Ultraviolet Detectors and Focal Plane Array Imagers Based on AlxGa1-xN P-I-N Photodiodes

Abstract

This research has been conducted in order to address the absence of effective solid-state ultraviolet (UV) detectors and imagers. Despite the wide range of advances in visible and infrared imagery, until recently there have been no semiconductor devices under development for imaging strictly in the ultraviolet region of the spectrum. Much of the difficulty in creating such devices has been due to the lack of appropriate materials; however, the development of the group III-nitrides (III-N), including materials such as GaN and AlGaN, has provided a solution to this dilemma. The AlxGa1-xN based devices synthesized during this research were grown via organo-metallic vapor phase epitaxy and processed using standard photolithography, e-beam evaporation, and reactive ion etching processes. Focal plane arrays were subsequently bump bonded to silicon read-out integrated circuits (ROICs), which were then wire bonded to 84-pin leadless chip carriers. A specialized video camera and focal plane array evaluation software were used to test the imagers. The devices exhibit very low noise and very high sensitivity to ultraviolet radiation. Excellent quality UV images have been obtained for both 128x128 and 320x256 large format hybridized focal plane arrays. These new devices may find widespread usage in a number of applications that require sensitive UV detectors and UV imagers but where the cost, size, and power requirements of a photomultiplier tube cannot be justified.