Structural studies of natural superlattices in group III-V alloy epitaxial layers

Structural studies have been performed using transmission electron microscopy and diffraction on III-V ternary and quaternary alloy epitaxial layers. The results revealed that 'natural superlattice' structures had spontaneously formed in some of the layers by phase separation and/or atomic ordering which occurred at the surface during growth. The structure of these natural superlattices and the growth conditions for their occurrence are described and their effect on the electrical and optical properties of the layers, e.g. bandgap narrowing, and possible mechanisms of formation are briefly discussed.