Effect of P precursor on surface structure and ordering in GaInP

Surface photo absorption (SPA) is one of the only techniques for characterization of the surface structure during organometallic vapor-phase epitaxial (OMVPE) growth. Since the ordering process leading to the formation of the CuPt structure in III/V alloys occurs completely at the surface during growth, SPA gives valuable information about the ordering process. In this study SPA was used to characterize the surface during OMVPE growth of GaInP at 670 degrees C using several partial pressures of the phosphorus precursor. Results for the two precursors tertiarybutylphosphine (TBP) and phosphine were compared in detail. The SPA signal difference at 400 nm, attributed to the [(1) over bar 1 0]P dimers characteristic of the (2 x 4) reconstructed surface, was found to increase with increasing partial pressure with equal magnitudes, to within experimental error, for PH, and TBP. The degree of order in the resulting epitaxial layers was also found to increase with increasing partial pressure of the P precursor and to be virtually identical for the two precursors. A surprising difference between the two P precursors relates to the transient in the 400 nm SPA reflectivity when the flow of the P precursor is terminated. For TBP at both 620 and 670 degrees C, the SPA reflectivity transient is rapid. For PH,, the SPA reflectivity transient is delayed for approximately 1 min at 670 degrees C. At 620 degrees C the SPA response is extremely sluggish, with a time constant of approximately 6.5 min. The step structure, measured using atomic force microscopy, is also found to be different for the two P precursors. For PH3 the steps are mainly monolayers and for TBP they are mainly bilayers. Both differences are tentatively attributed to the difference in H coverage of the surface for the two precursors. (C) 1998 Elsevier Science B.V. All rights reserved.