High Responsivity, Low Dark Current Ultraviolet Photodetectors Based on Two-Dimensional Electron Gas Interdigitated Transducers

An ultraviolet (UV) photodetector employing the two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface as an interdigitated transducer (IDT) is characterized under optical stimulus. The 2DEG-IDT photodetector exhibits a record high normalized photocurrent-to-dark current ratio of 6 x 10(14). We also observe a high responsivity (7800 A/W) and ultraviolet-visible rejection ratio (10(6)), among the highest reported values for any GaN photodetector architecture. We argue that the valence band offset in the AlGaN/GaN heterostructure is essential in achieving this high responsivity, allowing for large gains without necessitating the presence of trap states. Our proposed gain mechanism is consistent with measurements of the scaling of gain with device channel width and incident power. The photodetector architecture has a simple two-step fabrication process, compatible with AlGaN/GaN high electron mobility transistor (HEMT) processing. This unique combination of low dark current, high responsivity, and simple fabrication is attractive for a variety of UV sensing applications.