High responsivity, low dark current ultraviolet photodetector based on AlGaN/GaN interdigitated transducer.

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 (NPDR, $6times10^{14}$). In addition, we observe a high responsivity ($7,800$ A/W) and ultraviolet-visible rejection-ratio ($10^{6}$), among the highest reported values for any GaN photodetector architecture. We propose a gain mechanism to explain the high responsivity of this device architecture, which corresponds to an internal gain of $26,000$. 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, in contrast to common metal-semiconductor-metal (MSM) photodetector architectures. Our proposed gain mechanism is consistent with measurements of the scaling of gain with device channel width and incident power. In addition to high performance, this photodetector architecture has a simple two-step fabrication flow that is monolithically compatible with AlGaN/GaN high electron mobility transistor (HEMT) processing. This unique combination of low dark current, high responsivity and compatibility with HEMT processing is attractive for a variety of UV sensing applications.