In this study, gallium nitride (GaN)-based metal-insulator-semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with a gallium oxide (GaO(x)) gate layer formed by alternating current bias-assisted photoelectrochemical oxidation of n-GaN are presented. By introducing the GaO(x) gate layer to the GaN MIS UV PDs, the leakage current is reduced and a much larger UV-to-visible rejection ratio (R(UV/vis)) of spectral responsivity is achieved. In addition, a bias-dependent spectral response results in marked increase of the R(UV/vis) with bias voltage up to ~10(5). The bias-dependent responsivity suggests the possible existence of internal gain in of the GaN MIS PDs.

In this study, gallium nitride ͑GaN͒-based metal-oxide-semiconductor diodes with a gallium oxide ͑GaO x ͒ gate layer formed by ac bias-assisted photoelectrochemical oxidation of n-type GaN in H 2 O were demonstrated. A typical flatband voltage of 4.35 V was obtained by capacitance-voltage ͑C-V͒ measurement. The observed C-V curves shifted toward the negative voltage side when the GaO x /n-GaN heterostructures were annealed in ambient oxygen ͑O 2 ͒. This result could be tentatively attributed to the fact that the negative effective charges existing in the GaO x layer and/or in the n-GaN/GaO x interface could be reduced due to the ambient O 2 annealing process. A negative value of the effective charge density of ϳ2.01 ϫ 10 −7 C/cm −2 , which corresponds to an effective insulator charge number density of around 1.25 ϫ 10 12 cm −2 , was obtained.Due to their rapid development, gallium nitride ͑GaN͒-based semiconductor materials have been extensively applied to optoelectronic devices such as light emitting diodes, laser diodes, and photodetectors. 1 Due to the tremendous success of commercialized GaN-based emitters and their outstanding potential in high power, high temperature, and high speed applications caused by the wide bandgap of the nitride-based semiconductors, more studies need to be conducted on GaN-based electronic devices, such as bipolar transistors and field effect transistors. 2 Although metal-semiconductor field effect transistors ͑MESFETs͒ have been commercially produced, 3 progress in the development of metal-oxidesemiconductor field effect transistors ͑MOSFETs͒ is still limited compared with that of MESFETs due to the lack of low cost and high performance GaN-based metal-oxide-semiconductor ͑MOS͒ diodes and capacitors. The high quality Schottky contacts and gate oxides on GaN are the key components of high performance MESFETs and MOSFETs, respectively. 4-6 The Schottky contacts on GaN-based semiconductors have been well-studied and applied to GaN-based MESFET in the past decade. 4,7 Although dielectrics such as SiO on GaN have been studied, GaN-based MOS structures show no clear sign of strong inversion. 8-10 The gate dielectric layers in GaN-based MOS structures can be prepared by physical vapor deposition, thermal oxidation, or chemical vapor deposition. In this study, the gate dielectric oxide of gallium oxide ͑GaO x ͒ was grown on n-GaN epitaxial layers by ac bias-assisted photoelectrochemical ͑PEC͒ oxidation of n-GaN in H 2 O. This approach for the formation of GaO x layers is different from the conventional PEC method, which has a low growth rate and uses diluted phosphorus acid ͑H 3 PO 4 ͒ and alkaline solutions. 11 The ac bias-assisted PEC oxidation features a low temperature process and a high growth rate to form the GaO x layer on GaN epitaxial layers. 12 In this paper, the characterization of GaN-based MOS structures with a GaO x gate layer formed by ac bias-assisted PEC oxidation was discussed.The GaN wafers used in this study were grown on c-face ͑0001͒ sapphire ͑Al 2 O 3 ͒ substrates i...