Interface characterization of Al_2O_3/AlGaN structures prepared by atomic layer deposition

摘要

We have investigated interface properties of Al_2O_3/GaN and Al_2O_3/AlGaN/GaN structures that are promising for realizing MOSFETs and improving operation stability of HEMTs. An Al_2O_3 layer was deposited on n-GaN and AlGaN/ GaN heterostructure samples by atomic layer deposition (ALD) using TMA and H_2O as precursors. The bandgap of Al_2O_3 was estimated to be 6.7 eV from the X-ray photoelectron spectroscopy analysis. The capacitance-voltage (C-V) measurement was carried out on the MIS structures. After the post-deposition annealing at 400 ℃, we observed the C-V curve close to the ideal one in the Al_2O_3-GaN structure. We also observed systematic decreases in accumulation capacitance and threshold voltage in the C-V curves in the Al_2O_3/AlGaN/GaN structure, with increasing the thickness of the Al_2O_3 layer. From the difference between experimental and calculated values of the threshold voltage, the density of electronic state at the Al_2O_3/AlGaN interface was estimated to be ～5×10~(12) cm~2 eV~(-1) or less. These results indicate ALD-Al_2O_3 is promising for an insulator for a gate structure and a surface stabilizing layer in AlGaN/GaN HEMTs.