Metal-Semiconductor-Metal Photodiode Fabricated With an AlGaN/AlN Superlattice for UV Light Detection

Abstract We designed and fabricated a nonplanar metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD), incorporating a 30-pair Al0.5Ga0.5N/AlN superlattice (SL) absorption layer on a GaN on a sapphire substrate. In contrast to conventional PDs featuring a 100-nm-thick Al0.25Ga0.75N epilayer, our proposed PDs with the higher Al content of Al0.5Ga0.5N/AlN SLs did not exhibit degradation in epiwafer quality. Furthermore, we observed that the use of Al0.5Ga0.5N/AlN SLs resulted in a higher optical gain, specifically achieving voltage-dependent photoresponsivity in the MSM PDs. This improvement was observed with both the ohmic-type Ti/Al/Ni/Au (top) and the Schottky-type Ni/Au (bottom) electrodes, as well as with two Ni/Au Schottky metal electrodes. With the incorporation of Al0.5Ga0.5N/AlN SLs, our proposed MSM PDs with an Ohmic/Schottky-type electrode configuration showcased an enhanced photoresponsivity of 1129.8 A/W at ‒5 V in comparison to MSM PDs employing two Schottky-type electrodes. Moreover, by utilizing the Al0.5Ga0.5N/AlN SL absorption layer, we achieved an increased light current to dark current ratio, reaching 3.66 × 105 biasing at a ‒7 V. Following the implementation of our proposed MSM PDs with an Ohmic/Schottky-type electrode configuration, the gain ratio improvement underscores the efficacy of this approach. Subsequently, the fabricated device's transient response, demonstrating enhanced output performance, was analyzed using an in-house optical transmission setup. The estimated 3-dB cut-off frequency of this proposed MSM PD was found to be approximately 1.2 MHz.