Impact of plasma pre-treatment before SiNx passivation on AlGaN/GaN HFETs electrical traps

The authors report on the effects of plasma pre-treatment before SiNx passivation on the electrical traps of undoped AlGaN/GaN HFETs. Different plasmas were tested with O2 or CF4 or (O2 + CF4) gas. The maximum drain current decreased when an O2 plasma was used before SiNx passivation, and increased up to 35% in the other cases. The best results were obtained using an (O2 + CF4) plasma. In that case, an important decrease of the knee voltage was observed in the Ids(Vds, Vgs) characteristic which becomes independent of the bias variation. The influence of the lighting on the electrical characteristics of AlGaN/GaN HFETs was also studied. We have deduced that a part of the electrical traps is located at the surface of the structure and that another part is present under the gate, in the volume of the AlGaN layer, and/or at the interface AlGaN/GaN.