Quantum cascade laser and method of manufacturing the same

Abstract

This invention provides a quantum cascade laser and its fabrication method. The quantum cascade laser includes an active layer, which comprises multiple first sub-active layer units to the Mth sub-active layer units stacked sequentially in a first direction, where M is an integer greater than or equal to 2. Any mth sub-active layer unit includes W lower mth sub-active layers and W upper mth sub-active layers, with the lower mth sub-active layers and upper mth sub-active layers stacked alternately in the first direction, where m is an integer greater than or equal to 1 and less than or equal to M, and W is an integer greater than or equal to 2. Any mth sub-active layer unit with alternating stacked Q... m1 The m-th sub-active layer and Q m2 The m-th active layer contains doped ions; where Q m1 Q is an integer greater than or equal to 1 and less than W. m2 It is an integer greater than or equal to 1 and less than W; the doping concentration of the doped ion first increases and then decreases as the value of m increases.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to a quantum cascade laser and its fabrication method. Background Technology

[0002] The active layer of a quantum cascade laser (QCL) is typically composed of multiple cascaded active periods with identical structures. To simplify the epitaxial growth process and ensure consistency between periods, a uniform doping scheme is generally adopted for each period, meaning that the doping concentration of all periods (including the implanted and active regions) remains the same along the cascade direction. This uniform doping design was widely used in the early development of quantum cascade lasers, offering advantages such as simple fabrication, good structural repeatability, and a wide epitaxial growth window. Summary of the Invention

[0003] The technical problem addressed by this application is how to significantly improve the peak output power of quantum cascade lasers.

[0004] This application provides a quantum cascaded laser, including an active layer. The active layer comprises multiple first sub-active layer units to M-th sub-active layer units stacked sequentially in a first direction, where M is an integer greater than or equal to 2. Any m-th sub-active layer unit includes W lower m-th sub-active layers and W upper m-th sub-active layers, with the lower m-th sub-active layers and upper m-th sub-active layers alternately stacked in the first direction. Here, m is an integer greater than or equal to 1 and less than or equal to M, and W is an integer greater than or equal to 2. Any m-th sub-active layer unit with alternately stacked Q-type active layers in the first direction... m1 The m-th sub-active layer and Q m2 The m-th active layer contains doped ions; where Q m1 Q is an integer greater than or equal to 1 and less than W. m2 It is an integer greater than or equal to 1 and less than W; where the doping concentration of the doped ion first increases and then decreases as the value of m increases.

[0005] Optional, Among them, z m Let be the coordinates of the center position of the m-th sub-active layer unit in the first direction. Q in the m-th sub-active layer unit m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer Let be the coordinates of the center of the m-th sub-active layer unit with the highest doping concentration in the active layer, in the first direction. , , ,and It is a constant.

[0006] Optionally, the material of any m-th sub-active layer is In. x Ga (1-x) As, the material of any m-th sub-active layer is In. y Al (1-y) As.

[0007] Optional, Q m1 equals Q m2 Or, Q m1 and Q m2 The absolute value of the difference is equal to 1.

[0008] Optional, Q m1 Q is 1~2 m2 It is 1~2.

[0009] Optionally, the lower m-th sub-active layer with the largest thickness in the first direction among the W-th sub-active layers in any m-th sub-active layer unit has the doped ions; the upper m-th sub-active layer with the largest thickness in the first direction among the W-th sub-active layers in any m-th sub-active layer unit has the doped ions.

[0010] Optionally, in any m-th sub-active layer unit (WQ) m1 The m-th sub-active layer and (WQ) m1 The m-th active layer is an undoped layer.

[0011] Optionally, the thinnest of the W lower-m sub-active layers in any m-th sub-active layer unit has a first thickness in the first direction; wherein the first thickness decreases first and then increases as the value of m increases.

[0012] Optionally, when M is odd, the first thickness decreases as the value of m increases from 1 to (M+1) / 2, and increases as the value of m increases from (M+1) / 2 to M; when M is even, the first thickness decreases as the value of m increases from 1 to (M) / 2, and decreases as the value of m increases from (M / 2+1) to M.

[0013] Optionally, the thinnest of the W upper-m sub-active layers in any m-th sub-active layer unit has a second thickness in the first direction, wherein the second thickness first decreases and then increases as the value of m increases.

[0014] Optionally, when M is odd, the second thickness decreases as m increases from 1 to (M+1) / 2, and increases as m increases from (M+1) / 2 to M; when M is even, the second thickness decreases as m increases from 1 to (M) / 2, and decreases as m increases from (M / 2+1) to M.

[0015] Optionally, the temperature T(z) of the active layer in the first direction satisfies: Where a1, b1, and c1 are constants, z 01 z is a parameter related to temperature distribution. 01 Z represents the position of the active layer with the highest temperature in the first direction, and z represents the position coordinate of the active layer in the first direction. The m-th sub-active layer unit corresponding to the position of the active layer with the highest temperature in the first direction is the same as the m-th sub-active layer unit with the highest doping concentration in the active layer.

[0016] This application also provides a method for fabricating a quantum cascade laser, comprising: forming an active layer; wherein forming the active layer comprises: forming a plurality of first sub-active layer units to Mth sub-active layer units stacked sequentially in a first direction, where M is an integer greater than or equal to 2, any mth sub-active layer unit comprising W mth lower sub-active layers and W mth upper sub-active layers, the mth lower sub-active layers and the mth upper sub-active layers being alternately stacked in the first direction, where m is an integer greater than or equal to 1 and less than or equal to M, and W is an integer greater than or equal to 2; in any mth sub-active layer unit, Q... m1 The m-th sub-active layer and Q m2 Doping is performed on the m-th active layer, where the doping concentration of the dopant ions first increases and then decreases with the increase of the value of m, where Q m1 Q is an integer greater than or equal to 1 and less than W. m2 It is an integer greater than or equal to 1 and less than W.

