Modelling output admittance frequency dispersion in AlGaN/GaN MODFETs

Output admittance frequency dispersion in MODFETs and MESFETs is known to be caused by the interaction of carriers with traps in the active regions of the device. For MODFETs in saturation, this dispersion is often shifted in frequency and broader than expected for a discrete trap. Frequency dispersion can be significant for devices operated in saturation, where the non-uniform electric field in the device win cause a distribution of emission rates from traps, arising from a field-induced distribution of thermal activation energies. In this work, a Gaussian function is used to allow a simple demonstration of the effect of the electric field on frequency dispersion characteristics. The model provides an excellent description of the shift and broadening of measured output susceptance frequency dispersion of Al_0.25Ga_0.75N/GaN MODFETs, and provides further insight into characteristics of the traps responsible for the frequency dispersion.