Resonant Tunneling Due to van der Waals Quantum-Well States of Few-Layer WSe₂ in WSe₂/h-BN/p⁺-MoS₂ Junction

Few-layer transition metal dichalcogenides (TMDs) exhibit out-of-plane wave function confinement with subband quantization. This phenomenon is totally absent in monolayer crystals and is regarded as resulting from a naturally existing van der Waals quantum-well state. Because the energy separation between the subbands corresponds to the infrared wavelength range, few-layer TMDs are attractive for their potential to facilitate the application of TMD semiconductors as infrared photodetectors and emitters. Here, we report a few-layer WSe₂/h-BN tunnel barrier/multilayer p⁺-MoS₂ tunnel junction to access the quantized subbands of few-layer WSe₂ via tunneling spectroscopy measurements. Resonant tunneling and a negative differential resistance were observed when the top of the valence band Γ-point of p⁺-MoS₂ was energetically aligned with one of the empty subbands at the Γ-point of few-layer WSe₂. These results demonstrate a critical step toward the utilization of subband quantization in few-layer TMD materials for infrared optoelectronics applications.