The Experts below are selected from a list of 6333 Experts worldwide ranked by ideXlab platform

D Botez - One of the best experts on this subject based on the ideXlab platform.

  • highly efficient 8 μm emitting step taper active region quantum cascade lasers
    AIP Advances, 2021
    Co-Authors: K Oresick, L J Mawst, J D Kirch, D Botez
    Abstract:

    Recently, it was shown for 4.5 μm–5.0 μm-emitting, state-of-the-art quantum cascade lasers (QCLs) that the internal efficiency can be fully accounted for when considering interface-roughness (IFR)-triggered Carrier Leakage from both the upper-laser (ul) level and key injector states. By applying the same formalism to ∼8.0 μm-emitting QCLs of a step-taper active-region (STA) design, we find that the devices’ internal efficiency reaches a high value of ∼76%. That is partly due to a record-high injection-efficiency value (89%), as a result of strong Carrier-Leakage suppression, and partly due to an IFR-scattering enhanced laser-transition efficiency value of 85.2%. By comparison, when the same analysis is applied to conventional ∼8.0 μm-emitting QCLs, grown by the same crystal-growth technique: metal–organic chemical vapor deposition (MOCVD), the internal efficiency is found to be only ∼59%, typical of values extracted from experimental data of mid-infrared-emitting conventional QCLs. When further comparing the ∼8.0 μm-emitting STA QCLs with conventional QCLs, the ul-level lifetime is found to be controlled by both LO-phonon and alloy-disorder scattering, similar to what we recently found for 4.5 μm–5.0 μm-emitting QCLs. However, unlike 4.5 μm–5.0 μm-emitting QCLs, the lower-laser level lifetime is found to be controlled by both LO-phonon and IFR scattering. In addition to the high internal-efficiency value, the use of excited-state injection and a low voltage defect result in the STA QCL reaching a front-facet wall-plug efficiency value of 10.6%, a record-high, front-facet value for 8 μm–11 μm-emitting QCLs grown by MOCVD and holding potential for continuous-wave operation.

  • Carrier Leakage via interface roughness scattering bridges gap between theoretical and experimental internal efficiencies of quantum cascade lasers
    Applied Physics Letters, 2020
    Co-Authors: C Boyle, Yuri V. Flores, L J Mawst, K Oresick, J Kirch, D Botez
    Abstract:

    When conventionally calculating Carrier Leakage for state-of-the-art quantum cascade lasers (QCLs), that is, LO-phonon-assisted Leakage from the upper laser level via electron thermal excitation to high-energy active-region (AR) states, followed by relaxation to low-energy AR states, ∼18%-wide gaps were recently found between calculated and experimentally measured internal efficiency values. We incorporate elastic scattering [i.e., interface-roughness (IFR) and alloy-disorder scattering] into the Carrier-Leakage process and consider Carrier Leakage from key injector states as well. In addition, the expressions for LO-phonon and IFR-triggered Carrier-Leakage currents take into account the large percentage of thermally excited electrons that return back to initial states via both inelastic and elastic scattering. As a result, we find that the gaps between theoretical and experimental internal efficiency values are essentially bridged. Another finding is that, for the investigated state-of-the-art structures, IFR scattering causes the total Carrier Leakage to reach values as much as an order of magnitude higher than conventional inelastic scattering-only Leakage. The developed formalism opens the way to significantly increase the internal efficiency (i.e., to more than 80%) via IFR-scattering engineering, such that maximum wall-plug efficiencies close to projected fundamental, both-facets values (e.g., 42% at λ = 4.6 μm) can be achieved. By employing this formalism, we reached a 4.6 μm-emitting-QCL preliminary design for suppressing IFR-triggered Carrier Leakage, which provides an internal efficiency of 86% as well as a projected single-facet wall-plug efficiency value of 36% at a heatsink temperature of 300 K.

