TCAD Analysis of GaN HEMT Output Conductance Through Trap Rate Equation Green's Functions

An efficient, in-house developed, TCAD simulator is used to investigate the effects of buffer traps in 150 nm gate length GaN HEMTs. The developed TCAD allows to compute not only the sensitivity of DC and AC Y parameters towards variations of the trap physical parameters, but also the local sensitivity, showing the device areas where traps influence most the HEMT behavior. The technique is applied to analyze the dependency of the output impedance (YDD) of a Fe-doped HEMT versus the buffer trap energy and concentration. We demonstrate that the two trap parameters impact differently on the output resistance in terms of frequency dispersion and of absolute values. The local source is also different, showing that buffer trap energy variations are also important when traps are located below the saturated channel, while trap concentration perturbations are important only for traps located under the ohmic portion of the channel.