Low-temperature atomic layer deposition-grown Al2O3 gate dielectric for GaN/AlGaN/GaN MOS HEMTs: Impact of deposition conditions on interface state density

The oxide/semiconductor interface state density (Dit) in Al2O3/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with gate oxides grown by atomic layer deposition at low deposition temperature is analyzed in this work. MOS-HEMT structures with Al2O3 gate oxide were deposited at 100 and 300 degrees C using trimethylaluminum precursor and H2O and O-3 oxidation agents. The structures were found to show negative net charge at oxide/barrier interface with density (N-int) of 10(13) cm(-2), which was attributed to the reduction of barrier surface donor density (NDS). Dit was determined using capacitance transient techniques, and the results were assessed by the simulations of the capacitance-voltage characteristics affected by interface traps. The results indicate a lower interface quality of the sample with Al2O3 grown using O-3 agent compared to those with H2O, even though the former provided lowest gate leakage among the analyzed structures. Moreover, to uncover the NDS nature, Dit distributions determined here were compared to that reported previously on devices with Nint close to zero, i.e., with fully compensated surface barrier polarization charge by NDS [Tapajna et al., J. Appl. Phys. 116, 104501 (2014)]. No clear correlation between Dit and NDS was concluded, indicating the nature of NDS to be different from that of interface states in the energy range analyzed here. (C) 2016 American Vacuum Society.