  • high efficiency high power mid infrared quantum cascade lasers invited
    Optical Materials Express, 2018
    Co-Authors: D Botez, C Boyle, K Oresick, J D Kirch, D Lindberg, C Sigler, Honghyuk Kim, B Knipfer, Jae Ha Ryu, T Earles
    Abstract:

    The step-taper active-region (STA) design concept is implemented for ~5.0 μm-emitting quantum cascade lasers (QCLs) grown by metal-organic chemical vapor deposition (MOCVD). Carrier-Leakage suppression yields high characteristic temperatures for the threshold-current density Jth, T0, and for the slope efficiency ηsl, T1: 226 K and 653 K. Resonant-tunneling extraction from the lower level results in miniband-like extraction. In turn, the internal efficiency ηi is found, from a variable mirror-loss study, to be ~77%; thus approaching the ~90% upper limit, when employing only inelastic scattering. Considering interface-roughness and alloy-disorder scattering, the transition efficiency reaches values of ~95%. Then, the injection efficiency is ~81%, and, for λ = 4.6 μm, the wallplug-efficiency ηwp upper limit reaches 41.2%. Results include 4.2 W/A single-facet ηsl and 0.96 kA/cm2Jth values. Buried-heterostructure (BH) QCLs provide single-facet 2.6 W continuous-wave (CW) power and 12% CW ηwp. Optimized 8 μm-emitting, STA-design QCLs provide 2 W/A ηsl, and 1.1 kA/cm2Jth; and BH devices yield single-facet 1 W CW power and 6% CW ηwp.

  • high internal differential efficiency mid infrared quantum cascade lasers
    Proceedings of SPIE, 2017
    Co-Authors: D Botez, L J Mawst, C Boyle, K Oresick, J Kirch, Jae Cheol Shin, C C Chang, C Sigler, Minhyeok Jo, D Lindberg
    Abstract:

    Implementation of the step-taper active-region (STA) design to 8-9 μm-emitting quantum cascade lasers (QCLs) has resulted in both high T0 and T1 values: 220 K and 665 K, and short lower-level lifetimes: 0.12 ps. In turn, the internal differential efficiency ηid, which is the product of the injection efficiency and the differential laser-transition efficiency, reaches values as high as 86 % for both 8.4 μm- and 8.8 μm-emitting QCLs. Such ηid values are 30-50% higher than those obtained from conventional QCLs emitting in the 7-11 μm wavelength range. Achieving both Carrier-Leakage suppression and miniband-like Carrier extraction in mid-infrared (IR) QCLs leads to ηid values close to the fundamental limit of ~ 90 %. In turn, the currently employed fundamental wallplug-efficiency limits over the mid-IR wavelength range have to be increased by ~ 34 % (e.g., the wallplug-efficiency limit at λ= 4.6 μm increases from 29 % to 39 %). Preliminary results from STA-type 4.8-5.0 μm-emitting QCLs include 1.5 W CW operation, and 77 % internal differential efficiency; that is, 30-50% higher than the ηid values obtained from conventional 4.0-6.5μm-emitting QCLs.

  • 86 internal differential efficiency from 8 to 9 µm emitting step taper active region quantum cascade lasers
    Optics Express, 2016
    Co-Authors: J Kirch, L J Mawst, C Boyle, D Lindberg, T Earles, C C Chang, D Botez
    Abstract:

    : 8.4 μm-emitting quantum cascade lasers (QCLs) have been designed to have, right from threshold, both Carrier-Leakage suppression and miniband-like Carrier extraction. The slope-efficiency characteristic temperature T1, the signature of Carrier-Leakage suppression, is found to be 665 K. Resonant-tunneling Carrier extraction from both the lower laser level (ll) and the level below it, coupled with highly effective ll-depopulation provide a very short ll lifetime (~0.12 ps). As a result the laser-transition differential efficiency reaches 89%, and the internal differential efficiency ηid, derived from a variable mirror-loss study, is found to be 86%, in good agreement with theory. A study of 8.8 μm-emitting QCLs also provides an ηid value of 86%. A corrected equation for the external differential efficiency is derived which leads to a fundamental limit of ~90% for the ηid values of mid-infrared QCLs. In turn, the fundamental wallplug-efficiency limits become ~34% higher than previously predicted.

L J Mawst - One of the best experts on this subject based on the ideXlab platform.

