SURFACE PHOTOABSORPTION STUDY OF THE EFFECT OF V III RATIO ON ORDERING IN GAINP/

Cu-Pt ordering is widely observed in Ga0.5In0.5P layers grown by organ ometallic vapor phase epitaxy. The degree of order is a strong functio n of the input partial pressure of the phosphorus precursor, i.e., the V/III ratio, during growth. By observing the surface structure using in situ surface photoabsorption (SPA) measurements, the concentration of [<(1)over bar 10>]-oriented P dimers, characteristic of the (2x4) r econstructed surface, has been measured as a function of the growth co 0.nditions. For growth at 670 degrees C, the P-dimer concentration is found to increase systematically as the input tertiarybutylphosphine p ressure is increased from 10 to 200 Pa. This corresponds directly to a monotonic increase in the degree of order, measured using transmissio n electron microscopy and low-temperature photoluminescence. These dat a strongly suggest that the (2x4) surface reconstruction is necessary for formation of the Cu-Pt structure. The step structure at the surfac e was also observed for these layers using atomic force microscopy. Fo r high V/III ratios the structure of the layers grown on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bil ayer (5.7 Angstrom) steps. As the V/III ratio is reduced, the step hei ght transforms to 2.8 Angstrom (one monolayer). (C) 1996 American Inst itute of Physics.