We report on the microstructural characterization of monolithically integrated II-VI and III-V heterostructures that are being developed for possible solar cell applications. Observations by transmission electron microscopy have shown that the growth of lattice-matched ZnTe layers on GaSb(100) substrates resulted in very high quality interfaces and very few structural defects. We then investigated short-period superlattices (SSLs) of CdSe and CdTe digital alloys grown using ZnTe buffer layers on GaSb substrates. The effect of rapid thermal annealing was also studied. High-resolution electron micrographs showed that the CdSe-CdTe SSL had very high quality for approximately 25-50 periods closest to the substrate but that considerable stacking faults and microtwins were visible in layers near the top surface of the sample. For comparison purposes, CdSe layers grown on InAs(100) substrates, again using ZnTe as a buffer layer, were also characterized. The quality of the CdSe layer was not as good as that observed in the SSL sample, possibly because of the larger lattice mismatch between the materials.

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