Thermal analysis of short wavelength InGaAs/InAlAs quantum cascade lasers

We report the thermal analysis of short wavelength strain-compensated InxGa1−xAs/InyAl1−yAs quantum cascade lasers (QCLs) operating at λ ∼ 3.8–4.3 μm by a two-dimensional heat transfer model using heat source densities obtained from experimental measurements in continuous-wave mode. The heat fluxes and temperature profiles are analyzed for various QCL structures with different bonding schemes, extracting thermal conductance (Gth). The use of buried heterostructure (BH) enhances the lateral heat dissipation from the active core region of QCLs. The heatsinking structure in epilayer-down configuration using diamond submount exhibits high Gth values with less temperature dependence. For epilayer-down bonded single ridge waveguide 11 μm wide and 4 mm long BH QCLs at λ ∼ 3.8 μm and λ ∼ 4.3 μm on diamond submount, the improved Gth values of 292 W/K cm2 and 409 W/K cm2 at 298 K are obtained, respectively. The highly strained InGaAs/InAlAs structure gives a low Gth value due to the reduced thermal conductivity. The theoretically calculated results are compared with the existing Gth data obtained experimentally, thus showing a good agreement.