The electron-spin-resonance spectra from surface-strained (but not externally stressed) antimony-doped germanium are investigated in detail. Experimental data are given for the linewidth, line asymmetry, and line-shape reversal feature as well as for the changes in donor concentration, temperature, and surface conditions. The donors of interest occur in a surface layer several microns thick. A theoretical analysis is based on the Kohn-Luttinger formulation for a shallow donor electron, which is forced by surface strain to predominately occupy a [111] conduction-band valley minimum. A substantial distribution in strain among the donor sites is necessary to account for the line-structure features. These features are predicted by a distribution function, which is calculated by using a narrowed Lorentzian line for a homogeneous line shape and a Gaussian strain distribution that determines the inhomogeneous broadening caused by strain-induced g-value variations. The one order of magnitude increase in linewidth with angle is attributed primarily to a g-3 dependence of the linewidth on strain. The asymmetry shape ratio of about 3 is attributed primarily to variations in the valley-population probabilities at different donor sites. The line-shape reversal feature is caused by an angular-dependent variation in the change of the g value with valley-population coefficients. For detailed calculations, distributed strain along the predominately occupied valley axis is assumed. It is found that the average compressive strain along the [111] axis is 10-4 with an accuracy of about 40% and that the Gaussian strain width is 0.6x10-4. This average strain corresponds to a predominant valley occupation of 99%. Our analysis can be used as a semiquantitative tool for determining strain conditions in Ge(Sb). © 1975 The American Physical Society.



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01 Jan 1975

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