Investigation Of Temperature-dependent Properties Of GaN-based High Electron Mobility Transistor

Due to the many outstanding material properties of GaN, such as high breakdown electric field, high sheet carrier density and high electronmobility, the Al GaN/GaN HEMTs havebeen widely used in the high power and high frequency applications. One of the greatest impediments affecting the further development of Al GaN/GaN HEMTs is the temperaturereliability, so the study of temperature reliability is very essential and necessary to improve the properties of the devices. On the basis of this research background, the paper will mainly focus on the temperature properties of the GaN device especially in the cryogenic temperature.The temperature properties have been simulated by using Silvaco software. Firstly, the models and numerical computation methods are introduced, and then we make a comparision of the conduction band of the devices with different instructures. Electric field and thermal distribution in the different temperature are obtained, it is found that the electric field will decrease with the temperature rises. Lattice temperature have been extracted at the temperature between 150 K and 450 K, the hot spot of the device is found primarily located in the submicro region which near the end of the gate closed to the drain. For further explanation, a series of measures are proposed to reduce the junction temperature and self-heating effect. Then, the output and transfer characteristics are simulated at the temperature between 77 K and 200 K, it is found that the saturated output current and the peak transconductance increase with the temperature drops. The threshold voltage can be extracted from the transconductance curve.Because of the fact that the threshold voltage mainly depends on the sheet carrier density of the two-dimensional electron gas, at the temperature between the 50 K to 500 K, 1D Possion software is used to simulate the sheet carrier density and the difference between the conduction band of the Al GaN and GaN. It is found that the quantity of electrons increases with the temperature falls. Besides, the dependence of the Al component and the thickness of the barrier layer on the sheet carrier density are also analysed in this paper.The DC features have been tested at the cryogenic temperatures between 77 K and 270 K, the output and transfer characteristics are tested and analysed respectively. The conclusions we obtained are coinside with the simulation. The dependence of the electronic mobility on the temperature is tested by using TLM method, it is found that the electronic mobility is increasing with the temperature decreases. The scattering mechanisms which influence the electronic mobility are explained as well. Capacitance-Voltage characteristics in different temperatures and properties of traps are also discussed in this paper by using DLTS(Deep Level Transient Spectroscopy). An abnormal phenomenon arises that the threshold voltage drifts positively with the temperature decreases.We think it can probably attribute to the influence of the traps which are in the interface between the Al GaN and GaN. Traps in the Al GaN/GaN device have also been studied by Arrenius analysis. The types, the energy level and capture cross section have been obtained through some numerical operations.The mechanism of both reverse and forward gate leakage current in Al GaN/GaN device have been studied at temperature ranging from 400 K to 120 K. The ideality factor and the Schottky barrier height are extracted by using thermionic emission model. Below 200 K, leakage current is nearly independent of temperature, indicating that conduction is dominated mainly by FN(Fowler-Nordheim) tunneling mechanism at low temperature. The mechanism of reverse gate leakage current has been analyzed by using FN model and FP(Frenkel-Poole) emission model respectively. The dielectric permittivity at high frequency and the barrier height for electron emission from trap state are extracted and consistent with the relevant reports.