A Weyl semimetal WTe₂/GaAs 2D/3D Schottky diode with high rectification ratio and unique photocurrent behavior

Since the discovery of Dirac semimetal graphene, two-dimensional (2D) Weyl semimetals (WSMs) have been widely used in low-energy photon detection, polarization imaging, and other systems due to their rich physical characteristics, such as unique nonlinear optical structure, topological nontrivial electronic structure, thickness-tunable bandgap, high electric conductivity, and so on. However, it is difficult to detect the photocurrent signal at room temperature because of its large intrinsic background current. Fortunately, the fabrication of a van der Waals (vdW) heterojunction based on WSM can effectively suppress the background current, greatly extend the detection range, improve the light absorption efficiency, and increase the response speed. Herein, the 2D type-II WSM 1T′-WTe₂/bulk GaAs vdW vertical Schottky diode is investigated. Benefiting from the lateral built-in electric field of 260 meV and zero-bandgap structure of 52 nm 1T′-WTe₂, it delivers a rectifying ratio over 10³ and can respond to the wavelength range of 400–1100 nm. Particularly, when the light power density is 0.02 mW/cm², the maximum photoresponsivity (R) and specific detectivity (D^*) under 808 nm are 298 mA/W and 1.70 × 10¹² Jones, respectively. Meanwhile, the I_light/I_dark ratio and response time are 10³ and 520/540 μs, respectively. Moreover, an abnormal negative response behavior can be observed with thin WTe₂ (11 nm) under 1064 nm illumination because of the open surface bandgap. It is suggested that such 2D WTe₂/GaAs mixed-dimensional vdW structure can be extended to other WSM/3D semiconductor junctions and used in fast response and wide broadband spectrum photodetectors' arrays.