EFFECT OF P-PRECURSOR ON SURFACE-STRUCTURE AND ORDERING IN GAINP

Surface photo absorption (SPA) is one of the only techniques for chara cterization of the surface structure during organometallic vapor-phase epitaxial (OMVPE) growth. Since the ordering process leading to the f ormation of the CuPt structure in III/V alloys occurs completely at th e surface during growth, SPA gives valuable information about the orde ring process. In this study SPA was used to characterize the surface d uring OMVPE growth of GaInP at 670 degrees C using several partial pre ssures of the phosphorus precursor. Results for the two precursors ter tiarybutylphosphine (TBP) and phosphine were compared in detail. The S PA 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 th e resulting epitaxial layers was also found to increase with increasin g partial pressure of the P precursor and to be virtually identical fo r the two precursors. A surprising difference between the two P precur sors 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 deg rees C, the SPA reflectivity transient is rapid. For PH,, the SPA refl ectivity 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 a re mainly bilayers. Both differences are tentatively attributed to the difference in H coverage of the surface for the two precursors. (C) 1 998 Elsevier Science B.V. All rights reserved.