USE OF V III RATIO TO PRODUCE HETEROSTRUCTURES IN ORDERED GAINP/

Compositional ordering in Ga-0.52 In-0.48 P results in a significant r eduction in bandgap energy. The degree of order is known to be a stron g function of the input partial pressure of the P precursor during gro wth due to the effect of this parameter on the surface reconstruction. This raises the possibility of producing heterostructures by simply c hanging the flow rate of the P precursor during growth. The change in bandgap energy at order/disorder (O/D) heterostructures formed by decr easing the P partial pressure during the OMVPE growth cycle is graded over several thousands of Angstrom when PH3 is used as the P precursor . Examination of the transmission electron microscope image and the ph otoluminescence (PL) spectrum reveals that the ordered structure in th e lower layer persists far into the upper layer. Similarly, disorder/o rder (D/O) structures produced in this way yield PL spectra indicative of graded composition at the heterostructure when the P precursor is PH3. The abruptness is not affected by interruptions in the growth cyc le for as long as one hour. Similar heterostructures produced using te rtiarybutylphosphine (TBP) as the P precursor are distinctly different . Both D/O and O/D heterostructures can be produced by abruptly increa sing the TBP flow rate during the growth cycle. PL studies show two di stinct peaks closely corresponding to those observed for single layers grown using these conditions. Surface photoabsorption spectroscopy wa s used to monitor the transition in surface reconstruction. The change was found to be limited by the dynamics of the mass flow controller. The only difference detected which might explain the difference in beh avior between PH3 and TBP is that atomic force microscopy scans show t he layers grown using TBP are covered by monolayer and bilayer (6 Angs trom in height) steps. Growth under similar conditions using PH3 produ ces bunched steps, much larger than 6 Angstrom in height.