[0017] Optionally, Q-type elements are alternately stacked in the first direction in any m-th sub-active layer unit. m1 The m-th sub-active layer and Q m2 Doping is performed in the m-th active layer, including: according to In any m-th sub-active layer unit, Q-type elements are alternately stacked in the first direction. m1 The m-th sub-active layer and Q m2 Doping is performed in the m-th active layer; where z m Let be the coordinates of the center position of the m-th sub-active layer unit in the first direction. Q in the m-th sub-active layer unit m1 The m-th sub-active layer and Qm2 The doping concentration of the m-th active layer Let be the coordinates of the center of the m-th sub-active layer unit with the highest doping concentration in the active layer, located in the first direction. , , ,and It is a constant.

[0018] Optional, Q m1 Q is 1~2 m2 It is 1~2.

[0019] Optionally, in any m-th sub-active layer unit, at least the m-th lower sub-active layer with the largest thickness in the first direction among the m-th lower sub-active layers of the W layer is doped; in any m-th sub-active layer unit, at least the m-th upper sub-active layer with the largest thickness in the first direction among the m-th upper sub-active layers of the W layer is doped.

[0020] Optionally, the thinnest of the W lower-m sub-active layers in any m-th sub-active layer unit has a first thickness in the first direction; wherein the first thickness decreases first and then increases as the value of m increases.

[0021] Optionally, the thinnest of the W upper-m sub-active layers in any m-th sub-active layer unit has a second thickness in the first direction, wherein the second thickness first decreases and then increases as the value of m increases.

[0022] Optionally, the preparation method further includes: before doping, obtaining the temperature T(z) distribution of the active layer in the first direction, wherein T(z) satisfies: Where a1, b1, and c1 are constants, z 01 z is a parameter related to temperature distribution. 01 Let z be the position of the active layer with the highest temperature in the first direction, and z be the position coordinate of the active layer in the first direction; the center position of the m-th sub-active layer unit corresponding to the position of the active layer with the highest temperature in the first direction is taken as... The value of .

[0023] The technical solution of this invention has the following beneficial effects: The quantum cascade laser provided by this invention utilizes the tunable characteristic of the switching current caused by the doping concentration of different sub-active layer units in the active layer to compensate for the influence of the temperature gradient on the switching current in the active layer. The doping concentration in the central region of the active layer along the first direction is higher than that in the edge region along the first direction. By performing specific non-uniform doping design in different sub-active layer units in the active layer, the local switching current of each sub-active layer unit is synchronized or highly synchronized under the same global injection current density. That is, most or all of the sub-active layer units can simultaneously reach or approach their maximum power contribution point under the same current conditions, significantly improving the peak output power of the quantum cascade laser and enhancing its performance. This scheme not only significantly improves the overall peak output power, wall insertion efficiency, and high-temperature continuous wave performance of the quantum cascade laser, but also has quantitative designability based on the fitted linear relationship. It facilitates precise optimization of the doping distribution through thermal simulation combined with the doping-switching current relationship curve, while maintaining the compatibility and feasibility of the epitaxial growth process. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a quantum cascade laser according to an embodiment of this application; Figure 2 for Figure 1 A schematic diagram of the active layer; Figure 3 This is a schematic diagram showing how the temperature of the active layer changes with the position of the active layer in the first direction. Figure 4 Power-operating current curves and operating voltage-operating current curves for different quantum cascade lasers in related technologies; Figure 5 The curves show the variation of the doping concentration of the active layer of different quantum cascade lasers in related technologies with the operating current corresponding to the current inversion point; Figure 6 The power-operating current curves and operating voltage-operating current curves of quantum cascade lasers in related technologies under different ambient temperatures are shown. Figure 7 This is a curve showing the change in operating current at the highest temperature point along the first direction of the active layer of a quantum cascade laser under different ambient temperatures in related technologies, corresponding to the temperature and current reversal point. Figure 8 Q is the m-th sub-active layer cell of the active layer in this application. m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer The curve showing the change in the center position of the m-th sub-active layer unit in the first direction Z; Figure 9 The electric field intensity of the quantum cascade laser in Test Example 1 varies with the doping concentration of the active layer in the first direction; Figure 10 This is a schematic diagram showing the change of the center wavelength of the quantum cascaded laser in Test Example 1 as a function of the electric field intensity. Figure 11 The power-operating current curves and operating voltage-operating current curves of the quantum cascade lasers for comparison and test example 1 are shown. Figure 12 The normalized light intensity versus wavelength curves of the quantum cascaded lasers in Test Example 1 and Test Example 2 are shown. Figure 13 The power-operating current curves and operating voltage-operating current curves of the quantum cascade lasers in Test Example 1 and Test Example 2 are shown. Detailed Implementation

[0026] Research has revealed that quantum cascade lasers, including those with uniformly doped active layers, have significant technical drawbacks under high-power continuous wave or high duty cycle operating conditions. Because the active layer of a quantum cascade laser exhibits a significant axial temperature gradient along its growth direction, the current reversal point corresponding to power reduction strongly depends on local temperature and local doping levels. Under uniform doping conditions, with identical doping in each period, the theoretical reversal point current density is essentially the same for each period. However, due to the influence of the temperature gradient, the actual reversal behavior differs significantly: the reversal point of high-temperature periods occurs earlier, resulting in shorter quantum cascade laser level lifetimes, decreased injection efficiency, and enhanced thermal scattering; while the reversal point of low-temperature periods is relatively delayed. Therefore, under the same global injection current, it is impossible for all periods to simultaneously operate at their optimal state or reach their current reversal point simultaneously. Specifically, when the current increases to the point where the period at the low temperature position approaches its maximum power contribution, the period at the high temperature position has already entered a severe reversal region, with a significant decrease in gain and even parasitic losses; conversely, when the current is adapted to the period at the high temperature position, the period at the low temperature position has not yet fully realized its potential. Ultimately, this leads to a peak power in the overall power-current curve that is significantly lower than the theoretical value under ideal uniform temperature conditions, limiting the maximum output power, wall insertion efficiency, and high-temperature continuous wave performance of the quantum cascade laser.

