Analysis of field-plate effects on buffer-related lag phenomena and current collapse in GaN MESFETs and AlGaN/GaN HEMTs

A two-dimensional transient analysis of field-plate GaN MESFETs and AlGaN/GaN HEMTs is performed in which a deep donor and a deep acceptor are considered in a semi-insulating buffer layer, and quasi-pulsed current-voltage curves are derived from them. How the existence of a field plate affects buffer-related drain lag, gate lag and current collapse is studied. It is shown that in both MESFET and HEMT, the drain lag is reduced by introducing a field plate because electron injection into the buffer layer is weakened by it, and the buffer-trapping effects are reduced. It is also shown that the field plate could reduce buffer-related current collapse and gate lag in the FETs. The dependence of lag phenomena and current collapse on the field-plate length and on the SiN passivation layer thickness is also studied. The work suggests that in the field-plate structures, there is an optimum thickness of the SiN layer to minimize the buffer-related current collapse and drain lag in GaN MESFETs and AlGaN/GaN HEMTs.