  • highly efficient 8 μm emitting step taper active region quantum cascade lasers
    AIP Advances, 2021
    Co-Authors: K Oresick, L J Mawst, J D Kirch, D Botez
    Abstract:

    Recently, it was shown for 4.5 μm–5.0 μm-emitting, state-of-the-art quantum cascade lasers (QCLs) that the internal efficiency can be fully accounted for when considering interface-roughness (IFR)-triggered Carrier Leakage from both the upper-laser (ul) level and key injector states. By applying the same formalism to ∼8.0 μm-emitting QCLs of a step-taper active-region (STA) design, we find that the devices’ internal efficiency reaches a high value of ∼76%. That is partly due to a record-high injection-efficiency value (89%), as a result of strong Carrier-Leakage suppression, and partly due to an IFR-scattering enhanced laser-transition efficiency value of 85.2%. By comparison, when the same analysis is applied to conventional ∼8.0 μm-emitting QCLs, grown by the same crystal-growth technique: metal–organic chemical vapor deposition (MOCVD), the internal efficiency is found to be only ∼59%, typical of values extracted from experimental data of mid-infrared-emitting conventional QCLs. When further comparing the ∼8.0 μm-emitting STA QCLs with conventional QCLs, the ul-level lifetime is found to be controlled by both LO-phonon and alloy-disorder scattering, similar to what we recently found for 4.5 μm–5.0 μm-emitting QCLs. However, unlike 4.5 μm–5.0 μm-emitting QCLs, the lower-laser level lifetime is found to be controlled by both LO-phonon and IFR scattering. In addition to the high internal-efficiency value, the use of excited-state injection and a low voltage defect result in the STA QCL reaching a front-facet wall-plug efficiency value of 10.6%, a record-high, front-facet value for 8 μm–11 μm-emitting QCLs grown by MOCVD and holding potential for continuous-wave operation.

  • Carrier Leakage via interface roughness scattering bridges gap between theoretical and experimental internal efficiencies of quantum cascade lasers
    Applied Physics Letters, 2020
    Co-Authors: C Boyle, Yuri V. Flores, L J Mawst, K Oresick, J Kirch, D Botez
    Abstract:

    When conventionally calculating Carrier Leakage for state-of-the-art quantum cascade lasers (QCLs), that is, LO-phonon-assisted Leakage from the upper laser level via electron thermal excitation to high-energy active-region (AR) states, followed by relaxation to low-energy AR states, ∼18%-wide gaps were recently found between calculated and experimentally measured internal efficiency values. We incorporate elastic scattering [i.e., interface-roughness (IFR) and alloy-disorder scattering] into the Carrier-Leakage process and consider Carrier Leakage from key injector states as well. In addition, the expressions for LO-phonon and IFR-triggered Carrier-Leakage currents take into account the large percentage of thermally excited electrons that return back to initial states via both inelastic and elastic scattering. As a result, we find that the gaps between theoretical and experimental internal efficiency values are essentially bridged. Another finding is that, for the investigated state-of-the-art structures, IFR scattering causes the total Carrier Leakage to reach values as much as an order of magnitude higher than conventional inelastic scattering-only Leakage. The developed formalism opens the way to significantly increase the internal efficiency (i.e., to more than 80%) via IFR-scattering engineering, such that maximum wall-plug efficiencies close to projected fundamental, both-facets values (e.g., 42% at λ = 4.6 μm) can be achieved. By employing this formalism, we reached a 4.6 μm-emitting-QCL preliminary design for suppressing IFR-triggered Carrier Leakage, which provides an internal efficiency of 86% as well as a projected single-facet wall-plug efficiency value of 36% at a heatsink temperature of 300 K.

  • high internal differential efficiency mid infrared quantum cascade lasers
    Proceedings of SPIE, 2017
    Co-Authors: D Botez, L J Mawst, C Boyle, K Oresick, J Kirch, Jae Cheol Shin, C C Chang, C Sigler, Minhyeok Jo, D Lindberg
    Abstract:

    Implementation of the step-taper active-region (STA) design to 8-9 μm-emitting quantum cascade lasers (QCLs) has resulted in both high T0 and T1 values: 220 K and 665 K, and short lower-level lifetimes: 0.12 ps. In turn, the internal differential efficiency ηid, which is the product of the injection efficiency and the differential laser-transition efficiency, reaches values as high as 86 % for both 8.4 μm- and 8.8 μm-emitting QCLs. Such ηid values are 30-50% higher than those obtained from conventional QCLs emitting in the 7-11 μm wavelength range. Achieving both Carrier-Leakage suppression and miniband-like Carrier extraction in mid-infrared (IR) QCLs leads to ηid values close to the fundamental limit of ~ 90 %. In turn, the currently employed fundamental wallplug-efficiency limits over the mid-IR wavelength range have to be increased by ~ 34 % (e.g., the wallplug-efficiency limit at λ= 4.6 μm increases from 29 % to 39 %). Preliminary results from STA-type 4.8-5.0 μm-emitting QCLs include 1.5 W CW operation, and 77 % internal differential efficiency; that is, 30-50% higher than the ηid values obtained from conventional 4.0-6.5μm-emitting QCLs.

