Effects of reactive ion etching on the electrical characteristics of GaN

We present an investigation of the electrical characteristics of plasma exposed GaN. The specific contact resistance of ohmic contacts fabricated on GaN after argon plasma bombardment for 2.5 min at 0.03 W/cm2 are measured to decrease by a factor of 4 compared to the unetched surface. Gold has been found to be the best material for GaN Schottky diode. A study of the electrical performance of diodes fabricated on plasma exposed GaN has been undertaken. To compare the effect of the chemical versus physical factors, as well as the role played by the ion mass of the etchant species during the etching process on diode behavior, GaN surfaces have been exposed to Ar, N2, as well as SF6+N2 plasmas before diode fabrication. Our data indicate that a plasma with low ion mass etchant species or a dominant chemical mechanism of etching with a high etch rate creates less surface damage. The use of a SF6+N2 plasma should be possible for GaN transistor gate recessing.