Nearly lattice-matched molybdenum disulfide/gallium nitride heterostructure enabling high-performance phototransistors

Molybdenum disulfide (MoS2)-based phototransistors are attractive for optical electronics in a large-scale size, such as transparent touch screens. However, most of the work done over the past decade has been on an opaque SiO2/Si wafer with a small size (micrometer to millimeter). In this work, a large-scale multilayer MoS2-based phototransistor has been fabricated on a transparent freestanding gallium nitride (GaN) wafer using a scalable chemical vapor deposition method. Due to the near lattice match and small thermal expansion mismatch between GaN and MoS2, the as-grown multilayer MoS2-on-GaN film shows high material quality in terms of low full width at half-maximum (∼5.16  cm−1) for the E2g1 Raman mode and a high absorption coefficient (∼106  cm−1) in the wavelength range of 405–638 nm. Under a wavelength of 405 nm at an incident power of 2 mW and applied voltage of 9 V, the fabricated MoS2-on-GaN phototransistor achieved a maximum responsivity of 17.2 A/W, a photocurrent gain of 53.6, and an external quantum efficiency of 5289%, with specific detectivity (∼1010–1012 Jones) and low noise equivalent power (10−12–10−14  W/Hz1/2) in the visible range of 405–638 nm. A typical response time of 0.1–4 s in the ambient air has also been recorded for the demonstrated MoS2-on-GaN phototransistor. Our work paves a technologic stepping stone for MoS2-based phototransistors for multifunctional transparent and touch-based optoelectronics in the future.