EFFECTS OF SUBSTRATE MISORIENTATION ON ORDERING IN GAAS0.5P0.5 GROWN BY ORGANOMETALLIC VAPOR-PHASE EPITAXY

Effects of (001) GaAs substrate misorientation on the formation of the group V sublattice {111} (CuPt) ordered structure are studied for the first time for GaAs0.5P0.5. It is found that the direction of substrate misorientation has a strong effect on the determination of which variants are formed. Two of the four possible ordered variants appear for epilayers grown on exact (001) substrates. The same two variants also appear for the epilayers grown on the (001) substrates misoriented by 6°towards [110]. Only one variant appears on epilayers grown on (001) substrates misoriented by 6°towards the [1̄10] direction. Most significantly, all the ordered-induced diffraction spots in GaAsP are found to occur on the [110] cross section. Thus, the variants found in GaAsP are exactly the same as for GaInP, an alloy with CuPt ordering on the group III sublattice. This result is contradictory to expectations based on the bond-length model proposed previously for GaInP alloys. In addition, for all the 6°misorientated GaAs substrates, independent of the direction of misorientation, large ordered domains with dimensions on the order of micrometers are found in the GaAsP alloys. This has not been reported for other ternary or quaternary alloy systems.