Uni-traveling-carrier photodiode based on MoS2/GaN van der Waals heterojunction for high-speed visible-light detection

Uni-traveling-carrier photodiodes (UTC-PDs), which utilize only electrons as the active carriers, have become indispensable in high-speed optoelectronics due to their unique capabilities, such as high saturation power and broad bandwidth. However, extending the operating wavelengths into the visible region for wider applications is challenging due to the lack of suitable wide-bandgap III-V semiconductor combinations with the necessary band alignment and lattice matching. Here, we show that a UTC-PD based on a van der Waals heterojunction composed of a 2D transition metal dichalcogenide, molybdenum disulfide (MoS2), as a photoabsorption layer and a gallium nitride (GaN) film as a carrier collection layer, offers a solution to this challenge. The fast vertical carrier transport across the heterointerface is enabled by the direct epitaxial growth of a MoS2 layer on a GaN film. Our device demonstrates a frequency response in the several-GHz range with a quantum efficiency on the order of 1% throughout the entire visible spectrum, highlighting the promise for high-speed visible optoelectronics. Uni-traveling-carrier photodiodes (UTC-PDs) are well-established high-speed optoelectronic devices, but their adaptation to the visible range remains challenging. Here, the authors report the realization of UTC-PDs based on epitaxial van der Waals MoS2/GaN heterojunctions, showing frequency bandwidth of a few GHz across the visible spectrum.