Broadband InSe/MoS₂ Type-II Heterojunction Photodetector with Gate-Tunable Polarity Induced Near-Linear Wavelength-Dependent Photocurrent Peak

Selectable polarity in van der Waals materials not only broadens the scope of design for electronic components but also opens new avenues for the development of advanced electronic, optoelectronic, and sensor devices. In this study, we fabricated vertically stacked InSe/MoS₂ van der Waals type-II heterojunction photodetectors and conducted a systematic investigation of their photoelectrical properties. Our findings demonstrate the high performance of these photodetectors, characterized by effective suppression of charge recombination, the presence of both positive and negative photoconductivity under different incident light excitations, broad-spectrum detection ranging from 400 to 1064 nm, and remarkable responsivity and photodetectivity values of 10,200 A/W (-1430 A/W) and 3 × 10¹³ cm Hz^-1/2 W^-1 (3.6 × 10¹¹ cm Hz^-1/2 W^-1) at 532 nm (1064 nm), respectively. Additionally, the fabricated photodetectors exhibit a gate-tunable polarity transition at a gate voltage of -20 V, leading to a photocurrent peak, the position of which shows a near-linear dependence on the incident light wavelength. By applying external gate voltages, the van der Waals heterojunctions can flexibly switch between functions such as photodetection, modulation, and storage in different applications, providing new scope for the design of integrated circuits and the development of multifunctional devices. Through Poisson and drift-diffusion simulations, we attribute the observed negative photoresponse to electrons excited from the InSe valence band to the MoS₂ conduction band and subsequently trapped at the interface. The photocurrent peak arises from charge carrier accumulation at the interface, with its position determined by the interplay between the hole accumulation density in InSe and electron accumulation density in MoS₂. Our results present a promising opportunity for the design of compact spectrometers based on van der Waals type-II heterojunction photodetectors.