Temperature profile modelling and experimental investigation of thermal resistance of terahertz quantum-cascade lasers

Abstract

The authors perform a temperature profile modelling of a four-well resonant-phonon terahertz quantum-cascade laser (QCL) with a double-metal waveguide configuration by solving a steady-state heat transfer equation. The effects of ridge width and substrate thickness on the active region temperature are investigated. In addition, we also present two methods, i.e. light power-duty cycle measurement (method I) and threshold current-heat sink temperature measurement (method II), to investigate the thermal characteristics of the device. The two methods are briefly described. The extracted values of (normalized) thermal resistance from method I and method II are 11.7 K W−1 (4.9 K cm W−1) and 8.1 K W−1 (3.4 K cm W−1), respectively. The results show that method I is a valid and simple measurement especially for the thermal investigation of terahertz QCLs with relatively low continuous-wave (cw) operating temperatures. The measured results of method I are close to those from microprobe band-to-band photoluminescence measurements. Because of the lack of sampling points due to the relatively low cw operating temperature, method II shows a wide deviation from method I.