Photogating-enhanced photodetection in substrate-assisted borophene-graphene hybrids

We investigate the performance and photoresponse mechanisms in hydrogenated borophene (borophene)-based photoconductor (PC)-type hybrid photodetectors (PDs) and the effect of substrates, with and without photogating (PG) assistance, on these PDs. Photoconductive (PC) effects involve direct modulation of channel conductivity by photogenerated carriers, while photogating (PG) effects involve indirect photocurrent modulation via trapped charges across an interface, acting as a local gate. Graphene on a SiO₂/Si substrate generates photocurrent primarily through the PG effect. The use of an insulating polydimethylsiloxane (PDMS) substrate suppresses the PG and hence the photocurrent in the graphene/PDMS PD. The champion device with the additional borophene on the graphene/SiO₂/Si PD exhibits enhanced photocurrent due to the combined PC and PG effects. Absorption and photocarrier transfer from borophene to graphene control the PC, and the PG assists the increased graphene channel carrier density and transport. This champion device achieves a responsivity of 7.88 × 10³ A W^-1, a normalized gain of 0.30 cm² V^-1, and a detectivity of 1.74 × 10¹⁴ Jones (under 532 nm illumination, 1 V, 0.02 mW cm^-2), outperforming the graphene/SiO₂/Si PD. The limited photocurrent in the borophene/graphene/PDMS PD underlines the absence of the PG effect on the PDMS substrate. Using high mobility charge transporter graphene resulted in a faster response time (τ_rise = 91 ms, τ_fall = 93 ms) in the borophene/graphene/SiO₂/Si PD.