  • 86 internal differential efficiency from 8 to 9 µm emitting step taper active region quantum cascade lasers
    Optics Express, 2016
    Co-Authors: J Kirch, L J Mawst, C Boyle, D Lindberg, T Earles, C C Chang, D Botez
    Abstract:

    : 8.4 μm-emitting quantum cascade lasers (QCLs) have been designed to have, right from threshold, both Carrier-Leakage suppression and miniband-like Carrier extraction. The slope-efficiency characteristic temperature T1, the signature of Carrier-Leakage suppression, is found to be 665 K. Resonant-tunneling Carrier extraction from both the lower laser level (ll) and the level below it, coupled with highly effective ll-depopulation provide a very short ll lifetime (~0.12 ps). As a result the laser-transition differential efficiency reaches 89%, and the internal differential efficiency ηid, derived from a variable mirror-loss study, is found to be 86%, in good agreement with theory. A study of 8.8 μm-emitting QCLs also provides an ηid value of 86%. A corrected equation for the external differential efficiency is derived which leads to a fundamental limit of ~90% for the ηid values of mid-infrared QCLs. In turn, the fundamental wallplug-efficiency limits become ~34% higher than previously predicted.

  • step taper active region quantum cascade lasers for Carrier Leakage suppression and high internal differential efficiency
    Proceedings of SPIE, 2016
    Co-Authors: J D Kirch, L J Mawst, C Boyle, Chun Chieh Chang, T Earles, D Lindberg, D Botez
    Abstract:

    By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting quantum cascade lasers (QCLs) virtually complete Carrier-Leakage suppression is achieved, as evidenced by high values for both the threshold-current characteristic temperature coefficient T 0 (283 K and 242 K) and the slope-efficiency characteristic temperature coefficient T 1 (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm 2 and 1.88 kA/cm 2 , respectively. In addition, due to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30- 40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both efficient Carrier-Leakage suppression as well as fast and efficient Carrier extraction, the values for the internal differential efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting in the 7-11 μm wavelength range.

T Earles - One of the best experts on this subject based on the ideXlab platform.

  • high efficiency high power mid infrared quantum cascade lasers invited
    Optical Materials Express, 2018
    Co-Authors: D Botez, C Boyle, K Oresick, J D Kirch, D Lindberg, C Sigler, Honghyuk Kim, B Knipfer, Jae Ha Ryu, T Earles
    Abstract:

    The step-taper active-region (STA) design concept is implemented for ~5.0 μm-emitting quantum cascade lasers (QCLs) grown by metal-organic chemical vapor deposition (MOCVD). Carrier-Leakage suppression yields high characteristic temperatures for the threshold-current density Jth, T0, and for the slope efficiency ηsl, T1: 226 K and 653 K. Resonant-tunneling extraction from the lower level results in miniband-like extraction. In turn, the internal efficiency ηi is found, from a variable mirror-loss study, to be ~77%; thus approaching the ~90% upper limit, when employing only inelastic scattering. Considering interface-roughness and alloy-disorder scattering, the transition efficiency reaches values of ~95%. Then, the injection efficiency is ~81%, and, for λ = 4.6 μm, the wallplug-efficiency ηwp upper limit reaches 41.2%. Results include 4.2 W/A single-facet ηsl and 0.96 kA/cm2Jth values. Buried-heterostructure (BH) QCLs provide single-facet 2.6 W continuous-wave (CW) power and 12% CW ηwp. Optimized 8 μm-emitting, STA-design QCLs provide 2 W/A ηsl, and 1.1 kA/cm2Jth; and BH devices yield single-facet 1 W CW power and 6% CW ηwp.

  • 86 internal differential efficiency from 8 to 9 µm emitting step taper active region quantum cascade lasers
    Optics Express, 2016
    Co-Authors: J Kirch, L J Mawst, C Boyle, D Lindberg, T Earles, C C Chang, D Botez
    Abstract:

    : 8.4 μm-emitting quantum cascade lasers (QCLs) have been designed to have, right from threshold, both Carrier-Leakage suppression and miniband-like Carrier extraction. The slope-efficiency characteristic temperature T1, the signature of Carrier-Leakage suppression, is found to be 665 K. Resonant-tunneling Carrier extraction from both the lower laser level (ll) and the level below it, coupled with highly effective ll-depopulation provide a very short ll lifetime (~0.12 ps). As a result the laser-transition differential efficiency reaches 89%, and the internal differential efficiency ηid, derived from a variable mirror-loss study, is found to be 86%, in good agreement with theory. A study of 8.8 μm-emitting QCLs also provides an ηid value of 86%. A corrected equation for the external differential efficiency is derived which leads to a fundamental limit of ~90% for the ηid values of mid-infrared QCLs. In turn, the fundamental wallplug-efficiency limits become ~34% higher than previously predicted.