[0027] Through arduous practice, a technical solution has been developed to address the problem of peak power reduction caused by asynchronous flipping points of individual active layers due to temperature gradients in the uniformly doped active layers of existing quantum cascade lasers. By optimizing the doping distribution of the active layers, the electro-thermal-optical characteristics of each cycle are better matched under the operating current. This allows most or all of the active layer units to simultaneously reach or approach their maximum power contribution points near the same global current, even in the presence of temperature gradients, significantly improving the peak output power and overall performance of the quantum cascade laser.

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] One embodiment of the present invention provides a quantum cascade laser, with reference to... Figure 1 and Figure 2 The active layer 130 includes a plurality of first sub-active layer units 1301 to Mth sub-active layer units stacked sequentially in the first direction Z, where M is an integer greater than or equal to 2. Any mth sub-active layer unit includes W mth lower sub-active layers and W mth upper sub-active layers. The mth lower sub-active layers and mth upper sub-active layers are stacked alternately in the first direction Z, where m is an integer greater than or equal to 1 and less than or equal to M, and W is an integer greater than or equal to 2.

[0032] In any m-th sub-active layer unit, Q cells are alternately stacked in the first direction Z. m1 The m-th sub-active layer and Q m2 The m-th active layer contains doped ions. Where, Q m1 Q is an integer greater than or equal to 1 and less than W.m2 It is an integer greater than or equal to 1 and less than W; where the doping concentration of the doped ion first increases and then decreases as the value of m increases.

[0033] The quantum cascade laser provided in this embodiment utilizes the tunable characteristic of the switching current caused by the doping concentration of different sub-active layer units in the active layer 130 to compensate for the influence of the temperature gradient on the switching current in the active layer 130. The doping concentration in the central region of the active layer 130 along the first direction Z is higher than the doping concentration in the edge region of the active layer along the first direction Z. Through specific non-uniform doping design in different sub-active layer units in the active layer 130, the local switching current of each sub-active layer unit is synchronized or highly synchronized under the same global injection current density. That is, most or all of the sub-active layer units can simultaneously reach or approach their maximum power contribution point under the same current conditions, significantly improving the peak output power of the quantum cascade laser and enhancing its performance. This scheme not only significantly improves the overall peak output power, wall insertion efficiency, and high-temperature continuous wave performance of the quantum cascade laser, but also has quantitative designability based on the fitted linear relationship. It is convenient to accurately optimize the doping distribution through thermal simulation combined with the doping-switching current relationship curve, while maintaining the compatibility and feasibility of the epitaxial growth process.

[0034] In some embodiments, reference Figure 1 The quantum cascade laser also includes an upper confinement layer 150 and an upper waveguide layer 140, a lower confinement layer 110 and a lower waveguide layer 120. The quantum cascade laser also includes a substrate layer 100. The lower waveguide layer 120 is located on the side of the lower confinement layer 110 opposite to the substrate layer 100. The active layer 130 is located on the side of the lower waveguide layer 120 opposite to the lower confinement layer 110. The upper waveguide layer 140 is located on the side of the active layer 130 opposite to the lower waveguide layer 120. The upper confinement layer 150 is located on the side of the upper waveguide layer 140 opposite to the active layer 130.

[0035] In some embodiments, reference Figure 1 The quantum cascade laser also includes a contact layer 160 located on the side of the upper confinement layer 150 opposite to the active layer 130. The quantum cascade laser also includes a first electrode layer 170 and a second electrode layer 180. The first electrode layer 170 is located on the side of the contact layer 160 along a first direction Z opposite to the upper confinement layer 150. The second electrode layer 180 is located on the side of the substrate layer 100 opposite to the lower confinement layer 110. The quantum cascade laser also includes a heat sink 200 located on the side of the second electrode layer 180 opposite to the substrate layer 100.

[0036] The band gaps of the m-th lower active layer and the m-th upper active layer are different.

[0037] In some embodiments, the material of any m-th lower sub-active layer is In. xGa (1-x) As, the material of any m-th sub-active layer is In. y Al (1-y) As.

[0038] In other embodiments, the materials of the m-th lower active layer and the m-th upper active layer are not limited.

[0039] In some embodiments, the active layer 130 includes a plurality of first sub-active layer units 1301 to Mth sub-active layer units stacked sequentially in a first direction Z. M can be 30 to 50.

[0040] In some embodiments, any m-th sub-active layer unit includes W m-th lower sub-active layers and W m-th upper sub-active layers, where W is 5 to 12 and 2W is 10 to 24.

[0041] In some embodiments, M equals 4 as an example, W equals 8 as an example, and Q equals... m2 Equal to 1, Q m1 Using 1 as an example, the active layer 130 includes multiple first sub-active layer units 1301, second sub-active layer units 1302, third sub-active layer units 1303, and fourth sub-active layer units 1304 stacked sequentially in the first direction Z. The first sub-active layer unit 1301 includes eight first lower sub-active layers and eight first upper sub-active layers, which are alternately stacked in the first direction Z. The second sub-active layer unit 1302 includes eight second lower sub-active layers and eight second upper sub-active layers, which are alternately stacked in the first direction Z. The third sub-active layer unit 1303 includes eight third lower sub-active layers and eight third upper sub-active layers, which are alternately stacked in the first direction Z. The fourth sub-active layer unit 1304 includes eight fourth lower sub-active layers and eight fourth upper sub-active layers, which are alternately stacked in the first direction Z. Specifically, in the first sub-active layer unit 1301, one first lower active layer and one first upper sub-active layer stacked in the first direction Z contain doped ions; in the second sub-active layer unit 1302, one second lower sub-active layer and one second upper sub-active layer stacked in the first direction Z contain doped ions; in the third sub-active layer unit 1303, one third lower sub-active layer and one third upper sub-active layer stacked in the first direction Z contain doped ions; and in the fourth sub-active layer unit 1304, one fourth lower sub-active layer and one fourth upper sub-active layer stacked in the first direction Z contain doped ions. The doping concentration of the doped ions first increases and then decreases with increasing value of m.

