Optical reflectivity studies of GaN and AlN chemical beam epitaxy on GaAs(100)

The deposition of gallium nitride and aluminium nitride thin films on GaAs(100) substrates by chemical beam epitaxy is reported. In-situ dynamic optical reflectivity has been used to compare growth rates of the nitride layers as a function of substrate temperature with their arsenide analogues. The relative growth efficiency of gallium nitride/gallium arsenide from triethyl gallium was found to be in the range 75–85%. The growth temperature for gallium nitride extends to higher temperatures, compared with gallium arsenide, probably due to lower evaporation rates of Ga bound to the nitride surface. At the same beam equivalent pressure, the growth rate of aluminium nitride from ethyldimethyl aluminium alane is approximately one-third of that for gallium nitride from triethyl gallium. Atomic force microscopy reveals that the gallium nitride surface formed at 500°C is facetted, whereas an aluminium nitride surface deposited at 400°C exhibits a rounded columnar type growth habit. Reflection anisotropy spectra indicate that atomic nitrogen readily reacts with the GaAs(100)-c(4×4) As stabilized surface at temperatures as low as 400°C but without the gross facetting that has been observed at higher temperatures.