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 reduction in bandgap energy. The degree of order is known to be a strong function of the input partial pressure of the P precursor during growth due to the effect of this parameter on the surface reconstruction. This raises the possibility of producing heterostructures by simply changing the flow rate of the P precursor during growth. The change in bandgap energy at order/disorder (O/D) heterostructures formed by decreasing the P partial pressure during the OMVPE growth cycle is graded over several thousands of Å when PH₃ is used as the P precursor. Examination of the transmission electron microscope image and the photoluminescence (PL) spectrum reveals that the ordered structure in the lower layer persists far into the upper layer. Similarly, disorder/order (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 cycle for as long as one hour. Similar heterostructures produced using tertiarybutylphosphine (TBP) as the P precursor are distinctly different. Both D/O and O/D heterostructures can be produced by abruptly increasing the TBP flow rate during the growth cycle. PL studies show two distinct peaks closely corresponding to those observed for single layers grown using these conditions. Surface photoabsorption spectroscopy was 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 behavior between PH₃ and TBP is that atomic force microscopy scans show the layers grown using TBP are covered by monolayer and bilayer (6 Å in height) steps. Growth under similar conditions using PH₃ produces bunched steps, much larger than 6 Å in height.