The Characterisation of Defects in III-V Semiconducting Compounds by Electron Microscopy.

The two III-V semiconductor compound systems, InP/Ga0.47In0.53As and InxGa1-xAs/GaAs, were examined by transmission electron microscopy (TEM). High resolution electron microscopy (HREM) was used to analyse the interface between InP and GalnAs. Non-standard HREM conditions, such regions of thicker crystal and non-Scherzer defocus were used to optimise the contrast from the two materials. The technique allowed the determination of the planarity of these layers and their transition widths, giving an overall estimate of their quality. The transition width of these samples was found to be no more than three monolayers, with the layers being planar and of good quality. Molecular beam epitaxy (MBE) grown InxGa1-xAs on GaAs substrates was investigated in order to find the critical thickness of InGaAs films. Four compositions were chosen, x=0.1, 0.15, 0.2 and 0.25. It was found that two critical thicknesses exist in this regime, corresponding to surface layers (single layer structure) and buried layers (multi-layer structure). Several critical thickness models from the literature were used to model the experimental determinations of critical thickness. It was found that the models of Matthews and Blakeslee offered poor agreement to both buried and single layers, the best agreement occuring for a refined Matthews and Blakeslee model produced by Miles and McGill. Investigating a series of thicker surface layers, a second critical thickness occured at a thickness predicted by People and Bean. In thick layers it was found that residual strain was still present up until a mismatch of 1.4% (x=0.2).