Characterization of Epitaxial β-(Al,Ga,In)2O3-Based Films and Applications as UV Photodetectors

Epitaxial films of beta-(AlxGa1-x)(2)O-3, beta-Ga2O3, and beta-(InxGa1-x)(2)O-3 were grown on (001) sapphire substrates via metalorganic chemical vapor deposition (MOCVD). The compositions of the films as determined from energy dispersive x-ray analysis (EDX) and x-ray photoelectron spectroscopy (XPS) results were X-Al = 0.57 +/- 0.05 and 0.76 +/- 0.05 and X-In = 0.12 +/- 0.05 and 0.21 +/- 0.05. The optical bandgap was found to correspondingly vary between 6.0 +/- 0.2 and 3.9 +/- 0.1 eV, as a function of composition via XPS and UV-visible spectroscopy (UV-Vis). X-ray diffraction, scanning electron microscopy, and atomic force microscopy revealed the films to be highly-oriented-epitaxial films with nanocrystalline domains. Schottky- and MSM-based solar-blind UV photodetectors were fabricated on the films and showed responsivities at 20 V varying from > 10(4) A/W for the Ga2O3 devices, > 10(3) A/W for the (AlxGa1-x)(2)O-3 devices and > 10(2) A/W for the (InxGa1-x)(2)O-3 devices. Modest shifts in wavelength selectivity corresponding with the changes in composition/bandgap were also measured. Time response measurements on Schottky and MSM detectors reveal rise and dwell times on the order of a minute, indicating the presence of photoconductive gain. Noise-equivalent powers were in the fW-pW regime with specific detectivities (D*) between 10(10) and 10(12) Jones. Scanning photocurrent maps display large photocurrent generation at the Schottky interface in the case of a beta-Ga2O3 Schottky detector, whereas for an beta-(InxGa1-x)(2)O-3 MSM detector the photocurrent generation occurs in the device channel and at the Schottky interface.