[0042] In other embodiments, the value of M is not restricted, the value of W is not restricted, and the value of Q is...m2 and Q m1 There are no restrictions on the value of .

[0043] In some embodiments, Among them, z m Let be the coordinates of the center position of the m-th sub-active layer element in the first direction Z. Q in the m-th sub-active layer unit m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer Let Z be the coordinate of the center of the m-th sub-active layer unit with the highest doping concentration in the active layer 130, in the first direction Z. , , ,and It is a constant.

[0044] In some embodiments, in any m-th sub-active layer unit (WQ) m1 The m-th sub-active layer and (WQ) m1 The m-th upper sub-sub active layer is undoped. Doping is performed only in a portion of the m-th lower sub-sub active layer and a portion of the m-th upper sub-sub active layer to achieve precise control of charge carriers. Simultaneously, in (WQ) m1 The m-th sub-active layer and (WQ) m1 The m-th active layer is not doped, which reduces the absorption loss of the optical field by the dopant ions.

[0045] In some embodiments, Q m1 equals Q m2 Or, Q m1 and Q m2 The absolute value of the difference is equal to 1.

[0046] In some embodiments, Q m1 Q is 1~2 m2 The number is 1~2. In any m-th sub-active layer unit, the number of doped lower m-th sub-active layers and the number of doped upper m-th sub-active layers are both relatively small, which further reduces the absorption loss of the optical field by the dopant ions.

[0047] In some embodiments, the lower m-th sub-active layer with the largest thickness in the first direction Z of the W-layer in any m-th sub-active layer unit has doped ions; the upper m-th sub-active layer with the largest thickness in the first direction Z of the W-layer in any m-th sub-active layer unit also has doped ions. Since the number of electron tunneling and transitions is relatively large in the lower m-th sub-active layer with the largest thickness in the first direction Z of the W-layer and the upper m-th sub-active layer with the largest thickness in the first direction Z of the W-layer in any m-th sub-active layer unit, doping ions in the lower m-th sub-active layer and the upper m-th sub-active layer at least at these positions can better adjust the carrier density in the m-th sub-active layer unit.

[0048] In some embodiments, the temperature T(z) of the active layer 130 in the first direction Z satisfies: Where, a1, b1, and c1 are constants, z 01 z is a parameter related to temperature distribution. 01 Z represents the position of the active layer 130 with the highest temperature in the first direction Z, where z is the position coordinate of the active layer 130 in the first direction Z. The m-th sub-active layer unit corresponding to the position of the active layer 130 with the highest temperature in the first direction Z is the same as the m-th sub-active layer unit with the highest doping concentration in the active layer 130.

[0049] Since the heat generated by the active layer 130 of the quantum cascade laser is mainly conducted through the heat sink 200 below, the temperature T(z) of the active layer 130 has a certain asymmetry in the distribution along the first direction Z.

[0050] refer to Figure 3 The temperature of the active layer 130 of the quantum cascade laser first increases and then decreases in the first direction Z. That is, the temperature of the active layer 130 in the central region of the first direction Z is greater than the temperature of the active layer 130 in the edge region of the first direction Z. Figure 3 The horizontal axis represents the position coordinates of the quantum cascade laser in the first direction Z, in micrometers. Figure 3 The vertical axis represents temperature, with units of Kelvin (K).

[0051] Figure 4 The figures show the power-operating current curves and operating voltage-operating current curves of different quantum cascade lasers in related technologies. The active layer in different quantum cascade lasers has different doping concentrations, while the active layer in the same quantum cascade laser is uniformly doped. Figure 4Different colored curves correspond to different quantum cascade lasers. Specifically, one quantum cascade laser has an active layer with a first doping concentration, another has an active layer with a second doping concentration, and yet another has an active layer with a third doping concentration. The ambient temperature of the active layers of all three quantum cascade lasers is set to be the same. Power-current and voltage-current curves for different quantum cascade lasers are obtained. The third doping concentration is greater than the second doping concentration, and the second doping concentration is greater than the first doping concentration. It can be seen that as the doping concentration increases, the operating current value at the current inversion point corresponding to the decrease in power increases. Figure 4 The horizontal axis represents the operating current of the quantum cascade laser, measured in amperes. Figure 4 The vertical axis on the left represents the operating voltage of the quantum cascade laser, measured in volts. Figure 4 The vertical axis on the right represents the power of the quantum cascade laser, measured in watts. Power is the product of the operating voltage and the operating current.

[0052] Figure 5 The curves show the variation of the doping concentration of the active layer of different quantum cascade lasers with the operating current corresponding to the current inversion point. The active layers in different quantum cascade lasers have different doping concentrations, while the active layers in the same quantum cascade laser are uniformly doped. Figure 5 The horizontal axis represents the doping concentration of the active layer, in units of 10. 16 atom / cm 3 . Figure 5 The vertical axis represents the operating current at the current inversion point, measured in amperes. For the active layer of different quantum cascade lasers, the operating current at the current inversion point increases with increasing doping concentration. Furthermore, the operating current at the current inversion point exhibits an approximately positive correlation with the doping concentration. The operating current at the current inversion point is simply the inversion current.

[0053] Figure 6 This paper presents the power-operating current and operating voltage-operating current curves of a quantum cascade laser in related technologies under different ambient temperatures. The active layer in the quantum cascade laser is uniformly doped. As the ambient temperature increases, the operating current corresponding to the current inversion point decreases as the power decreases. Figure 6 The horizontal axis represents the operating current of the quantum cascade laser, measured in amperes. Figure 6 The vertical axis on the left represents the operating voltage of the quantum cascade laser, measured in volts. Figure 6 The vertical axis on the right represents the power of the quantum cascade laser, measured in watts. Power is the product of operating current and operating voltage.

