Investigation of temperature distribution on the facet of the device, with high spatial and temperature resolution, is crucial to gain insight into thermally activated degradation modes in GaN-based lasers. This work undertakes the problem of temperature distribution measurement on the facet of the nitride lasers.
Thermal investigation of the nitride devices is mainly based on thermal imaging. However, this approach is characterized by inherently low spatial resolution, as well as the fact, that the registered image, is averaged over the volume of the device, limiting the ability to observe the enhanced thermal processes occurring at the vicinity of the surface (front facet). Thermoreflectance spectroscopy, provides the possibility of registering of high spatial and temperature resolution images of the surface of the device operating in quasi-CW or pulsed mode.
In this work we present development of the unique experimental setup and procedure, devoted to the thermal characterization of the nitride lasers. Thermal characterization of series of devices was performed, providing a mode for comparing different operating conditions, geometries and device designs. Measurement of the temperature profile and high-resolution temperature distribution maps on the front facet of AlGaN/GaN via thermoreflectance spectroscopy will be demonstrated. The results indicate the direction to take in order to improve the laser reliability and performance. Additionally, the degradation mechanisms induced by temperature increase are discussed.