Output facet heating mechanism for uncoated high power long wave infrared quantum cascade lasers

Abstract

Output facet temperatures of an uncoated high power continuous-wave quantum cascade laser (QCL) emitting at 8.5 μm were measured by using micro-Raman thermometry. The rate of the measured temperature changes with the injected electrical power increased from 6.5 K/W below the laser threshold to 12.3 K/W above the threshold. In addition, the measured temperature rise exceeded 220 K at an optical power of 0.9 W, well above the model projections based only on Joule heating. Facet oxidation was characterized via x-ray photoelectron spectroscopy measurements at incremental etch depths. While the oxidation reactions of InP and Ga were observed only at the surface level, the measured penetration of native Al2O3 was ∼24 nm. COMSOL thermal modeling demonstrated that light reabsorption by the native Al2O3 layer could well explain the additional temperature rise above the threshold. These results suggest that facet oxidation must be addressed to ensure the reliability of high-power long wave infrared QCLs.

From Two- to Three-Dimensional Model of Heat Flow in Edge-Emitting Laser: Theory, Experiment and Numerical Tools

“…In the case of a bipolar device (like our InGaAs/GaAs/AlGaAs laser), it can incorporate such heating mechanisms as surface recombination, reabsorption of radiation, Joule, and bulk heating. Unipolar device (i.e., quantum cascade laser) is heated mainly due to dissipative quantum transport processes in the active layer [27] and-in the vicinity of output mirror-due to reabsorption of radiation [28]. Thus, g m and g a should be recalculated adequately, but the shape of the function itself may remain unchanged.…”

High-Power Mid-Infrared (λ∼3-6 μm) Quantum Cascade Lasers

“…Note that no correlation has been established between these facet failures and optical-power density at the facet, except for longer wavelength (~8m) devices with uncoated facets [68] for which an oxide, absorbing at ~ 8 m wavelength, formed on the emitting facet. At high power output ( >1 W) operating conditions, a large amount of heat is generated in the core region of the devices.…”

Near‐Field Thermal Profiling and 3D Anisotropic Thermal Analysis of Quantum Cascade Lasers

“…Techniques for temperature monitoring include micro‐photoluminescence, [ 16 ] Raman spectroscopy, [ 17 ] thermoreflectance spectroscopy, [ 18 ] lock‐in IR Thermography, [ 19 ] and infrared scanning near field optical microscopy (IR‐SNOM). [ 20 ] For example, Raman spectroscopy as a non‐contact thermometer was used to study output facet heating in an uncoated high‐power continuous‐wave QCL emitting at 8.5 μm.…”

“…[ 20 ] For example, Raman spectroscopy as a non‐contact thermometer was used to study output facet heating in an uncoated high‐power continuous‐wave QCL emitting at 8.5 μm. [ 17 ] A comparison of the spatial and temperature resolutions of these techniques can be found in Ref. [21]…”

“…[9][10][11] However, the low thermal conductivity of QCL's multilayer superlattice gain medium and the ample operational electrical power cause significant self-heating in QCLs, [12,13] which, over time, results in a rise in lasing threshold current, [6] a decrease in output power, [14] and even device failure. [15] Therefore, to better understand QCL's failure mechanism, thermal analysis and monitoring are necessary for designing QCLs with optimal performance.Techniques for temperature monitoring include microphotoluminescence, [16] Raman spectroscopy, [17] thermoreflectance spectroscopy, [18] lock-in IR Thermography, [19] and infrared scanning near field optical microscopy (IR-SNOM). [20] For example, Raman spectroscopy as a non-contact thermometer was used to study output facet heating in an uncoated high-power continuous-wave QCL emitting at 8.5 μm.…”