GROWTH OPTIMIZATION AND DOPING WITH SI AND BE OF HIGH-QUALITY GAN ON SI(111) BY MOLECULAR-BEAM EPITAXY

GaN layers have been grown by plasma-assisted molecular beam epitaxy o n AIN-buffered Si(111) substrates. An initial Al coverage of the Si su bstrate of approximately 3 nm lead to the best AIN layers in terms of x-ray diffraction data, with values of full-width at half-maximum down to 10 arcmin. A (2 x 2) surface reconstruction of the AIN layer can b e observed when growing under stoichiometry conditions and for substra te temperatures up to 850 degrees C. Atomic force microscopy reveals t hat an optimal roughness of 4.6 nm is obtained for AIN layers grown at 850 degrees C. Optimization in the subsequent growth of the GaN deter mined that a reduced growth rate at the beginning of the growth favors the coalescence of the grains on the surface and improves the optical quality of the film. Following this procedure, an optimum x-ray full- width at half-maximum value of 8.5 arcmin for the GaN layer was obtain ed. Si-doped GaN layers were grown with doping concentrations up to 1. 7 x 10(19) cm(-3) and mobilities approximately 100 cm(2)/V s. Secondar y ion mass spectroscopy measurements of Be-doped GaN films indicate th at Be is incorporated in the film covering more than two orders of mag nitude by increasing the Be-cell temperature. Optical activation energ y of Be accepters between 90 and 100 meV was derived from photolumines cence experiments.