a widely tuned laser in this band has great application prospects. QCL, because of its band structure specificity, often can exceed 100cm in its full width at half maximum of its practical gain spectrum -1 If the laser can realize wavelength mode selection by an external modulation mode, tunable single longitudinal mode laser output can be realized. An external cavity quantum cascade laser (EC-QCL) is a laser which is based on QCL and realizes mode selection of specific wavelength by means of blazed grating, and is successfully applied to the fields of mid-infrared gas detection, chemical detection, biological medicine detection and the like at present.
Compared with the medium-wave QCL, the energy band structure design of the long-wave QCL device has more constraint factors. First, the longer the wavelength, the smaller the interval between the energy levels in the microstrip, the more intense the non-radiative transition between the upper and lower energy levels of the laser, and in order to maintain the population inversion, the long-wave and very-long-wave lasers often use a design scheme of an active region of a oblique transition or a partial oblique transition, which can cause the transition matrix element corresponding to stimulated radiation to become smaller, so that the peak gain is insufficient. Meanwhile, the thermal backfill and the thermal leakage are further aggravated compared with the medium wave QCL due to the shortened inter-microstrip energy level interval. Second, free carrier absorption is proportional to wavelength, so the waveguide loss of the long wave QCL is greater. The long-wave QCL is still quite different from the medium-wave QCL in output power due to the influence of the above constraint factors. At present, the room temperature continuous wave working output power of the quantum cascade laser in the 4-5 μm wave band is already more than 5W, and the highest reported average power is only more than 2W for 8-10 μm.
The Bound-to-content (B-to-C) configuration is a common widely tuned active region design. Currently, the tuning range of the long-wave QCL based on the active area structure exceeds 100cm -1 . Another solution to achieve a widely tuned laser is a multi-core active area structure. Related researchers propose a multi-core active region structure with different components, and the pulse tuning range of an external cavity laser based on a secondary structure can cover 7.6-11.4 mu m. Other researchers provided a multi-core active region structure consisting of "compound wells" that achieved an external cavity tuning range of 5.2-11 μm. The multi-core active region structure has significant advantages in wide tuning, but the threshold current density tends to be high due to insufficient gain of each active core as a result of insufficient number of cascaded cycles of each active core. Devices with high threshold current densities often fail to achieve high electro-optic conversion efficiency and high output power. In addition, as the number of active cores increases, the difficulty of growth increases and the yield of devices decreases.
In view of this, the present disclosure provides an active region for a quantum cascade laser, the active region including a plurality of cascaded periodic cascade structures, the periodic cascade structures including: a gain region, the gain region comprising: a plurality of gain quantum wells; a plurality of gain quantum barriers, wherein at least one gain quantum barrier is arranged between two adjacent gain quantum wells; the injection region is connected with the lowest gain quantum well; the thickness of the uppermost gain quantum well is the smallest, the thickness of the gain quantum well above the second gain quantum well is the largest, and the thicknesses of other gain quantum wells are sequentially reduced from top to bottom.
Fig. 1 schematically illustrates a schematic structure of an active region for one cycle according to an embodiment of the present disclosure.
As shown in fig. 1, an active region 1000 for a quantum cascade laser 2000 includes:
a plurality of cascaded periodic cascade structures 100, the periodic cascade structures 100 comprising:
gain region 110, gain region 110 comprising:
a plurality of gain quantum wells 111;
a plurality of gain quantum barriers 112, wherein at least one gain quantum barrier 112 is disposed between two adjacent gain quantum wells 111;
an injection region 120 connected to the lowermost gain quantum well 111;
the thickness of the uppermost gain quantum well 111 is the smallest, the thickness of the next-to-upper gain quantum well 111 is the largest, and the thicknesses of the other gain quantum wells 111 decrease from top to bottom.
According to an embodiment of the present disclosure, gain quantum well 111 is In x Ga 1-x As, gain Quantum barrier 112 is In y Al 1-y As, wherein x is more than 0 and less than 1, and y is more than 0 and less than 1.
