CORRELATION BETWEEN SURFACE-STRUCTURE AND ORDERING IN GAINP

Ga and In atoms in Ga0.52In0.48P layers spontaneously segregate to for m alternating In- and Ga-rich {111} monolayers during organometallic v apor phase epitaxial (OMVPE) growth on (001) oriented GaAs substrates, thus forming the CuPt ordered structure. This ordering phenomenon is believed to be driven by surface processes, although little direct exp erimental information is available. This work presents evidence, based on surface photoabsorption data, that [<(1)over bar 10>] oriented P d imers are present on the surface during OMVPE growth using trimethylga llium and ethyldimethylindium combined with tertiarybutylphosphine, su ggesting a (2x4)-like surface reconstruction. Furthermore, when the gr owth temperature is increased above 620 degrees C, with other paramete rs constant, both the concentration of these P dimers and the degree o f order are observed to decrease. A similar correlation of decreased P -dimer concentration with decreased degree of order is observed for de creases in V/III, ratio. Thus, the changes in order parameter for vari ations in temperature and TBP flow rate are found to be closely correl ated with the changes in the order parameter. A third parameter studie d was the misorientation of the substrate from (001) toward either the {111}(A) or {111}(B) planes. The concentration of P dimers decreased as the misorientation increased in either direction. The degree of ord er was also observed to generally decrease, supporting the connection between surface reconstruction and ordering. However, the difference i n order parameter observed for the two misorientation directions sugge sts the importance of a second parameter, the step structure, itself. For exactly (001) oriented substrates the surface was observed, using high resolution atomic force microscopy, to consist of islands, elonga ted in the [110] direction, with heights of 30-60 Angstrom. Monolayer steps are observed for some growth conditions, but for most conditions the boundaries are formed exclusively of bilayer (5.7 Angstrom) steps . Predominantly monolayer steps are formed for low V/III ratios and bi layer steps for high V/III ratios. (C) 1996 American Vacuum Society.