Large-scale three-dimensional (3-D) device simulations, focused ion microscopy, and broadbeam heavy-ion experiments are used to determine and compare the SEU-sensitive volumes of bulk-Si and SOI CMOS SRAMs. Single-event upset maps and cross-section curves calculated directly from 3-D simulations show excellent agreement with broadbeam cross section curves and microbeam charge collection and upset images for 16 K bulk-Si SRAMs. Charge-collection and single-event upset (SEU) experiments on 64 K and 1 M SOI SRAMs indicate that drain strikes can cause single-event upsets in SOI ICs. 3-D simulations do not predict this result, which appears to be due to anomalous charge collection from the substrate through the buried oxide. This substrate charge-collection mechanism can considerably increase the SEU-sensitive volume of SOI SRAMs, and must be included in single-event models if they are to provide accurate predictions of SOI device response in radiation environments.

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Low-energy ion bombardment of the Ge(001)-(2×1) surface produces surface point defects, which are detected and quantified using in situ reflection high-energy electron diffraction. Surface defect production rates are determined for a range of ion energies and ion masses. At low substrate temperatures (T≊−100 °C), copious production of surface defects is observed, with defect yields as high as 20–30 defects per ion for 500 eV Ar and Xe bombardment. The observed He surface defect yields exceed the surface yield predicted by binary collision simulations, indicating that defects created in the subsurface region migrate to the surface for these conditions. The observed surface defect yield is reduced at elevated substrate temperatures. Based on a simple model this reduction is attributed to surface recombination of point defects created within the same cascade. A constant surface defect yield is reached at temperatures greater than 100 °C which is consistent with the net defect production due to the vacancies left by sputtering. However, even at elevated temperatures, significantly larger populations of mobile point defects than can be accounted for by sputtering may reside transiently on the surface, which can modify the overall surface morphology.

We present reflection high-energy electron diffraction measurements of the evolution of surface morphology during molecular-beam epitaxy of Ge on Ge(001) and subsequent annealing. We find that there is a critical ‘‘kinetic roughening’’ temperature (375 °C) above which a smooth surface remains smooth during growth, but below which it roughens during growth. Surprisingly, smooth starting surfaces never appear to roughen without bound, but reach steady-state roughnesses which depend on temperature and deposition rate. The results can be fit empirically with simple phenomenological equations based on a competition between growth roughening and growth smoothening of a ‘‘pseudo-statistical’’ surface. Furthermore, growth-roughened surfaces tend to smoothen, after growth, at a rate consistent with a third-order power-law ripening mechanism.