According to the embodiment of the present disclosure, electrons of upper energy level of laser light have higher thermal activation energy by the special design of the thicknesses of the plurality of gain quantum wells 111 and the plurality of gain quantum barriers 112, thereby reducing thermal leakage of electrons of upper energy level. Meanwhile, the lasing wavelength of the quantum cascade laser 2000 is determined by the energy level between sub-bands in the conduction band, and the energy level interval between sub-bands can be changed by adjusting the thicknesses of the gain quantum well 111 and the gain quantum barrier 112 in the periodic cascade structure 100, so that the lasing wavelength of the quantum cascade laser 2000 is changed.
According to an embodiment of the present disclosure, in the case where the number of gain quantum wells 111 is 4 and the number of gain quantum barriers 112 is 3, the thickness difference between the second gain quantum well 111 and the third gain quantum well 111 from top to bottom is smaller than the thickness difference between the third gain quantum well 111 and the fourth gain quantum well 111.
In one embodiment, referring to FIG. 1,4 gain quantum wells 111 are sequentially from top to bottom in thicknessAnd->
According to embodiments of the present disclosure, the thickness of the lowermost gain quantum barrier 112 is the largest, and the thicknesses of the other gain quantum barriers 112 are the same or different.
According to an embodiment of the present disclosure, the thicknesses of the 3 gain quantum barriers 112, referring to fig. 1, are in order from top to bottomAnd->
It should be noted that, the thicknesses described above and the thicknesses in fig. 1 may be adjusted according to actual requirements, and the examples described above are only used to illustrate the active region 1000 of the present disclosure, and the thicknesses of the gain quantum well 111 and the gain quantum barrier 112 of the present disclosure are not limited to the thicknesses described above.
According to an embodiment of the present disclosure, the implant region 120 includes:
a plurality of injection quantum barriers 121;
and a plurality of injection quantum wells 122, wherein at least one injection quantum well 122 is disposed between two adjacent injection quantum barriers 121, and the lowermost injection quantum barrier 121 is connected to the gain region 110 of the periodic cascade structure 100 of the next period.
According to an embodiment of the present disclosure, the injection quantum barrier 121 of the lower portion of the injection region 120 is connected with the gain quantum well 111 of the next period.
According to an embodiment of the present disclosure, the thickness of the lowermost injection quantum barrier 121 is the largest, the thickness of the second injection quantum barrier 121 is the smallest, the thickness of the plurality of injection quantum barriers 121 between the second injection quantum barrier 121 and the lowermost injection quantum barrier 121 increases sequentially from top to bottom, and the thickness of the first injection quantum barrier 121 is greater than the thickness of the second injection quantum barrier 121 and less than the thickness of the third injection quantum barrier 121.
According to embodiments of the present disclosure, multiple implant energy levels may exist within the implant region 120 through the special design of the implant region 120 to different implant quantum barrier 121 thicknesses. As the bias voltage is changed, electrons can be injected into the upper laser energy level at different injection energy levels, thereby facilitating a wide tuning range.
The energy level indicates an energy value of the microparticle system in each stable energy state.
According to an embodiment of the present disclosure, in the case where the number of the injection quantum barriers 121 is 5 and the number of the injection quantum wells 122 is 4, the third injection quantum well 122 and the fourth injection quantum barrier 121 are doped layers of doped silicon.
According to an embodiment of the present disclosure, the third injection quantum well 122 of the four injection quantum wells 122 and the fourth injection quantum barrier 121 of the five injection quantum barriers 121 are doped layers, and the doping concentration range includes 1.5×10 17 cm -3 -2.5×10 17 cm -3 The doping atom is Si. First, second, third, fourth, and fifth injection quantum barriers 121 each having a thickness ofAnd->First, second, third and fourth injection quantum wells 122 having a thickness of +.> And->
Fig. 2 schematically illustrates an energy band structure diagram of an active region for one cycle in accordance with an embodiment of the present disclosure.
