Observation of weak ordering effects and surface morphology study of InGaP grown by solid source molecular beam epitaxy
We report the characterization of InGaP grown lattice-matched to GaAs using a valved phosphorus cracker cell in solid source molecular beam epitaxy (SSMBE) over a wide range of substrate temperature (Ts from 420 to 540C). The optical bandgap and lattice-mismatch were determined using low temperature photoluminescence (PL) and X-ray diffraction (XRD). Raman scattering measurements showed signals at 330, 360 and 380cm?1 which correspond to the InP-like transverse-optic (TO), InP-like longitudinal-optic (InP-LO) and GaP-like LO modes, respectively. The sample grown at Ts=540C showed poor surface morphology caused by indium desorption as verified by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examination. The optical bandgap decreased marginally (?23meV) while the ordering parameter increased slightly in samples grown at an increasing substrate temperature. The relatively small variation in the Raman intensity of the InP-like and GaP-like LO mode and the marginal decrease in the valley-to-peak intensity ratio of the InP-like LO mode indicate the presence of relatively weak ordering effects in the material. Further evidence of weak CuPt-type ordering comes from the observation of a signal at 354cm?1 in the Raman spectrum.
solid source molecular beam epitaxy (ssmbe) raman scattering measurement ingap samples