Highly Sensitive Ultraviolet Photodetector Based on an AlGaN/GaN HEMT with Graphene-On-p-GaN Mesa Structure

The advantageous role of 2D electron gas presence at the AlGaN/GaN interface attracts huge interest in the field of GaN-based ultraviolet photodetector technology. However, the presence of high dark current deteriorates the photodetector performance by diminishing several figures of merit. In this work, enhanced figures of merit are demonstrated by employing interdigitated p-GaN finger structure on the top of the AlGaN/GaN heterostructure. The commonly present high dark current in p-GaN/AlGaN/GaN planar photodetector is largely reduced (from ≈µA to few pA) by etching the p-GaN, excluding the electrode region. Furthermore, by using a graphene transparent electrode along with the p-GaN interdigitated fingers on AlGaN/GaN heterostructure, ultraviolet photodetectors with superior sensitivity (3.55 × 10⁶) and ultrahigh detectivity (1.91 × 10¹⁴ cm Hz^1/2 W⁻¹) are realized at 360 nm. A comparison of graphene/p-GaN and Ni/Au/p-GaN interdigitated fingers and planar p-GaN (with interdigitated graphene contacts) all on AlGaN/GaN heterostructure allows to understand the dominant roles of electrode transparency and the heterojunction structure. The simple and high electron mobility transistor-compatible fabrication process of UV detectors provides a unique application in the field of UV sensing technology.