Layered Heterostructures Based on MoS₂/MoSe₂ Nanosheets Deposited on GaN Substrates for Photodetector Applications

Due to the advanced properties of layered 2D materials, their heterostructuring with conventional 3D semiconductors is one of the promising ways to design efficient and affordable optoelectronic devices. However, systematic studies on designing 2D/3D heterojunctions with a focus on enhancing the photodetection properties are sparse in the literature. In this report, we present systematic experimental and theoretical investigations on 2D MoS2/MoSe2 heterostructuring with modified GaN substrates for designing efficient photodetectors. We achieved a gradual increment in photocurrent by engineering MoS2 and MoSe2 as single/double heterojunctions on GaN substrates. Time-correlated single-photon counting (TCSPC) results infer significant improvement in the lifetimes of the photoexcited charge carriers for the optimized MoS2/MoSe2/e-GaN heterostructure-based photodetectors. Interestingly, photodetectors designed with double heterojunctions that maintain type-II band alignment (e-GaN/MoSe2/MoS2) exhibit the highest photoresponsivity of 82 A/W, specific detectivity of 1.79 ×1014 Jones, external quantum efficiency of 27,880%, and stability for over 6 months in a laboratory testing environment under the illumination of 365 nm. Density functional theory (DFT) simulations establish the superiority of double heterojunctions with staircase band alignment for efficient charge carrier transport. This study provides fundamental insights on optimizing the band alignment for desired photodetection concerning 2D/3D integration, which can be exploited for other hybrid integrated systems and applications.