A TEM EVALUATION OF CDTE EPILAYERS GROWN ON PRECISELY ORIENTED (111)B GAAS BY HOT WALL EPITAXY

Structural investigations, using plan-view and cross-sectional transmission electron microscopy (TEM) in addition to etch-pitting techniques, have been carried out on (111BAR)B CdTe epilayers grown on oriented (111BAR)B GaAs substrates by hot wall epitaxy (HWE). The layers are found to exhibit a complex three-dimensional twinning structure which is comprised firstly of a series of lamellar twins extending from the CdTe/GaAs interface to a height of about 6 mum in the epilayer. Above this point, lamellar twinning gives way to a six-fold pattern of single domain sectors with a twinned relationship to each other. The sectors are separated from each other by narrow, mixed domain, boundary regions with radial [110] elongations. The formation of such a twinned structure is explained in terms of epilayer curvature introduced during crystal growth as a consequence on a non-uniform gas flow distribution. In addition, grain structure in the epilayer has been investigated using Electron diffraction analysis and high resolution TEM. Although large angle grain boundaries are found at the interface, a grain regrowth mechanism leads to single crystal CdTe at the epilayer surface, at least in the single domain sectors. Grain boundaries and twin boundaries are found to accumulate in the mixed domain boundary regions. Also, long dislocation tangles are also found to be present in the mixed domain regions.