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.仅以电子作为有源载流子的单载流子传输光电二极管（Uni-traveling-carrier photodiodes, UTC-PDs）凭借高饱和功率、宽带宽等独特性能，已成为高速光电子学领域不可或缺的核心器件。然而，由于缺乏兼具合适能带对齐与晶格匹配特性的宽带隙III-V族半导体组合，将其工作波长拓展至可见光区域以拓展应用场景仍极具挑战。本研究表明，基于范德瓦尔斯异质结的UTC-PD可解决这一难题：该异质结以二维过渡金属硫族化合物二硫化钼（molybdenum disulfide, MoS₂）作为光吸收层，以氮化镓（gallium nitride, GaN）薄膜作为载流子收集层。通过在GaN薄膜上直接外延生长MoS₂层，可实现异质界面间高效快速的垂直载流子传输。测试结果显示，本器件展现出吉赫兹量级的频率响应，且在整个可见光光谱范围内量子效率约为1%，凸显了其在高速可见光光电子学领域的应用前景。