MBE growth of GaN and AlGaN layers on Si(111) substrates:: doping effects

High-quality GaN layers with 8 arcmin (X-ray diffraction full-width at half-maximum, XRD FWHM) and rms surface roughness of 57 Angstrom are grown on Si(111) substrates when using optimized AIN buffer layers. Si-doping produces n-type films reaching carrier concentrations up to 1.7 x 10(19) cm(-3) with mobilities of 100 cm(2)/V s. A reduction of the lattice parameter c together with a red shift in the photoluminescence (PL) emission is observed with increasing Si doping. The dislocation density observed by plan-view transmission electron microscopy (PVTEM) also decreases by close to one order of magnitude (from 5.3 x 10(9) to 8 x 10(8) cm(-2)) when increasing the Si doping (from 1.1 x 10(17) to 6.0 x 10(18) cm(-3)). AlGaN layers were grown with Al content ranging from 10% to 76% with XRD FWHM of 22 arcmin and intense low-temperature photoluminescence. N-type doping is achieved in AlGaN (40%) with Si, reaching electron concentrations of 8 x 10(19) cm(-3). (C) 1999 Elsevier Science B.V. All rights reserved.