Transmission Electron Microscopy Characterization of Semiconductors Grown by Organometallic Vapor Phase Epitaxy

Microstructural analysis by transmission electron microscopy has been investigated in this dissertation. Phenomena such as spinodal decomposition and ordering in III/V alloys grown by organometallic vapor phase epitaxy have been the particular topics. No direct evidence of spinodal decomposition was observed in high quality as-grown GaAs_ {0.5}Sb_{0.5} alloys. After annealing, phase separation occurred at the epilayer surface. However, this phenomenon occurred in the as-grown GaAs_{0.5}Sb _{0.5} with high kislocation density due to loss in coherent strain energy stabilization. In GaInAsSb alloys, long wavelength (~ 1000A) spinodal decomposition was also observed. For GaPSb alloy, short wavelength (~45A) spinodal decomposition was observed in high quality GaPSb epilayers. Long range ordered structures were observed for the first time in GaAs_{rm 1 -x}Sb_{rm x} alloys with x ~ 0.5 and 0.75. For GaAs_{0.5}Sb _{0.5} alloys, the kinetic effects leading to the occurrence of ordering were studied, in particular, the effects of growth temperature, growth rate, and substrate orientation. The ordered L1 _0 and E1_1 structures were observed to coexist at the highest growth temperatures from 580 to 650^circC. The L1_3 ordered structure was observed in GaAs_{0.25}Sb _{0.75} alloys. For a Ga_{0.63}In _{0.37}As_ {0.98}Sb_{0.02} layer, a 20-30 A periodicity was superposed on the ordered L1_0 and E1 _1 structures. The first L1_1 ordering was also observed in InAs_{rm 1-x}Sb_{rm x} alloys over a wide compositional range from x = 0.22 to 0.88. The order-induced spots for the L1 _1 ordered structure show the highest intensity for samples with x ~ 0.5 and the lowest intensity toward each binary end compound. Only two of the four variants are formed during growth. The first observation of L1_1 ordering in GaAs_{rm 1-x} P_{rm x} alloys (at compositions of x = 0.3 and 0.4) is also reported. Only two of the four variants were observed. The degree of ordering along the 1over2(111) direction is higher than for the other variant, ordered along the 1over2 (111) direction. In addition, the degree of ordering decreases when x is reduced from 0.4 to 0.3. The two variants of the CuPt type ordered structure were also observed in InP_{0.5} Sb_{0.5} alloys. However, the elongation of each order-induced spot indicates a plate -like domain shape.