Anisotropic photocurrent response at black phosphorus–MoS2 p–n heterojunctions

Abstract

We investigate the photocurrent generation mechanisms at a vertical p–n heterojunction between black phosphorus (BP) and molybdenum disulfide (MoS₂) flakes through polarization-, wavelength-, and gate-dependent scanning photocurrent measurements. When incident photon energy is above the direct band gap of MoS₂, the photocurrent response demonstrates a competitive effect between MoS₂ and BP in the junction region. In contrast, if the incident photon energy is below the band gap of MoS₂ but above the band gap of BP, the photocurrent response at the p–n junction exhibits the same polarization dependence as that at the BP–metal junction, which is nearly parallel to the MoS₂ channel. This result indicates that the photocurrent signals at the MoS₂–BP junction primarily result from the direct band gap transition in BP. These fundamental studies shed light on the knowledge of photocurrent generation mechanisms in vertical 2D semiconductor heterojunctions, offering a new way of engineering future two-dimensional materials based optoelectronic devices.