Model Of Algan/gan Hemt Devices And The Thermal Effect Research

As the third generation semiconductor material, GaN takes advantages form bigger forbidden band width, higher breakdown voltage, higher thermal conductivity and higher electronic saturation speed which are suitable for high temperature power applications. As a promising candidate for power application, AlGaN/GaN HEMT (high electronic mobility transistor) has been investigated intensively, however, the causes of high temperature degradation are still not clear. This paper investigates the AlGaN/GaN HEMT degradation causes at elevated temperatures by means of tests and simulations.Firstly, this paper introduces the working principle of AlGaN/GaN HEMT, measures the current-voltage (I-V) characteristics in the temperature range of25℃-200℃, and analyzes the thermal failure mechanisms of the device. It shows that with increasing temperature, the maximum output saturated current decreases by17%and the maximum trans-conductance drops by26.7%. The further study of two dimensional electron gas (2DEG) indicated that the mobility of2DEG decreases quickly at elevated temperatures, and it is the main factor for the thermal failure of the device.Secondly, the Ⅰ-Ⅴ characteristic of of Schottky contact is measured and the thermal failure mechanism is detailed studied. Several current-transport mechanisms were analyzed to separate the current component, and results show that multi-step tunneling current is the main component in the forward Schottky current, and the dislocation density, according to a model of tunneling along the dislocation line, gives the value of1.88×107cm-2. The reverse Schottky leakage current can be described by Frenkel-Poole model, and further analysis indicates a trap state located0.27eV below AlGaN conduction band to assist electron tunnel. Through C-V measurement, the heteroj unction interface state density was extracted to study the trap effect, results show that with the increasing temperature, no new trap is produced, but the original trap activity is improved which can deteriorate the device characteristics.Finally, the three dimension (3D) thermal analysis is conducted to study the thermal behavior of multi-finger AlGaN/GaN HEMT, the impact of structure parameters on the channel temperature is studied, and thermal optimization design process is proposed. It is suggested that SiC should be chosen as the substrate. The channel temperature increases linearly with substrate thickness and gate fingers while decreases with finger pitch. The thermal analysis of AlGaN/GaN HEMT with variational gate pitch is conducted to finish the optimization design.