Low pressure MOVPE grown AlGaN for UV photodetector applications

The low pressure Metalorganic Vapor Phase Epitaxy (LP-MOVPE) growth conditi ons of AlGaN epilayers on c-oriented sapphire have been optimized with a vi ew to application to UV photodetectors both on GaN and AIN nucleation layer s, for aluminium mole fractions lying typically in the range 0-25%. Good st ructural, electrical and optical properties were obtained for AlGaN alloys on (0001) oriented sapphire substrates, for both undoped and n-type doped e pilayers. A typical full width at half maximum (FWHM) of 670-700 arc-s is m easured for the (0002) X-ray double diffraction peak in the omega-configura tion of 1 mu m-thick AlGaN epilayers grown on a GaN nucleation layer, and a typical electron mobility of 50-90 cm(2) V-1 s(-1) is measured at T = 300 K on 10(18) cm(-3) n-type doped AlGaN epilayers. The low temperature photol uminescence (T = 9 K) performed on non intentionally doped AlGaN epilayers with low Al contents (5 and 10%) exhibits reproducibly a sharp exciton-rela ted peak, associated with two phonon replica and a total absence of low pho ton energy transitions. Optical transmission as well as absorption coeffici ent measurements using the photothermal deflection spectroscopy (PDS) clear ly show that the variation of the energy gap of AlGaN with the aluminium co ncentration is linear. Solar-blind AlGaN-based photoconductors and Schottky barrier photodiodes with good operating characteristics have been fabricat ed with these materials. (C) 1999 Elsevier Science S.A. All rights reserved .