Influence of the polarization on interfacial properties in Al/SiO2/GaN/Al0.4Ga0.6N/GaN heterojunction metal–insulator–semiconductor structures

Abstract

GaN-based metal–insulator–semiconductor (MIS) structures were fabricated by depositing a ${\mathrm{SiO}}_2$ film on a metalorganic chemical vapor deposition-grown $\mathrm{GaN}/{\mathrm{Al}}_{\text{0.4}}{\mathrm{Ga}}_{\text{0.6}}\mathrm{N}/\mathrm{GaN}$ double heterojunction. Various-frequency capacitance–voltage $\mathrm{(C-V)}$ measurements were carried out on the MIS structures. The measured $\mathrm{C-V}$ curves show a notable flatband shift of up to about 12.5 V with a typical polarization hysteresis window (9.4 V in width). Moreover, the capacitance of the heterojunction MIS structure reaches a minimum value under 4.1 V bias (forward scan) or −6.5 V bias (reverse scan). Due to the strong polarization and piezoelectric effects existing in AlGaN/GaN heterostructures, these results are deemed to be due to the influence of the piezoelectricity and polarization effects in the structure. Conductance–voltage $\mathrm{(G-V)}$ measurements were also performed. Various-frequency $\mathrm{C-V}$ and the $\mathrm{G-V}$ behaviors indicate that interface states have little influence on the sample.