REFLECTANCE ANISOTROPY FROM (001) GAAS-SURFACES DURING PSEUDO-ALE GROWTH OF GAAS

We demonstrate that the technique of reflectance anisotropy (RA) has n ow evolved to the level of sophistication required to be of use in dir ect MOVPE process control. Comparison with data obtained under high va cuum GaAs MBE growth and vacuum chemical epitaxy growth conditions per mits the interpretation of RA changes that occur under higher pressure growth conditions. Inflections in RA responses can indicate changes i n surface reconstruction that occur again both under high vacuum condi tions and at higher pressures. Under pseudo-ALE growth of GaAs on (001 ) GaAs from triethylgallium (TEGa) and arsine in a conventional hot-wa ll MOVPE reactor maintained at a constant pressure of 200 mbar, the on set of Ga incorporation via TEGa decomposition has been monitored as a function of substrate temperature. For this reaction, where the rate- determining step may occur either homogeneously in the gas phase or he terogeneously on the substrate surface, changes in RA intensity have b een observed at temperatures as low as 350-degrees-C. Under these cond itions, while the surface changes resulting from TEGa decomposition oc cur quite slowly, the subsequent surface recovery upon exposure to ars ine gas in the second half of the growth cycle occurs very rapidly, th e data suggesting that the surface initially relaxes beyond the initia l As-stabilised surface towards a very As-rich surface in response to an oversaturation of the surface with Ga atoms during the first half o f the growth cycle. This surface then slowly loses As to return to the stable initial condition. In order to observe the arsine recovery kin etics in more detail, the flow rates were reduced. Under these conditi ons, while rapid RA variations were again observed, inflections in the RA responses became increasingly prominent, which are discussed in te rms of possible surface reconstructions that may occur during recovery back to the initial surface condition.