Ballistic-electron-emission microscopy of strain nonuniformities in Si1-xGex/Si structures.

Ballistic-electron-emission microscopy (BEEM) is used to probe local conduction-band structure in strained Sil .xGq layers of pseudomorphic Sil-xGe#Si heterostmctires. The strain variation produced by a roughened Si l.xGex surface is seen as a variation of splitting between thresholds in BEEM spectroscopy. This splitting is directly related to the strain-induced conduction-band splitting in the Sil-xG~ layer, enabling BEEM to directly measure local strain variations. Elasticity calculations for a roughened Sil-xGex surface predict variations in strain that are consistent with BEEM observations. For the case of a smooth Sil .xGex surface, a uniform conduction-band splitting is observed which is in good agreement with calculations.