[0054] Figure 7This is a curve showing the change in operating current at the temperature and current reversal point of the active layer along the first direction in a quantum cascade laser under different ambient temperatures. The active layer in the quantum cascade laser is uniformly doped, and the temperature of the active layer at the temperature of the highest point in the first direction has a fixed difference from the ambient temperature. Figure 7 The horizontal axis represents the temperature at the point of highest temperature along the first direction of the active layer, in Kelvin. Figure 7 The vertical axis represents the operating current corresponding to the current reversal point, measured in amperes. As the temperature at the highest point along the first direction of the active layer increases, the operating current corresponding to the current reversal point decreases. Furthermore, the operating current at the current reversal point exhibits an approximately negative correlation with the temperature at the highest point along the first direction of the active layer. When the temperature at the highest point along the first direction of the active layer increases, it accelerates the nonradiative relaxation process of the upper laser level in the active layer, shortens the upper level lifetime, and leads to a decrease in gain coefficient and injection efficiency. Simultaneously, high temperatures enhance backscattering and electron leakage, further promoting the emergence of negative differential conductance, thus causing the active layer of the quantum cascade laser to reach the current reversal point earlier. When the active layer has a low level of uniform doping, free carrier absorption and Joule heating are relatively weak, and the temperature effect becomes the dominant factor. Therefore, the operating current corresponding to the current reversal point exhibits a highly sensitive linear dependence on the temperature at the highest point along the first direction of the active layer. This further confirms the limiting effect of temperature gradient on the performance of quantum cascade lasers in the uniform doping design of the active layer in the relevant technology: due to the non-uniform temperature distribution of the active layer along the epitaxial direction (first direction), the operating current corresponding to the current reversal point of different sub-active layer groups is different, which ultimately makes it impossible for the quantum cascade laser to achieve synchronous optimal operation of all sub-active layer groups at a single current point, and the peak power of the quantum cascade laser is significantly suppressed.

[0055] Figure 8 In this application, Q is the m-th sub-active layer cell of active layer 130. m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer The curve showing the change in the center position of the m-th sub-active layer unit in the first direction Z. Figure 8 The horizontal axis represents the position of the active layer 130 in the first direction Z, in micrometers. Figure 8 The vertical axis represents the Q value in the m-th sub-active layer unit of active layer 130. m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer. This application, . Figure 8 doping concentration This represents the dimensionless, normalized doping concentration.

[0056] In this application, the adjustable doping concentration of different sub-active layer units in the active layer 130 on the switching current is utilized to compensate for the influence of the temperature gradient in the active layer 130 on the switching current. The doping concentration in the central region of the active layer 130 along the first direction Z is higher than the doping concentration in the edge region of the active layer 130 along the first direction Z. Through a specific non-uniform doping design in the different sub-active layer units of the active layer 130, the local switching current of each sub-active layer unit is synchronized or highly synchronized under the same global injection current density. That is, most or all of the sub-active layer groups can simultaneously reach or approach their maximum power contribution point under the same current conditions, significantly improving the peak output power of the quantum cascade laser and enhancing its performance.

[0057] like Figure 9 The dimensions of the first to Mth sub-active layer units are designed to be consistent in the first direction. Under the same current density, the higher the doping concentration of the sub-active layer units in a single cycle, the lower the bias voltage exhibited by the sub-active layer units in a single cycle; that is, the sub-active layer units in a single cycle bear a lower bias voltage. A higher doping concentration increases the carrier density of a single cycle of the active layer, and a lower bias voltage is required to maintain the required current level while ensuring that the transport rate remains unchanged. Figure 9 The horizontal axis represents the doping concentration of the active layer in the first direction, in units of 10. 16 atom / cm 3 . Figure 9 The vertical axis represents the electric field strength, measured in kilovolts per centimeter. The thickness of a single-cycle sub-active layer unit in the first direction is fixed, and the dimensions of the first to Mth sub-active layer units are the same in the first direction. Therefore, a greater electric field strength means a greater bias voltage.

[0058] like Figure 10 , Figure 10 The horizontal axis represents the electric field strength, measured in kilovolts per centimeter. Figure 10 The vertical axis represents the center wavelength of the light emitted by the quantum cascade laser, measured in micrometers. For example... Figure 10 The simulation results show that the band structure of the active layer of the quantum cascade laser undergoes corresponding modulation changes with the applied electric field under different bias voltages. As the bias voltage gradually increases, the energy level spacing between the upper and lower laser levels in the active layer increases accordingly, leading to an increase in the energy required for radiative transitions. Based on the correlation between energy and center wavelength, this change causes a slight blue shift in the center wavelength of the quantum cascade laser. These phenomena indicate that by adjusting the applied bias voltage, the center wavelength of the quantum cascade laser emission can be effectively controlled within a certain range.

[0059] Based on the simulation analysis results above, it can be concluded that the structural design of the periodicity of the active layer of a quantum cascade laser needs to be coordinated and comprehensively considered with the center wavelength of the target emission. In the periodicity of the active layer with a high doping concentration, due to the high carrier density inside the active layer, the sensitivity of the active layer to the applied voltage bias is relatively low under the same injection current conditions. This results in a significant reduction in the blue shift amplitude of the center wavelength of the quantum cascade laser caused by the change in bias.

[0060] Based on the above characteristics, when designing with a high-doped active layer periodicity, the center wavelength of the quantum cascade laser can be pre-designed to be in a relatively shorter band, thereby suppressing the emission wavelength bandwidth of the quantum cascade laser. At the same current inversion point, this effectively compensates for the wavelength drift of the quantum cascade laser under the actual bias voltage, reducing the emission spectral bandwidth and enabling the quantum cascade laser to achieve better power and spectral output performance in operation. In some embodiments, the thinnest of the W lower m-th sub-active layers in any m-th sub-active layer unit has a first thickness in a first direction; wherein the first thickness decreases first and then increases with the value of m. The thinnest of the W upper m-th sub-active layers in any m-th sub-active layer unit has a second thickness in a first direction, wherein the second thickness decreases first and then increases with the value of m. By designing the size difference of the lower m-th sub-active layer in the first direction and the size difference of the upper m-th sub-active layer in the first direction in different sub-active layer units, the wavelength drift of the quantum cascade laser under the actual bias voltage is compensated, and the emission spectrum bandwidth is reduced.

