InGaN/GaN Multiquantum-Well Metal-Semiconductor-Metal Photodetectors With Beta- ${\rm Ga}_{2}{\rm O}_{3}$ Cap Layers

InGaN/GaN multiquantum-well (MQW) metal-semiconductor-metal photodetectors with a beta-Ga₂O₃ cap layer formed by the furnace oxidation of a GaN epitaxial layer are fabricated and characterized. The beta-Ga₂O₃ cap layer is found to suppress the reverse leakage current by at least about two orders of magnitude with a 5-V applied bias because it creates a thicker and higher potential barrier. The reverse leakage current can be further reduced and a 90-fold larger ultraviolet-to-visible rejection ratio can be achieved by using InGaN/GaN MQW layers, which confine the electron-hole pairs generated by lower-energy photons. In addition, the noise level is reduced and detectivity is increased. With a 5-V applied bias, the noise-equivalent power and normalized detectivity are 8.4 × 10^-13 W and 7.9 × 10¹² Hz^0.5 W^-1, respectively.