One advantage of the active region 1000 of the present disclosure, in accordance with embodiments of the present disclosure, is that the spectrum may change significantly with changes in bias voltage. As shown in fig. 2 (a), at low bias (corresponding field strength of 44 kV/cm), the upper laser energy level is level 3, and the lower laser energy levels are level 1 and level 2. The transition element from level 3 to level 2 is 1.57nm, the corresponding wavelength is 10.5 μm, the transition element from level 3 to level 1 is 1nm, and the corresponding wavelength is 9.0 μm.
According to an embodiment of the present disclosure, peaks of both intensities can be seen on the electroluminescent spectrum with reference to fig. 5. As shown in fig. 2 (b), at high bias (corresponding field strength of 54.5 kV/cm), the upper laser energy level is level 7 and level 6, and the lower laser energy level is level 5. The transition element from level 7 to level 5 is 2nm, the corresponding wavelength is 9.5 μm, the transition element from level 6 to level 5 is 0.9nm, and the corresponding wavelength is 10.2 μm. The peaks of these two intensities can be seen from the electroluminescent spectrum of fig. 5. Another advantage of the active region 1000 is that electrons at the energy level of the laser have a high thermal activation energy. As shown in FIG. 2 (a), the energy level interval from the upper energy level 3 to the upper energy level 4 of the laser is 77meV under a bias corresponding to an electric field strength of 44 kV/cm. As shown in FIG. 2 (b), the energy levels of the upper laser energy levels 6 and 7 to the upper energy level 8 are 78meV and 70meV, respectively, under a bias corresponding to an electric field strength of 54.5 kV/cm. The advantage of this band structure is that the position of the gain can be modulated by biasing so that the spectrum can be concentrated at different wavelengths as desired.
Fig. 3 schematically illustrates a schematic structure of a quantum cascade laser according to an embodiment of the present disclosure.
As shown in fig. 3, the quantum cascade laser 2000 includes:
a substrate 2100;
an active region 1000 as described above, disposed on a surface of the substrate 2100;
a light confinement layer 2200 disposed on a side of the active region 1000 remote from the substrate 2100;
a metal electrode layer 2300 disposed on a side of the light-confining layer 2200 remote from the active region 1000;
a backside metal layer 2400 is disposed on a side of the substrate 2100 remote from the active region 1000.
According to embodiments of the present disclosure, the quantum cascade laser 2000 of the present disclosure may refer to a widely tuned quantum cascade laser 2000 having a center wavelength of 10.5 μm. The room temperature pulse tuning range can cover 10.11-10.57 mu m and 8.59-9.83 mu m at the same time, independent tuning of the two wave bands can be realized under different bias voltages, the total pulse tuning range can reach 1.7 mu m, and the structure of the active region 1000 is also beneficial to obtaining low threshold current density and high device yield.
According to an embodiment of the present disclosure, substrate 21002 is n-doped InP with a doping concentration range of 0.2×10 17 cm -3 ～5×10 17 cm -3 The thickness range includes 120 μm to 150 μm. The thickness of the active region 1000 ranges from 2.2 μm to 2.5 μm. For example, it may be 2.32. Mu.m.
In accordance with an embodiment of the present disclosure, the optical confinement layer 2200 is n-doped with a doping concentration of 2×10 16 cm -3 ～3.5×10 16 cm -3 The layer thickness is 0.2 μm to 0.5 μm.
According to an embodiment of the present disclosure, the metal electrode layer 2300 is n-doped InP with a doping concentration of 0.5×10 18 cm -3 ～5×10 18 cm -3 The layer thickness is 0.7 μm to 1 μm.
According to an embodiment of the present disclosure, the back metal layer 2400 is a germanium gold nickel alloy with a thickness of 0.3-0.6 μm.
Fig. 4 schematically illustrates a schematic of active region XRD test results versus fitting results, according to an embodiment of the disclosure.
