The orientation dependence of phase separation has been examined in detail in InGaAsP layers grown by liquid phase epitaxy on (001), (110), (111)ln and (123) InP substrates. It is shown that phase separation is two-dimensional in nature and does not occur along the growth direction for the cases examined. Further, phase separation takes place along the soft directions lying in the growth plane. These results very strongly suggest that phase separation evolves at the surface while the layer is growing. CuPt-type ordering characteristics of InGaAsP layers are presented. In addition, the Influence of growth temperature and growth rate on domain sizes have been investigated in GaInP2 layers. A model has been proposed to rationalize the formation of domains and involves steps present on the surface. Results suggest that ordering like phase separation occurs at the surface while the layers is being deposited. It is inferred that the two microstructural features evolve concomitantly at the surface during layer growth.

Microstructures of lattice-matched In1-xGaxAsyP1-y epitaxial layers, grown on (001), (110), (111)A, and (123) InP substrates by use of liquid-phase epitaxy, have been examined in detail by transmission electron microscopy. Results indicate that the fine-scale speckle microstructure is caused by two-dimensional phase separation occurring at the surface while the layer is growing; decomposition along the growth direction is not observed in either of the four cases examined. The decomposition is found to take place along those directions in the growth plane along which the elastic work associated with the transformation is a minimum. The temperature dependence of the wavelength of the fine-scale structure in (001) In1-xGaxAs epitaxial layers grown by use of molecular-beam epitaxy indicates that the wavelength evolution is controlled by the surface diffusion of As atoms.

The influence of annealing on phase separated microstructures in lattice-matched InGaAsP epitaxial layers, grown on (001) InP substrates by liquid phase epitaxy, has been investigated. It is shown that the fine and coarse contrast modulations commonly observed in these layers are coupled. This observation is consistent with the suggestion that the fine scale structure causes the coarse modulations. Further, the carrier mobility and the carrier concentration increase on annealing.

Homoepitaxial layers of undoped InP were grown by liquid phase epitaxy in a vertical system using different equilibration temperatures and supercooling. The quality of the as-grown epilayers was assessed by the Hall effect and photoluminescence (PL) measurements. It is found that the layers exhibit a residual n-type conductivity and that the values of electron concentration and mobility vary throughout the thickness of a given epilayer. Moreover, the electron concentration is high with correspondingly low values of electron mobility in the first-to-grow regions of the epilayers. The PL measurements agree with the Hall data and show that the material quality is relatively poor when the layers are grown at a higher rate. On the basis of PL data, a window of processing parameters is identified where optimum luminescence properties are observed. The measured thicknesses of the epilayers are consistent with diffusion controlled mechanisms of epitaxial growth.

LPE InGaAsP layers and MBE InGaAs layers grown on (001) and (111) InP substrates have been examined by cross-sectional and plan-view TEM in order to assess the effect of substrate orientation on modulated microstructures in these layers. The fine-scale contrast modulations have been observed to be two dimensional regardless of substrate orientation. This observation has been shown to be consistent with spinodal decomposition at the surface of the film.

Small angle neutron scattering on CuCo alloys containing 0.5 and 0.8 at.% Co gives evidence for precursor stages of decomposition prior to the α-phase precipitation, characterized as compositional fluctuations, small in amplitude but large in size as compared to the subsequently forming α-precipitates. The fluctuations obviously give rise to a nucleation rate significantly higher than predicted by classical nucleation theory.