Thermal boundary resistance between GaAs and p-side metal as limit to high power diode lasers

Abstract

Studies are presented on the anomalously high thermal boundary resistance observed in efficient high power diode lasers between the p-side contact and metal submount. This barrier is responsible for a thermal resistance of around 1 K/W (around 40% of total) and its elimination would significantly improve the beam quality and power in high power devices. First, we show that no barrier is observed on the n-side even up to high CW heat flux levels (to $\sim 2$ kW/cm$^{\mathbf {2}}$), confirming a p-side effect. Second, a 10-fold variation in the thermal conductivity of the submount material (from CuW to CVD diamond) is shown to have minimal impact on the measured thermal barrier, thermal resistance and curvature in the thermal lens, confirming a chip-internal effect. The measured variation in thermal lens was reproduced in simulation only when a boundary resistance was included. These results are further evidence that the thermal boundary resistance is related to material limits on heat transport out of the p-side of the devices.