  • highly temperature insensitive low threshold current density λ 8 7 8 8 μm quantum cascade lasers
    Applied Physics Letters, 2015
    Co-Authors: J D Kirch, L J Mawst, C Boyle, Chun Chieh Chang, D Lindberg, T Earles, D Botez
    Abstract:

    By stepwise tapering, both the barrier heights and quantum-well depths in the active regions of 8.7–8.8 μm-emitting quantum-cascade-laser (QCL) structures, virtually complete Carrier-Leakage suppression is achieved. Such step-taper active-region-type QCLs possess, for 3 mm-long devices with high-reflectivity-coated back facets, threshold-current characteristic temperature coefficients, T0, as high as 283 K and slope-efficiency characteristic temperature coefficients, T1, as high as 561 K, over the 20–60 °C heatsink-temperature range. These high T0 and T1 values reflect at least a factor of four reduction in Carrier-Leakage current compared to conventional 8–9 μm-emitting QCLs. Room temperature, pulsed, threshold-current densities are 1.58 kA/cm2; values comparable to those for 35-period conventional QCLs of similar injector-region doping level. Superlinear behavior of the light-current curves is shown to be the result of the onset of resonant extraction from the lower laser level at a drive level of ∼1.3×...

  • multidimensional conduction band engineering for maximizing the continuous wave cw wallplug efficiencies of mid infrared quantum cascade lasers
    IEEE Journal of Selected Topics in Quantum Electronics, 2013
    Co-Authors: D Botez, L J Mawst, J D Kirch, Chun Chieh Chang, Jae Cheol Shin, T Earles
    Abstract:

    By tailoring the active-region quantum wells and barriers of 4.5-5.0-μm-emitting quantum cascade lasers (QCLs), the device performances dramatically improve. Deep-well QCLs significantly suppress Carrier Leakage, as evidenced by high values for the threshold-current characteristic temperature T0 (253 K) and the slope-efficiency characteristic temperature T1 (285 K), but, due to stronger quantum confinement, the global upper-laser-level lifetime τ4g decreases, resulting in basically the same room-temperature (RT) threshold-current density Jth as conventional QCLs. Tapered active-region (TA) QCLs, devices for which the active-region barrier heights increase in energy from the injection to the exit barriers, lead to recovery of the τ4g value while further suppressing Carrier Leakage. As a result, experimental RT Jth values from moderate-taper TA 4.8-μm emitting QCLs are ~14% less than for conventional QCLs and T1 reaches values as high as 797 K. A step-taper TA (STA) QCL design provides both complete Carrier-Leakage suppression and an increase in the τ4g value, due to Stark-effect reduction and strong asymmetry. Then, the RT Jth value decreases by at least 25% compared to conventional QCLs of same geometry. In turn, single-facet, RT pulsed and continuous-wave maximum wallplug-efficiency values of 29% and 27% are projected for 4.6-4.8-μm-emitting QCLs.

J D Kirch - One of the best experts on this subject based on the ideXlab platform.

  • highly efficient 8 μm emitting step taper active region quantum cascade lasers
    AIP Advances, 2021
    Co-Authors: K Oresick, L J Mawst, J D Kirch, D Botez
    Abstract:

