Correlation between surface structure and ordering in GaInP

Abstract

Ga and In atoms in Ga0.52In0.48P layers spontaneously segregate to form alternating In- and Ga-rich {111} monolayers during organometallic vapor 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 experimental information is available. This work presents evidence, based on surface photoabsorption data, that [1̄10] oriented P dimers are present on the surface during OMVPE growth using trimethylgallium and ethyldimethylindium combined with tertiarybutylphosphine, suggesting a (2×4)-like surface reconstruction. Furthermore, when the growth temperature is increased above 620 °C, with other parameters constant, both the concentration of these P dimers and the degree of order are observed to decrease. A similar correlation of decreased P-dimer concentration with decreased degree of order is observed for decreases in V/III ratio. Thus, the changes in order parameter for variations in temperature and TBP flow rate are found to be closely correlated with the changes in the order parameter. A third parameter studied 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 order was also observed to generally decrease, supporting the connection between surface reconstruction and ordering. However, the difference in order parameter observed for the two misorientation directions suggests 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, elongated in the [110] direction, with heights of 30–60 Å. Monolayer steps are observed for some growth conditions, but for most conditions the boundaries are formed exclusively of bilayer (5.7 Å) steps. Predominantly monolayer steps are formed for low V/III ratios and bilayer steps for high V/III ratios.