SUMMARY
The development of AlGaN/GaN high electron mobility transistors (HEMTs) has shown much promise for advancing future RF and microwave communication systems. In addition, it is being developed for military radars, advanced wireless schemes, and power electronics for smart grid and hybrid electric vehicles. However, their implementation in these applications carries concern over device reliability. Part of this concern is over mechanical stresses induced in the devices as well as the temperature rise in the devices which limits device performance. In both cases, the combination of stress and temperature must be measured and verified experimentally. In this work, we utilize optical characterization techniques (micro-Raman spectroscopy and micro-Photoluminescence) to measure temperature and various mechanical stresses, namely, residual stress, inverse piezoelectric stress, and operational thermoelastic stress in state-of-the-art AlGaN/GaN HEMTs. Through the use of these methods, for the first time, we have mapped the vertical and lateral stress distributions as well as the temperature distribution in these devices. Results show that stress can be influenced by the substrate as well as the device electrode metallization. Also it is observed that bias conditions alter the heat generation profile across the conductive channel. By monitoring stress and temperature related phenomena in these devices, it is possible to link these parameters to device degradation as a function of bias conditions and electrical stress testing. These measurements reveal an unprecedented relationship between temperature/stress, and device performance/reliability as a result of the implementation of these two optical characterization methods.