Investigation Of Thermal Issues In GaN-based High Electron Mobility Transistor

As the third-generation semiconductor, AlGaN/GaN high electron mobility transistors (HEMTs) has a very widely application prospects in high-temperature and high-power applications due to its high breakdown voltage, thermal conductance and saturation velocity. With the reduction of the device dimensions, the device performance becomes deteriorated at high temperature, so the paper will focus on the thermal issues of GaN based HEMTs.Firstly, high-temperature characteristics of AlGaN/GaN HEMTs including Ohmic contact, Schottky contact, DC and C-V characteristics are investigated systematically, Then the thesis puts emphasis on the temperature dependent current-voltage measurement of Schottky contact from 300K-473K. The ideality factor and barrier height determined based on the thermionic emission theory are found to be strong functions of temperature. The current transport mechanisms are discussed through numerical fitting considering the temperature dependent series resistance. For the forward I-V curves, it is found that tunneling dominates at room temperature while the thermionic emission becomes more significant with increased temperature.Two DC electrical methods developed by McAlister and Kuzmik are employed to test the channel temperature of the device. In the case of variable temperatures, the channel temperature of the device was obtained by monitoring DC electrical temperature sensitive parameters, such as DC drain-source current, source resistance and threshold voltage. Electrical methods are noninvasive and fast, and this can be used to estimate the self-heating of GaN based HEMT.AlGaN/GaN HEMTs are simulated by Silvaco-ATLAS, and it is found that the highest electric field and temperature locate at the drain side of the gate edge. Meanwhile, the three-dimensional finite-element model is constructed to obtain the temperature distribution of GaN based HEMTs, and this model takes the nonlinear relationship of material thermal conductivity with temperature and the convection heat transfer coefficient into account. Then, comparing the simulation results with the results of two dc electrical methods, it is found that they have the same tendency and there is a small divergence. It is indicated that the simulation method is an easier and more convenient method to provide the thermal management of the GaN-based HEMTs.