According to an embodiment of the present disclosure, as shown in fig. 4, two complete sets of satellite peaks can be seen, and no significant broadening of the higher order satellite peaks appears, indicating a high repeatability of the structure of the active region 1000. The intensity and the position of the satellite peak in the test result are in good agreement with the theoretical fitting value, which shows that the composition and the thickness of the material are very close to the theoretical expectation.
According to the embodiment of the present disclosure, electrons of upper energy level of laser light have higher thermal activation energy by the special design of the thicknesses of the plurality of gain quantum wells 111 and the plurality of gain quantum barriers 112, thereby reducing thermal leakage of electrons of upper energy level. Meanwhile, the lasing wavelength of the quantum cascade laser 2000 is determined by the energy level between sub-bands in the conduction band, and the energy level interval between sub-bands can be changed by adjusting the thicknesses of the gain quantum well 111 and the gain quantum barrier 112 in the periodic cascade structure 100, so that the lasing wavelength of the quantum cascade laser 2000 is changed.
According to an embodiment of the present disclosure, the laser 2000 further includes:
a plurality of waveguide layers 2500, wherein at least one waveguide layer 2500 is disposed between the substrate 2100 and the active region 1000 and between the optical confinement layer 2200 and the metal electromechanical layer.
According to an embodiment of the present disclosure, the waveguide layer 2500 between the substrate 2100 and the active region 1000 is n-doped InP with a doping concentration of 2.8x10 16 cm -3 ～3.5×10 16 cm -3 The layer thickness is 3.2 μm to 3.6 μm. The waveguide layer 2500 between the optical confinement layer 2200 and the metal electromechanical layer is n-doped InP with a doping concentration range of 2.5×10 16 cm -3 ～4.5×10 16 cm -3 The thickness range includes 2.5 μm to 3.5 μm.
According to an embodiment of the present disclosure, the active region 1000 includes a preset number of cascaded periodic cascade structures 100; the laser 2000 further includes an antireflection film.
According to the embodiment of the disclosure, the preset number may be specifically set according to actual requirements, for example, may be 40-50.
According to an embodiment of the present disclosure, the laser 2000 further includes:
a plurality of etched regions 2600 disposed at intervals, the etched regions 2600 penetrating the back metal layer 2400, the optical confinement layer 2200, the active region 1000 and being partially located in the waveguide layer 2500 between the substrate 2100 and the active region 1000, wherein the etched regions 2600 are filled with a filler material, the etched regions 2600 being adapted to confine laser light from being excited within the laser 2000 between the plurality of etched regions 2600.
According to an embodiment of the present disclosure, the number of the etching regions 2600 may be 2, and a plurality of etching regions 2600 are disposed at intervals to divide a vertical structure of the active region 1000, the optical confinement layer 2200, the upper waveguide layer 2500, and the metal electrode layer 2300 into a plurality of regions; the etching regions 2600 are filled with a filling material to limit laser to the middle region for lasing and ensure a heat dissipation effect, wherein the filling material may be semi-insulating InP.
Fig. 5 schematically illustrates an electroluminescent spectrum of an active region material according to an embodiment of the present disclosure.
According to an embodiment of the present disclosure, the test sample used was a 2mm laser 2000 with a broken back facet and an anti-reflection film (Al 2O3/Ge,900nm/90 nm) on the front facet, the broken back facet was designed to attenuate the amplification and mode selection of the electroluminescent signal by the resonant cavity, so that a more realistic electroluminescent spectrum could be obtained, as shown in FIG. 5. At low field strengths (44 kV/cm), peak positions of the electroluminescent spectrum exist mainly at 950cm-1 and 1110cm-1, which approximately match the transition wavelength of energy level 3 to energy level 2 and the transition wavelength of energy level 3 to energy level 1 calculated by band theory in FIG. 2, respectively. At high field strengths (54.5 kV/cm), the peak positions of the electroluminescent spectrum exist mainly at 980cm-1 and 1060cm-1, which are matched with the transition wavelengths of energy level 6 to energy level 5 and energy level 7 to energy level 5 calculated by the energy band theory in FIG. 2, respectively.