[0061] For example, the active layer 130 includes multiple first sub-active layer units 1301 to Mth sub-active layer units stacked sequentially in the first direction Z. The first thickness decreases and then increases as the value of m increases, and the second thickness decreases and then increases as the value of m increases. When M is odd, the first thickness decreases as the value of m increases from 1 to (M+1) / 2, and increases as the value of m increases from (M+1) / 2 to M. When M is even, the first thickness increases as the value of m increases from 1 to (M) / 2. The thickness decreases as the value of m increases. When m ranges from (M / 2+1) to M, the first thickness decreases as the value of m increases. When M is odd, when m ranges from 1 to (M+1) / 2, the second thickness decreases as the value of m increases. When m ranges from (M+1) / 2 to M, the second thickness increases as the value of m increases. When M is even, when m ranges from 1 to (M) / 2, the second thickness decreases as the value of m increases. When m ranges from (M / 2+1) to M, the second thickness decreases as the value of m increases.

[0062] Comparative Example: The active layer in a quantum cascade laser comprises multiple sub-active layer groups alternately stacked in a first direction. Each sub-active layer group includes a first sub-active layer unit to an Mth sub-active layer unit stacked sequentially in the first direction; M is an integer greater than or equal to 2; the active layers are uniformly doped in the first direction. Any mth sub-active layer unit comprises a lower mth sub-active layer and an upper mth sub-active layer alternately stacked in the first direction. The dimensions of the first to Mth sub-active layer units are identical in the first direction. The doping concentration of the first to Mth sub-active layer units is identical in the first direction.

[0063] Test Example 1: The active layer in a quantum cascade laser comprises multiple sub-active layer groups that are alternately stacked in a first direction. Each sub-active layer group comprises a first sub-active layer unit to the Mth sub-active layer unit stacked sequentially in the first direction; M is an integer greater than or equal to 2. Any mth sub-active layer unit comprises a lower mth sub-active layer and an upper mth sub-active layer that are alternately stacked in the first direction. Q in the mth sub-active layer unit... m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer satisfy, The dimensions of the first sub-active layer unit to the Mth sub-active layer unit are the same in the first direction.

[0064] Test Example 2: The active layer in a quantum cascade laser comprises multiple sub-active layer groups that are alternately stacked in a first direction. Each sub-active layer group comprises a first sub-active layer unit to the Mth sub-active layer unit stacked sequentially in the first direction; M is an integer greater than or equal to 2. Any mth sub-active layer unit comprises a lower mth sub-active layer and an upper mth sub-active layer that are alternately stacked in the first direction. Q in the mth sub-active layer unit... m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer satisfy, In any m-th sub-active layer unit, the thinnest m-th lower sub-active layer among multiple m-th sub-active layers has a first thickness in a first direction; wherein, the first thickness first decreases and then increases as the value of m increases. In any m-th sub-active layer unit, the thinnest m-th upper sub-active layer among multiple m-th upper sub-active layers has a second thickness in a first direction; wherein, the second thickness first decreases and then increases as the value of m increases.

[0065] Figure 11The power-operating current curves and operating voltage-operating current curves of the quantum cascade lasers in Comparative Example and Test Example 1 are shown. In the quantum cascade laser of this application, the active layer is non-uniformly doped in the first direction Z, which can increase the switching current, thereby improving the power and power efficiency of the quantum cascade laser. Figure 11 The horizontal axis represents the operating current of the quantum cascade laser, measured in amperes. Figure 11 The vertical axis on the left represents the operating voltage of the quantum cascade laser, measured in volts. Figure 11 The vertical axis on the right represents the power emitted by the quantum cascade laser, measured in watts.

[0066] Figure 12 The normalized light intensity versus wavelength curves are shown for the quantum cascade lasers in Test Example 1 and Test Example 2. Figure 13 The power-current and operating voltage-current curves for the quantum cascade lasers in Test Example 1 and Test Example 2 are shown. Compared to Test Example 1, Test Example 2 can further reduce the full width at half maximum (FWHM) of the spectral gain, increase the peak material gain, thereby reducing the threshold current density and improving the power efficiency of the quantum cascade laser. Figure 12 The horizontal axis represents wavelength, with units in micrometers. Figure 12 The vertical axis represents the normalized light intensity of the quantum cascade laser. Figure 13 The horizontal axis represents the operating current of the quantum cascade laser, measured in amperes. Figure 13 The vertical axis on the left represents the operating voltage of the quantum cascade laser, measured in volts. Figure 13 The vertical axis on the right represents the power emitted by the quantum cascade laser, measured in watts.

[0067] This application also provides a method for fabricating a quantum cascade laser, comprising: forming an active layer 130; wherein, forming the active layer 130 comprises: forming a plurality of first sub-active layer units to the Mth sub-active layer units stacked sequentially in a first direction, where M is an integer greater than or equal to 2, any mth sub-active layer unit comprising W mth lower sub-active layers and W mth upper sub-active layers, the mth lower sub-active layers and the mth upper sub-active layers being alternately stacked in the first direction, where m is an integer greater than or equal to 1 and less than or equal to M; W is an integer greater than or equal to 2; and in any mth sub-active layer unit, Q... m1 The m-th sub-active layer and Q m2 Doping is performed on the m-th active layer, where the doping concentration of the dopant ions first increases and then decreases with the increase of the value of m, where Q m1 Q is an integer greater than or equal to 1 and less than W. m2 It is an integer greater than or equal to 1 and less than W.

