Effect of p-doped overlayer thickness on RF-dispersion in GaN junction FETs

Successive reactive ion etchings (RIE) were performed on the access regions of p/sup +/-n GaN JFETs. A decrease in the n-layer sheet resistance, with a consequent increase in I/sub DSS/ was detected after complete removal of the p-layer, due to a reduction in the n-layer depletion region. An increase in RF-dispersion was experienced, as a result of the progressive reduction of screening from surface-states originally provided by the overlying p-cap layer. No dispersion was detected before cap removal. A continuous increase in f/sub t/ and f/sub max/ was detected even before complete removal of the p-layer, due to virtual gate length reduction. It is expected that an optimized p-doped overlayer will provide current slump suppression without degradation in cutoff frequency or breakdown.