    Recently, it was shown for 4.5 μm–5.0 μm-emitting, state-of-the-art quantum cascade lasers (QCLs) that the internal efficiency can be fully accounted for when considering interface-roughness (IFR)-triggered Carrier Leakage from both the upper-laser (ul) level and key injector states. By applying the same formalism to ∼8.0 μm-emitting QCLs of a step-taper active-region (STA) design, we find that the devices’ internal efficiency reaches a high value of ∼76%. That is partly due to a record-high injection-efficiency value (89%), as a result of strong Carrier-Leakage suppression, and partly due to an IFR-scattering enhanced laser-transition efficiency value of 85.2%. By comparison, when the same analysis is applied to conventional ∼8.0 μm-emitting QCLs, grown by the same crystal-growth technique: metal–organic chemical vapor deposition (MOCVD), the internal efficiency is found to be only ∼59%, typical of values extracted from experimental data of mid-infrared-emitting conventional QCLs. When further comparing the ∼8.0 μm-emitting STA QCLs with conventional QCLs, the ul-level lifetime is found to be controlled by both LO-phonon and alloy-disorder scattering, similar to what we recently found for 4.5 μm–5.0 μm-emitting QCLs. However, unlike 4.5 μm–5.0 μm-emitting QCLs, the lower-laser level lifetime is found to be controlled by both LO-phonon and IFR scattering. In addition to the high internal-efficiency value, the use of excited-state injection and a low voltage defect result in the STA QCL reaching a front-facet wall-plug efficiency value of 10.6%, a record-high, front-facet value for 8 μm–11 μm-emitting QCLs grown by MOCVD and holding potential for continuous-wave operation.

  • high efficiency high power mid infrared quantum cascade lasers invited
    Optical Materials Express, 2018
    Co-Authors: D Botez, C Boyle, K Oresick, J D Kirch, D Lindberg, C Sigler, Honghyuk Kim, B Knipfer, Jae Ha Ryu, T Earles
    Abstract:

    The step-taper active-region (STA) design concept is implemented for ~5.0 μm-emitting quantum cascade lasers (QCLs) grown by metal-organic chemical vapor deposition (MOCVD). Carrier-Leakage suppression yields high characteristic temperatures for the threshold-current density Jth, T0, and for the slope efficiency ηsl, T1: 226 K and 653 K. Resonant-tunneling extraction from the lower level results in miniband-like extraction. In turn, the internal efficiency ηi is found, from a variable mirror-loss study, to be ~77%; thus approaching the ~90% upper limit, when employing only inelastic scattering. Considering interface-roughness and alloy-disorder scattering, the transition efficiency reaches values of ~95%. Then, the injection efficiency is ~81%, and, for λ = 4.6 μm, the wallplug-efficiency ηwp upper limit reaches 41.2%. Results include 4.2 W/A single-facet ηsl and 0.96 kA/cm2Jth values. Buried-heterostructure (BH) QCLs provide single-facet 2.6 W continuous-wave (CW) power and 12% CW ηwp. Optimized 8 μm-emitting, STA-design QCLs provide 2 W/A ηsl, and 1.1 kA/cm2Jth; and BH devices yield single-facet 1 W CW power and 6% CW ηwp.

  • step taper active region quantum cascade lasers for Carrier Leakage suppression and high internal differential efficiency
    Proceedings of SPIE, 2016
    Co-Authors: J D Kirch, L J Mawst, C Boyle, Chun Chieh Chang, T Earles, D Lindberg, D Botez
    Abstract:

    By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting quantum cascade lasers (QCLs) virtually complete Carrier-Leakage suppression is achieved, as evidenced by high values for both the threshold-current characteristic temperature coefficient T 0 (283 K and 242 K) and the slope-efficiency characteristic temperature coefficient T 1 (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm 2 and 1.88 kA/cm 2 , respectively. In addition, due to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30- 40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both efficient Carrier-Leakage suppression as well as fast and efficient Carrier extraction, the values for the internal differential efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting in the 7-11 μm wavelength range.

  • highly temperature insensitive low threshold current density λ 8 7 8 8 μm quantum cascade lasers
    Applied Physics Letters, 2015
    Co-Authors: J D Kirch, L J Mawst, C Boyle, Chun Chieh Chang, D Lindberg, T Earles, D Botez
    Abstract:

    By stepwise tapering, both the barrier heights and quantum-well depths in the active regions of 8.7–8.8 μm-emitting quantum-cascade-laser (QCL) structures, virtually complete Carrier-Leakage suppression is achieved. Such step-taper active-region-type QCLs possess, for 3 mm-long devices with high-reflectivity-coated back facets, threshold-current characteristic temperature coefficients, T0, as high as 283 K and slope-efficiency characteristic temperature coefficients, T1, as high as 561 K, over the 20–60 °C heatsink-temperature range. These high T0 and T1 values reflect at least a factor of four reduction in Carrier-Leakage current compared to conventional 8–9 μm-emitting QCLs. Room temperature, pulsed, threshold-current densities are 1.58 kA/cm2; values comparable to those for 35-period conventional QCLs of similar injector-region doping level. Superlinear behavior of the light-current curves is shown to be the result of the onset of resonant extraction from the lower laser level at a drive level of ∼1.3×...