[0068] In any m-th sub-active layer unit, Q is alternately stacked in the first direction. m1 The m-th sub-active layer and Q m2 Doping is performed in the m-th active layer, including: according to In any m-th sub-active layer unit, Q-type elements are alternately stacked in the first direction. m1 The m-th sub-active layer and Q m2 Doping is performed in the m-th active layer; where z m Let be the coordinates of the center position of the m-th sub-active layer unit in the first direction. Q in the m-th sub-active layer unit m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer Let be the coordinates of the center of the m-th sub-active layer unit with the highest doping concentration in the active layer, in the first direction. , , ,and It is a constant.

[0069] The fabrication method of the quantum cascade laser further includes: obtaining the temperature T(z) distribution of the active layer in the first direction before doping, wherein T(z) satisfies: Where a1, b1, and c1 are constants, z 01 z is a parameter related to temperature distribution. 01 Let z be the position of the active layer with the highest temperature in the first direction, and z be the position coordinate of the active layer in the first direction; the center position of the m-th sub-active layer unit corresponding to the position of the active layer with the highest temperature in the first direction is taken as... The value of .

[0070] The band gaps of the m-th lower active layer and the m-th upper active layer are different. In some embodiments, the material of any m-th lower active layer is In. x Ga (1-x) As, the material of any m-th sub-active layer is In. y Al (1-y) As.

[0071] In some embodiments, Q m1 equals Q m2 Or, Q m1 and Q m2 The absolute value of the difference is equal to 1.

[0072] In some embodiments, in any m-th sub-active layer unit (WQ) m1 The m-th sub-active layer and (WQ) m1The m-th upper sub-sub active layer is undoped. Doping is performed only in a portion of the m-th lower sub-sub active layer and a portion of the m-th upper sub-sub active layer to achieve precise control of charge carriers. Simultaneously, in (WQ) m1 The m-th sub-active layer and (WQ) m1 The m-th active layer is not doped, which reduces the absorption loss of the optical field by the dopant ions.

[0073] In some embodiments, Q m1 Q is 1~2 m2 The number is 1~2. In any m-th sub-active layer unit, the number of doped lower m-th sub-active layers and the number of doped upper m-th sub-active layers are both relatively small, which further reduces the absorption loss of the optical field by the dopant ions.

[0074] In some embodiments, in any m-th sub-active layer unit, at least the m-th lower sub-active layer with the largest thickness in the first direction among the W-th lower sub-active layers is doped; in any m-th sub-active layer unit, at least the m-th upper sub-active layer with the largest thickness in the first direction among the W-th upper sub-active layers is doped. Since the number of electron tunneling and transitions is relatively large in the m-th lower sub-active layer with the largest thickness in the first direction among the W-th lower sub-active layers and the m-th upper sub-active layers with the largest thickness in the first direction among the W-th upper sub-active layers, doping with ions in the m-th lower sub-active layers and the m-th upper sub-active layers at least at these positions can better adjust the carrier density in the m-th sub-active layer unit.

[0075] In some embodiments, the thinnest of the W lower-m sub-active layers in any m-th sub-active layer unit has a first thickness in a first direction; wherein the first thickness first decreases and then increases with the value of m. The thinnest of the W upper-m sub-active layers in any m-th sub-active layer unit has a second thickness in a first direction, wherein the second thickness first decreases and then increases with the value of m. Through the dimensional differentiation design of the lower-m sub-active layers and the upper-m sub-active layers in different sub-active layer units in the first direction, the wavelength drift of the quantum cascade laser under the actual bias voltage is compensated, and the emission spectral bandwidth is reduced.

[0076] In some embodiments, reference Figure 1The fabrication method of the quantum cascade laser further includes: forming a lower confinement layer 110 and a lower waveguide layer 120 on one side of the substrate layer 100 in a first direction, wherein the lower waveguide layer 120 is located on the side of the lower confinement layer 110 away from the substrate layer 100. The formation of the active layer 130 includes: forming the active layer 130 on the side of the lower waveguide layer 120 away from the lower confinement layer 110. The fabrication method of the quantum cascade laser further includes: forming an upper waveguide layer 140 on the side of the active layer 130 away from the lower waveguide layer 120; forming an upper confinement layer 150 on the side of the upper waveguide layer 140 away from the active layer 130; forming a contact layer 160 on the side of the upper confinement layer 150 away from the upper waveguide layer 140; forming a first electrode layer 170 on the side of the contact layer 160 along the first direction Z away from the upper confinement layer 150; and forming a second electrode layer 180 on the side of the substrate layer 100 away from the lower confinement layer 110.

[0077] The fabrication method of the quantum cascade laser also includes: placing a heat sink 200 on the side of the second electrode layer 180 away from the substrate layer 100.

[0078] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A quantum cascade laser, characterized in that, The active layer includes multiple first sub-active layer units to Mth sub-active layer units stacked sequentially in a first direction, where M is an integer greater than or equal to 2. Each mth sub-active layer unit includes W lower mth sub-active layers and W upper mth sub-active layers, with the lower mth and upper mth sub-active layers stacked alternately in the first direction. Here, m is an integer greater than or equal to 1 and less than or equal to M, and W is an integer greater than or equal to 2. Each mth sub-active layer unit contains Q... m1 The m-th sub-active layer and Q m2 The m-th active layer contains doped ions; where Q m1 Q is an integer greater than or equal to 1 and less than W. m2 An integer greater than or equal to 1 and less than W; Among them, the doping concentration of the doped ions first increases and then decreases as the value of m increases.

2. The quantum cascade laser according to claim 1, characterized in that, ； Among them, z m Let be the coordinates of the center position of the m-th sub-active layer unit in the first direction. Q in the m-th sub-active layer unit m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer Let be the coordinates of the center of the m-th sub-active layer unit with the highest doping concentration in the active layer, in the first direction. , , ,and It is a constant.

