Physics Based Frequency Dispersion Model of GaN MESFETs

摘要

A physics based model for GaN MESFETs is developed to determine the frequency dispersion of output resistance and transconductance due to traps. The equivalent circuit parameters are obtained by considering the physical mechanisms for current collapse and the associated trap dynamics. Detrapping time extracted from drain-lag measurements are 1.55 seconds and 58.42 seconds indicating trap levels at 0.69eV and 0.79eV, respectively. The dispersion frequency is in the range of MMz at elevated temperature, where a typical GaN power device may operate, although at room temperature it may be few Hz. For a 1.5 micrometers. 150 micrometers GaN MESFET with drain and gate biases of 10V and -5V respectively, 5% decrease in transconductance and 62% decrease in output resistance at RF frequencies from their DC values are observed. The dispersion characteristics are found to be bias dependent. A significant decrease in transconductance is observed when the device operates in the region where detrapping is significant. As gate bias approaches toward cutoff, the difference between output resistance at DC and that at RF increases. For drain and gate biases of 10V and -5V, output resistance decreases from 60.2 k. at DC to 7.5 k. at RF for a 1.5 micrometers. 150 micrometers GaN MESFET. This article was published in IEEE Transactions on Electron Devices, Vol. 51, No. 6, pp. 846-853, June 2004.