Thermal analysis of InP-based quantum cascade lasers for efficient heat dissipation

We have theoretically investigated the thermal characteristics of double-channel ridge-waveguide InGaAs/InAlAs/InP quantum cascade lasers (QCLs) using a two-dimensional heat dissipation model. The temperature distribution, heat flow, and thermal conductance (G(th)) of QCLs were obtained through the thermal simulation. A thick electroplated Au around the laser ridges helps to improve the heat dissipation from devices, being good enough to substitute the buried heterostructure (BH) by InP regrowth for epilayer-up bonded lasers. The effects of the device geometry (i.e., ridge width and cavity length) on the G(th) of QCLs were investigated. With 5 mu m thick electroplated Au, the G(th) is increased with the decrease of ridge width, indicating an improvement from G(th) = 177 W/K.cm(2) at W = 40 mu m to G(th) = 301 W/K.cm(2) at W = 9 mu m for 2 mm long lasers. For the 9 mu m x 2 mm epilayer-down bonded laser with 5 mu m thick electroplated Au, the use of InP contact layer leads to a further improvement of 13% in G(th), and it was totally raised by 45% corresponding to 436 W/K.cm(2) compared to the epilayer-up bonded laser with InGaAs contact layer. It is found that the epilayer-down bonded 9 mu m wide BH laser with InP contact layer leads to the highest G(th) = 449 W/K.cm(2). The theoretical results were also compared with available obtained experimentally data.