Metalorganic vapor-phase epitaxy-grown AlGaN materials for visible-blind ultraviolet photodetector applications

Low-pressure metalorganic vapor-phase epitaxy growth conditions of AlxGa1-xN epilayers on c-oriented sapphire have been optimized for aluminum mole fractions x lying in the 0-0.35 range both on GaN and AlN nucleation layers, with a view to application in visible blind UV photodetectors. Good structural, electrical, and optical properties were obtained for undoped and n-type doped AlGaN alloys on (0001)-oriented sapphire substrates. A typical full width at half maximum of 670-800 arc s is measured for the (0002) x-ray double-diffraction peak in the omega mode of 1-mu m-thick AlGaN epilayers grown on a GaN nucleation layer. Room-temperature electron mobilities up to 90 cm(2)/V s are measured on n-type (10(18) cm(-3)) AlGaN epilayers. The low-temperature photoluminescence (T=9 K) performed on nonintentionally doped AlGaN epilayers with low-Al content (10% and 14%) exhibits reproducibly a sharp exciton-related peak, associated with two phonon replica and does not exhibit any low-photon energy transitions. Optical transmission as well as absorption coefficient measurements using photothermal deflection spectroscopy have been used to study the variation of the T=300 K energy gap of AlGaN with the aluminum concentration. Visible-blind AlGaN(Si)-based photoconductors and Schottky barrier photodiodes with good operating characteristics have been fabricated with these materials. (C) 1999 American Institute of Physics. [S0021- 8979(99)08221-3].