  • multidimensional conduction band engineering for maximizing the continuous wave cw wallplug efficiencies of mid infrared quantum cascade lasers
    IEEE Journal of Selected Topics in Quantum Electronics, 2013
    Co-Authors: D Botez, L J Mawst, J D Kirch, Chun Chieh Chang, Jae Cheol Shin, T Earles
    Abstract:

    By tailoring the active-region quantum wells and barriers of 4.5-5.0-μm-emitting quantum cascade lasers (QCLs), the device performances dramatically improve. Deep-well QCLs significantly suppress Carrier Leakage, as evidenced by high values for the threshold-current characteristic temperature T0 (253 K) and the slope-efficiency characteristic temperature T1 (285 K), but, due to stronger quantum confinement, the global upper-laser-level lifetime τ4g decreases, resulting in basically the same room-temperature (RT) threshold-current density Jth as conventional QCLs. Tapered active-region (TA) QCLs, devices for which the active-region barrier heights increase in energy from the injection to the exit barriers, lead to recovery of the τ4g value while further suppressing Carrier Leakage. As a result, experimental RT Jth values from moderate-taper TA 4.8-μm emitting QCLs are ~14% less than for conventional QCLs and T1 reaches values as high as 797 K. A step-taper TA (STA) QCL design provides both complete Carrier-Leakage suppression and an increase in the τ4g value, due to Stark-effect reduction and strong asymmetry. Then, the RT Jth value decreases by at least 25% compared to conventional QCLs of same geometry. In turn, single-facet, RT pulsed and continuous-wave maximum wallplug-efficiency values of 29% and 27% are projected for 4.6-4.8-μm-emitting QCLs.

C Boyle - One of the best experts on this subject based on the ideXlab platform.

  • Carrier Leakage via interface roughness scattering bridges gap between theoretical and experimental internal efficiencies of quantum cascade lasers
    Applied Physics Letters, 2020
    Co-Authors: C Boyle, Yuri V. Flores, L J Mawst, K Oresick, J Kirch, D Botez
    Abstract:

    When conventionally calculating Carrier Leakage for state-of-the-art quantum cascade lasers (QCLs), that is, LO-phonon-assisted Leakage from the upper laser level via electron thermal excitation to high-energy active-region (AR) states, followed by relaxation to low-energy AR states, ∼18%-wide gaps were recently found between calculated and experimentally measured internal efficiency values. We incorporate elastic scattering [i.e., interface-roughness (IFR) and alloy-disorder scattering] into the Carrier-Leakage process and consider Carrier Leakage from key injector states as well. In addition, the expressions for LO-phonon and IFR-triggered Carrier-Leakage currents take into account the large percentage of thermally excited electrons that return back to initial states via both inelastic and elastic scattering. As a result, we find that the gaps between theoretical and experimental internal efficiency values are essentially bridged. Another finding is that, for the investigated state-of-the-art structures, IFR scattering causes the total Carrier Leakage to reach values as much as an order of magnitude higher than conventional inelastic scattering-only Leakage. The developed formalism opens the way to significantly increase the internal efficiency (i.e., to more than 80%) via IFR-scattering engineering, such that maximum wall-plug efficiencies close to projected fundamental, both-facets values (e.g., 42% at λ = 4.6 μm) can be achieved. By employing this formalism, we reached a 4.6 μm-emitting-QCL preliminary design for suppressing IFR-triggered Carrier Leakage, which provides an internal efficiency of 86% as well as a projected single-facet wall-plug efficiency value of 36% at a heatsink temperature of 300 K.

  • high efficiency high power mid infrared quantum cascade lasers invited
    Optical Materials Express, 2018
    Co-Authors: D Botez, C Boyle, K Oresick, J D Kirch, D Lindberg, C Sigler, Honghyuk Kim, B Knipfer, Jae Ha Ryu, T Earles
    Abstract:

    The step-taper active-region (STA) design concept is implemented for ~5.0 μm-emitting quantum cascade lasers (QCLs) grown by metal-organic chemical vapor deposition (MOCVD). Carrier-Leakage suppression yields high characteristic temperatures for the threshold-current density Jth, T0, and for the slope efficiency ηsl, T1: 226 K and 653 K. Resonant-tunneling extraction from the lower level results in miniband-like extraction. In turn, the internal efficiency ηi is found, from a variable mirror-loss study, to be ~77%; thus approaching the ~90% upper limit, when employing only inelastic scattering. Considering interface-roughness and alloy-disorder scattering, the transition efficiency reaches values of ~95%. Then, the injection efficiency is ~81%, and, for λ = 4.6 μm, the wallplug-efficiency ηwp upper limit reaches 41.2%. Results include 4.2 W/A single-facet ηsl and 0.96 kA/cm2Jth values. Buried-heterostructure (BH) QCLs provide single-facet 2.6 W continuous-wave (CW) power and 12% CW ηwp. Optimized 8 μm-emitting, STA-design QCLs provide 2 W/A ηsl, and 1.1 kA/cm2Jth; and BH devices yield single-facet 1 W CW power and 6% CW ηwp.

  • high internal differential efficiency mid infrared quantum cascade lasers
    Proceedings of SPIE, 2017
    Co-Authors: D Botez, L J Mawst, C Boyle, K Oresick, J Kirch, Jae Cheol Shin, C C Chang, C Sigler, Minhyeok Jo, D Lindberg
    Abstract:

    Implementation of the step-taper active-region (STA) design to 8-9 μm-emitting quantum cascade lasers (QCLs) has resulted in both high T0 and T1 values: 220 K and 665 K, and short lower-level lifetimes: 0.12 ps. In turn, the internal differential efficiency ηid, which is the product of the injection efficiency and the differential laser-transition efficiency, reaches values as high as 86 % for both 8.4 μm- and 8.8 μm-emitting QCLs. Such ηid values are 30-50% higher than those obtained from conventional QCLs emitting in the 7-11 μm wavelength range. Achieving both Carrier-Leakage suppression and miniband-like Carrier extraction in mid-infrared (IR) QCLs leads to ηid values close to the fundamental limit of ~ 90 %. In turn, the currently employed fundamental wallplug-efficiency limits over the mid-IR wavelength range have to be increased by ~ 34 % (e.g., the wallplug-efficiency limit at λ= 4.6 μm increases from 29 % to 39 %). Preliminary results from STA-type 4.8-5.0 μm-emitting QCLs include 1.5 W CW operation, and 77 % internal differential efficiency; that is, 30-50% higher than the ηid values obtained from conventional 4.0-6.5μm-emitting QCLs.

  • 86 internal differential efficiency from 8 to 9 µm emitting step taper active region quantum cascade lasers
    Optics Express, 2016
    Co-Authors: J Kirch, L J Mawst, C Boyle, D Lindberg, T Earles, C C Chang, D Botez
    Abstract:

    : 8.4 μm-emitting quantum cascade lasers (QCLs) have been designed to have, right from threshold, both Carrier-Leakage suppression and miniband-like Carrier extraction. The slope-efficiency characteristic temperature T1, the signature of Carrier-Leakage suppression, is found to be 665 K. Resonant-tunneling Carrier extraction from both the lower laser level (ll) and the level below it, coupled with highly effective ll-depopulation provide a very short ll lifetime (~0.12 ps). As a result the laser-transition differential efficiency reaches 89%, and the internal differential efficiency ηid, derived from a variable mirror-loss study, is found to be 86%, in good agreement with theory. A study of 8.8 μm-emitting QCLs also provides an ηid value of 86%. A corrected equation for the external differential efficiency is derived which leads to a fundamental limit of ~90% for the ηid values of mid-infrared QCLs. In turn, the fundamental wallplug-efficiency limits become ~34% higher than previously predicted.

  • step taper active region quantum cascade lasers for Carrier Leakage suppression and high internal differential efficiency
    Proceedings of SPIE, 2016
    Co-Authors: J D Kirch, L J Mawst, C Boyle, Chun Chieh Chang, T Earles, D Lindberg, D Botez
    Abstract:

    By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting quantum cascade lasers (QCLs) virtually complete Carrier-Leakage suppression is achieved, as evidenced by high values for both the threshold-current characteristic temperature coefficient T 0 (283 K and 242 K) and the slope-efficiency characteristic temperature coefficient T 1 (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm 2 and 1.88 kA/cm 2 , respectively. In addition, due to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30- 40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both efficient Carrier-Leakage suppression as well as fast and efficient Carrier extraction, the values for the internal differential efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting in the 7-11 μm wavelength range.