Fig. 6 schematically illustrates a pulse tuning range diagram after a laser has composed a littrow external cavity laser with a blazed grating, according to an embodiment of the present disclosure.
According to embodiments of the present disclosure, the laser 2000 used has a cavity length of 2mm and an anti-reflection film (AR, al) on the front facet 2 O 3 Ge,900nm/90 nm), test duty cycle 5% and test pulse width 1. Mu.s. As shown in fig. 6, the abscissa represents the wave number (Wavelength), the left ordinate represents the normalized intensity (Normalized Intensity), and the right ordinate represents the output Power (Power). At low currents (1A), the range of external cavity modes can cover 10.20-10.68 μm, which approximately matches the band theory calculations at low biases, with the transition matrix element at low biases (44 kV/cm) being maximum at a transition wavelength of 10.5 μm. At high currents (1.8A), the range of external cavity modes can cover 8.59-9.67 μm, which approximately matches the band theory calculations at high biases, with the transition matrix element at high biases (54.5 kV/cm) being maximum at the transition wavelength of 9.5 μm.
The foregoing description of the preferred embodiments of the present disclosure is not intended to limit the disclosure, but rather to cover all modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present disclosure.
Claims (10)
1. An active region for a quantum cascade laser, comprising:
a plurality of cascaded periodic cascade structures, the periodic cascade structures comprising:
a gain region, the gain region comprising:
a plurality of gain quantum wells;
a plurality of gain quantum barriers, wherein at least one gain quantum barrier is arranged between two adjacent gain quantum wells;
the injection region is connected with the lowest gain quantum well;
the thickness of the uppermost gain quantum well is the smallest, the thickness of the gain quantum well above the second gain quantum well is the largest, and the thicknesses of other gain quantum wells are sequentially reduced from top to bottom.
2. The active region of claim 1, wherein, with the number of gain quantum wells being 4 and the number of gain quantum barriers being 3, a thickness difference between a second gain quantum well and a third gain quantum well from top to bottom is less than a thickness difference between a third gain quantum well and a fourth gain quantum well.
3. The active region of claim 1, wherein a thickness of a lowermost gain quantum barrier is greatest and thicknesses of other gain quantum barriers are the same or different.
4. The active region of any of claims 1-3, wherein the implant region comprises:
a plurality of injection quantum barriers;
and the lowest injection quantum barrier is connected with a gain region of a periodic cascade structure of the next period.
5. The active region of claim 4, wherein a thickness of a lowermost injection quantum barrier is greatest, a thickness of a second injection quantum barrier is smallest, a thickness of a plurality of injection quantum barriers between the second injection quantum barrier and the lowermost injection quantum barrier increases sequentially from top to bottom, and a thickness of the first injection quantum barrier is greater than a thickness of the second injection quantum barrier and less than a thickness of the third injection quantum barrier.
6. The active region of claim 4, wherein, in the case where the number of injection quantum barriers is 5 and the number of injection quantum wells is 4, the third injection quantum well and the fourth injection quantum barrier are doped layers of doped silicon.
7. A quantum cascade laser, comprising:
a substrate;
an active region as claimed in any one of claims 1 to 6, disposed on a surface of the substrate;
a light confinement layer disposed on a side of the active region remote from the substrate;
a metal electrode layer disposed on a side of the light confinement layer away from the active region;
and the back metal layer is arranged on one side of the substrate far away from the active region.
8. The laser of claim 7, further comprising:
and the waveguide layers are arranged between the substrate and the active area and between the light limiting layer and the metal motor layer.
9. The laser of claim 7, wherein the active region comprises a predetermined number of cascaded periodic cascade structures;
wherein, the laser also includes an antireflection film.
10. The laser of claim 8, further comprising:
the etching areas penetrate through the back metal layer, the light limiting layer and the active area and are partially located in the waveguide layer between the substrate and the active area, filling materials are filled in the etching areas, and the etching areas are suitable for limiting laser to be excited in a laser among the etching areas.
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