Growth of AlGaN on Si(111) by gas source molecular beam epitaxy

Gas source molecular beam epitaxy with ammonia was used to grow AlxGa1-xN o n Si(111). Three types of buffer layers, containing AlN, AlGaN/AlN, and AlG aN/GaN short period superlattices, were used and their effectiveness evalua ted by x-ray diffraction. We determined that a combination of AlN buffer la yer, prepared under the two-dimensional growth mode, with a short period su perlattice of AlGaN/GaN results in the highest quality AlGaN. Under optimiz ed growth conditions, x-ray diffraction coherence length almost equal to th e layer thickness was obtained for low Al content layers. The normalized co herence length was reduced to similar to 0.4 for x=0.66 and it increased ag ain to similar to 0.75 in AlN. From room temperature band edge cathodolumin escence of AlGaN grown on Si(111) we determined the alloy bowing coefficien t of b=1.5 eV, in good agreement with previous results obtained by absorpti on measurements. (C) 2000 American Institute of Physics. [S0003-6951(00)036 21-4].