3. The quantum cascade laser according to claim 1, characterized in that, The material of any m-th sub-active layer is In x Ga (1-x) As, the material of any m-th sub-active layer is In. y Al (1-y) As.

4. The quantum cascade laser according to claim 1, characterized in that, Q m1 equals Q m2 Or, Q m1 and Q m2 The absolute value of the difference is equal to 1.

5. The quantum cascade laser according to claim 1 or 4, characterized in that, Q m1 Q is 1~2 m2 It is 1~2.

6. The quantum cascade laser according to claim 1, characterized in that, The m-th lower sub-active layer with the largest thickness in the first direction among the W layers in any m-th sub-active layer unit has the doped ions; The upper m-th sub-active layer, which has the largest thickness in the first direction among the W layers of any m-th sub-active layer unit, has the doped ions.

7. The quantum cascade laser according to claim 1, characterized in that, In any m-th sub-active layer unit (WQ) m1 The m-th sub-active layer and (WQ) m1 The m-th active layer is an undoped layer.

8. The quantum cascade laser according to claim 1, characterized in that, In any m-th sub-active layer unit, the thinnest of the W m-th sub-active layers is the m-th sub-active layer, which has a first thickness in the first direction; wherein, the first thickness first decreases and then increases as the value of m increases.

9. The quantum cascade laser according to claim 8, characterized in that, When M is odd, the first thickness decreases as m increases from 1 to (M+1) / 2, and increases as m increases from (M+1) / 2 to M. When M is even, the first thickness decreases as m increases from 1 to (M) / 2, and decreases as m increases from (M / 2+1) to M.

10. The quantum cascade laser according to claim 1 or 8, characterized in that, In any m-th sub-active layer unit, the thinnest of the W m-th sub-active layers is the m-th sub-active layer, which has a second thickness in the first direction. The second thickness decreases and then increases as the value of m increases.

11. The quantum cascade laser according to claim 10, characterized in that, When M is odd, the second thickness decreases as m increases from 1 to (M+1) / 2, and increases as m increases from (M+1) / 2 to M. When M is even, the second thickness decreases as m increases from 1 to (M) / 2, and decreases as m increases from (M / 2+1) to M.

12. The quantum cascade laser according to claim 1, characterized in that, The temperature T(z) of the active layer in the first direction satisfies: ； Where a1, b1, and c1 are constants, z 01 z is a parameter related to temperature distribution. 01 Z represents the position of the active layer with the highest temperature in the first direction, and z represents the position coordinate of the active layer in the first direction. The m-th sub-active layer unit corresponding to the position of the active layer with the highest temperature in the first direction is the same as the m-th sub-active layer unit with the highest doping concentration in the active layer.

13. A method for fabricating a quantum cascade laser, characterized in that, include: Formation of an active layer; The formation of the active layer includes: forming a plurality of first sub-active layer units to Mth sub-active layer units stacked sequentially in a first direction, where M is an integer greater than or equal to 2; any mth sub-active layer unit includes W mth lower sub-active layers and W mth upper sub-active layers; the mth lower sub-active layers and the mth upper sub-active layers are stacked alternately in the first direction, where m is an integer greater than or equal to 1 and less than or equal to M; and W is an integer greater than or equal to 2. In any m-th sub-active layer unit, Q is alternately stacked in the first direction. m1 The m-th sub-active layer and Q m2 Doping is performed on the m-th active layer, where the doping concentration of the dopant ions first increases and then decreases with the increase of the value of m, where Q m1 Q is an integer greater than or equal to 1 and less than W. m2 It is an integer greater than or equal to 1 and less than W.

14. The method for fabricating a quantum cascade laser according to claim 13, characterized in that, in, In any m-th sub-active layer unit, Q is alternately stacked in the first direction. m1 The m-th sub-active layer and Q m2 Doping is performed in the m-th active layer, including: according to In any m-th sub-active layer unit, Q-type elements are alternately stacked in the first direction. m1 The m-th sub-active layer and Q m2 Doping is performed in the m-th active layer; where z m Let be the coordinates of the center position of the m-th sub-active layer unit in the first direction. Q in the m-th sub-active layer unit m1 The m-th sub-active layer and Q m2 The doping concentration of the m-th active layer Let be the coordinates of the center of the m-th sub-active layer unit with the highest doping concentration in the active layer, in the first direction. , , ,and It is a constant.

15. The method for fabricating a quantum cascade laser according to claim 13, characterized in that, Q m1 Q is 1~2 m2 It is 1~2.

16. The method for fabricating a quantum cascade laser according to claim 13, characterized in that, In any m-th sub-active layer unit, at least the m-th lower sub-active layer with the largest thickness in the first direction among the m-th lower sub-active layers of the W layer is doped; in any m-th sub-active layer unit, at least the m-th upper sub-active layer with the largest thickness in the first direction among the m-th upper sub-active layers of the W layer is doped.

17. The method for fabricating a quantum cascade laser according to claim 13, characterized in that, In any m-th sub-active layer unit, the thinnest of the W m-th sub-active layers is the m-th sub-active layer, which has a first thickness in the first direction; wherein, the first thickness first decreases and then increases as the value of m increases.

18. The method for fabricating a quantum cascade laser according to claim 13 or 17, characterized in that, In any m-th sub-active layer unit, the thinnest of the W m-th sub-active layers is the m-th sub-active layer, which has a second thickness in the first direction. The second thickness decreases and then increases as the value of m increases.

19. The method for fabricating a quantum cascade laser according to claim 14, characterized in that, The preparation method also includes: Before doping, the temperature T(z) distribution of the active layer in the first direction is obtained, where T(z) satisfies: Where a1, b1, and c1 are constants, z 01 z is a parameter related to temperature distribution. 01 Z represents the location where the active layer has the highest temperature in the first direction, and z represents the position coordinates of the active layer in the first direction. The center position of the m-th sub-active layer unit corresponding to the position with the highest temperature in the first direction is taken as... The value of .

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