Metalorganic molecular beam epitaxy of GaN and Al(Ga)N on GaAs(001) studied using laser reflectometry and reflectance anisotropy spectroscopy

We report the growth of GaN and AlGaN films on GaAs (0 0 1) substrates in t he temperature range 400-800 degrees C by metalorganic molecular beam epita xy. An r.f. plasma nitrogen source was used in conjunction with triethylgal lium and ethyl-dimethylamine-alane group III sources. Growth was initiated using either a low temperature AlN buffer layer or a graded arsenide-nitrid e buffer layer. The growth was monitored in real time using in-situ laser r eflectometry. The temperature dependence of growth rates for the nitride la yers are compared with their arsenide analogs. The relative growth rate of gallium nitride/gallium arsenide from triethylgallium was found to be in th e range 54-60%, the Ga incorporation rates are closely comparable when the higher density of GaN is taken into account. The range of growth temperatur es for gallium nitride extends to higher temperatures compared with gallium arsenide probably due to lower evaporation rates of Ga bound to the nitrid e surface. Reflection anisotropy spectra indicate that atomic nitrogen read ily reacts with the GaAs (0 0 1)-c (4 x 4) As-stabilized surface at tempera tures as low as 400 degrees C but without the gross faceting that has been observed at higher temperatures.