Research And Analysis Of GaN MOSFET Characteristics In The Method Of Computer Simulation

The Gallium Nitride (GaN) and its related MOSFET device have been attracting attention because of its ability to operate at high power, high temperature, and high speed. Deep researches on n-channel GaN MOSFET begin since 2004, and the crucial factors affect its development are difficulty in obtaining p-doped substrate and the quality of insulator/GaN interface. This thesis basing on the consideration of mobility related with doping concentration and interface state model, discusses the characteristics of GaN MOSFET using the method of computer simulation. By modifying the physical models of GaN material and calculating in the environment of new generation TCAD tool Sentaurus software, we conclude as follows:(1) The material parameters of GaN as bandgap and permittivity have been corrected. Physical models as recombination and incompleted ionization have been ameliorated. New expressions for GaN mobility models have been obtained by Curvefitting.(2) Modified physical models have been proved to be correct with comparison of DC experiment data. Relationship between device structures and DC performance shows 0.7μm is the crucial point of short-channel effect; the threshold voltage and output current can reach 1V and 0.7mA/μm. We also obtain the transconductance 26mS/mm at Vds=4V.(3) Simulation results show consistency with experiment at high temperature. When temperature varies from 300K to 800K, the DC characteristics of device worsen. We conclude the decay of mobility and saturation drift velocity is the main reason. With temperature elevating, the saturation drain current and transconductance drop 50% and 58% respectively. However at 800K saturation drain current and transconductance can even reach 0.39mA/μm and 10mS/mm, and the ZTC point is predicted to be 1.4V.(4) Small signal analysis of GaN MOSFET with different device structures shows the cut-off frequency can reach 38.2GHz. The crucial factor of device high frequency performance is mobility in GaN. With mobility as high as 1000cm²V^-1s^-1, the cut-off frequency of GaN MOSFET can be predicted to be 180GHz.