<title>Al<formula><inf><roman>x</roman></inf></formula>Ga<formula><inf><roman>1-x</roman></inf></formula>N materials and device technology for solar blind ultraviolet photodetector applications</title>

TLDR

Solar‑blind UV photodetectors are sought for missile warning, flame monitoring, UV and chemical/biological detection, and AlGaN is the most promising material system, though its quality control and device technology remain immature. The authors grew high‑quality AlxGa1−xN thin films on sapphire by MOCVD, doped them n‑ and p‑type across a wide Al range, and developed low‑resistance ohmic contacts up to 40 % Al to improve device performance. They fabricated p‑i‑n photodiodes with cut‑off wavelengths tunable from 227 to 365 nm, internal quantum efficiencies up to 86 %, and UV‑to‑visible rejection ratios of six orders, demonstrating both front‑ and back‑illuminated devices and lateral‑epitaxial‑overgrowth GaN photodetectors.

Abstract

There has been a growing interest for the development of solar blind ultraviolet (UV) photodetectors for use in a variety of applications, including early missile threat warning, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The Al<SUB>x</SUB>Ga<SUB>1-x</SUB>N material system has emerged as the most promising approach for such devices. However, the control of the material quality and the device technology are still rather immature. We report here the metalorganic chemical vapor deposition, the n-type and the p-type doping of high quality Al<SUB>x</SUB>Ga<SUP>1-x</SUP>N thin films on sapphire substrates over a wide range of Al concentration. The quality of this Al<SUB>x</SUB>Ga<SUB>1-x</SUB>N material was verified through the demonstration of high performance visible and solar blind ultraviolet p-i-n photodiodes with a cut-off wavelength continuously tunable from 227 to 365 nm, internal quantum efficiencies up to 86% when operated in photovoltaic mode, and a ultraviolet-to-visible rejection ratio as high as six orders of magnitude. Both front and back side illuminated p-i-n photodiodes were realized. Photodetector devices were also demonstrated on GaN material obtained using lateral epitaxial overgrowth. The technology for such Al<SUB>x</SUB>Ga<SUB>1-x</SUB>N based devices was improved in an effort to enhance their performance, including the development of ohmic metal contacts to both n-type and p-type Al<SUB>x</SUB>Ga<SUB>1-x</SUB>N films with an Al concentration up to 40%.