ELECTRONIC CONTRIBUTION TO SECONDARY-ELECTRON COMPOSITIONAL CONTRAST IN THE SCANNING ELECTRON-MICROSCOPE

Scanning electron microscopy of cleavage surfaces through a variable t hickness Si-Ge0.25Si0.75 heterostructure is shown to reveal the high s ensitivity of the secondary electron signal to small changes in band s tructure. Ge0.25Si0.75 layers that are coherently strained appear brig hter in secondary electron micrographs than equal thickness layers of the unstrained Ge0.25Si0.75 alloy. This effect has been studied quanti tatively and is explained in terms of the 0.1. eV strain-induced raisi ng of the Ge0.25Si0.75 valence band edge resulting in an increased sec ondary electron escape probability.