SURFACE PHOTOABSORPTION TRANSIENTS AND ORDERING IN GAINP

Heterostructures and quantum wells can be produced in GaInP without ch anging the solid composition by simply varying the order parameter. Si nce CuPt ordering reduces the band-gap energy, changes in the order pa rameter induced by changes in growth conditions result in heterostruct ures with band-gap energy discontinuities as large as 160 meV. The mos t convenient growth parameter to change is the flow rate of the P prec ursor. However, previous work has shown that under some conditions the change in order parameter is sluggish, giving rise to graded heterost ructures. The cause of the slow change in order parameter is the topic of this article. CuPt ordering has been shown to be driven by the for mation of [(1) over bar 10] P dimers, characteristic of the (2X4) surf ace reconstruction. Thus, this study of the transient in the degree of order induced by changing the flow rate of the P precursor has relied on the use of surface photoabsorption (SPA) to monitor the surface re construction during the period after the partial pressure of the P pre cursor was reduced. The SPA transient has then been correlated with th e abruptness of the heterostructure interface, determined from the tra nsmission electron microscopy images and the photoluminescence spectra , for organometallic vapor phase epitaxial (OMVPE) growth at temperatu res of 620 and 670 degrees C using the P precursors phosphine (PH3) an d tertiarybutylphosphine (TBP). For TBP at both 620 and 670 degrees C, the SPA reflectance transient is extremely short, with a time constan t of less than 10 s, corresponding to the time response of the OMVPE g rowth system. Abrupt interfaces are produced using these conditions. F or PH3, the SPA reflectance transient is abrupt at 670 degrees C; howe ver, at 620 degrees C the SPA response is extremely sluggish, with a t ime constant of approximately 6.5 min. The effect is tentatively attri buted to a surfactant effect due to H on the surface. Corresponding he terostructures were abrupt at 670 degrees C and graded at 620 degrees C. (C) 1998 American Institute of Physics.