ATOMIC ORDERING IN INAS0.5P0.5 GROWN BY ORGANOMETALLIC VAPOR-PHASE EPITAXY

InAsP epilayers grown by organometallic vapor phase epitaxy have been investigated using transmission electron microscopy. Electron diffraction studies using <110> cross sections indicate the formation of CuPt-like ordering on the group V sublattice. Only two of the four possible ordered variants are observed for epilayers grown on the exactly (001) oriented InP substrates. All the order-induced diffraction spots for InAsP are found to occur on the [110] cross section. Thus, the variants found in InAsP are 1/2 (1BAR11) and 1/2(11BAR1), exactly the same as those found in GaInP, an alloy with CuPt ordering on the group III sublattice. This result is in agreement with recent studies on GaAsP and is contradictory to expectations based on the bond-length model proposed previously for GaInP alloys. The direction of substrate misorientation has a strong effect on the formation of ordered structures for normally (001) oriented InP substrates.