Terahertz spectroscopy of thermal radiation from AlGaN/GaN heterostructure on sapphire at low temperatures

Abstract

Terahertz spectroscopy of thermal radiation from electrically pumped AlGaN/GaN structures on sapphire substrate was investigated in this work. Comparison of experimental THz spectroscopy results to theoretical spectra calculations shows that thermal radiation of the sample lattice is the main mechanism causing the emission above T = 155 K, and it is mainly influenced by sapphire substrate. Here, the emission was attributed to the radiative electron transitions in shallow impurities and nitrogen vacancies as well as to radiative decay of longitudinal optical phonons (387 cm-1) in sapphire substrate. We have successfully demonstrated that THz emission spectroscopy can be used to define the temperature at which thermal emission from AlGaN/GaN HEMT structures dominates the emission spectrum.