Positive Threshold-Voltage Shift of Y_2O_3 Gate Dielectric InAlN/GaN-on-Si (111) MOSHEMTs with Respect to HEMTs

摘要

The electrical characteristics of In_(0.18)Al_(0.82)N/GaN MOSHEMTs-on-Si (111) with Y_2O_3 gate dielectric of thickness between 5to 30 nm are reported. A positive shift in threshold voltage, V_(th), with respect to Schotfky gate HEMTs is observed, which is in contrast to that for ZrO_2 gate dielectric MOSHEMTs. An analytical V_(th), model is proposed to quantify the fixed oxide charges at the Y_2O_3/In_(0.18)Al_(0.82)N interface (n_(ox,intf)) and in the Y_2O_3 bulk (n_(ox,bulk)- The negative polarity of the fixed oxide charges (n_(ox,intf), n_(ox,bulk) is believed to be the reason for the abovementioned positive V_(th) shift. X-ray photoelectron spectroscopy analysis reveals that a thin interfacial layer (IL) may have formed as a result of spontaneous reaction between dielectric Y_2O_3 and In_(0.18)Al_(0.82)N/GaN heterostracture, leaving Y_2O_3 bulk on top for thick dielectric film. We believe n_(ox,intf)is located in the IL and that its polarity and magnitude are related to the constituents of the IL, which comprise mainly YAlO_xN_y and its sub-oxynitrides. It is also observed that Y_2O_3 bulk has negative fixed charges (n_(ox,bulk) with a magnitude that depends on film densification upon thermal annealing treatment.