Thickness Dependent HfO2 Interlayer Effects on Charge Transport and UV Photoresponse in α-Ga2O3 Photodetectors

This study investigates how nominal 5 and 10 nm HfO2 interlayers modify steady-state charge transport and ultraviolet photoresponse in α-Ga2O3-based deep-ultraviolet (DUV) photodetectors. A reference device without HfO2 and HfO2-interlayer devices were characterized under dark conditions and 270 nm UV-C illumination. The physical question addressed is whether these finite-thickness interlayers produce measurable changes in terminal carrier injection, voltage-dependent transport, and UV photoresponse under the same lateral geometry and measurement protocol. Under UV illumination, the 5 and 10 nm HfO2 devices exhibited sublinear power-law behavior in the positive-voltage branch with m = 0.699 and 0.580, respectively, whereas the negative-voltage branch showed m = 1.289 and 2.301. These exponents are used only as comparative descriptors because the nominally symmetric lateral structure was measured using a single sweep direction. HfO2 insertion enhanced the UV photoresponse, while its effect on dark current was non-monotonic. At −10 V, the 10 nm device showed the highest responsivity of 2.42 × 10−4 A/W, whereas at +20 V the 5 and 10 nm devices exhibited comparable responsivities of 2.94 × 10−4 and 2.84 × 10−4 A/W, respectively. Shot-noise-limited detectivity was estimated as a theoretical comparative metric. The results establish a controlled steady-state comparison of the three nominal interlayer conditions under the evaluated measurement conditions.