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 the temperature range 400–800 °C by metalorganic molecular beam epitaxy. An r.f. plasma nitrogen source was used in conjunction with triethylgallium and ethyl-dimethylamine-alane group III sources. Growth was initiated using either a low temperature AlN buffer layer or a graded arsenide-nitride buffer layer. The growth was monitored in real time using in-situ laser reflectometry. The temperature dependence of growth rates for the nitride layers are compared with their arsenide analogs. The relative growth rate of gallium nitride/gallium arsenide from triethylgallium was found to be in the range 54–60%, the Ga incorporation rates are closely comparable when the higher density of GaN is taken into account. The range of growth temperatures for gallium nitride extends to higher temperatures compared with gallium arsenide probably due to lower evaporation rates of Ga bound to the nitride surface. Reflection anisotropy spectra indicate that atomic nitrogen readily reacts with the GaAs (0 0 1)-c (4 × 4) As-stabilized surface at temperatures as low as 400 °C but without the gross faceting that has been observed at higher temperatures.