Effect of Uniaxial Stress on the Excitation Spectra of Donors in Silicon

The excitation spectra of neutral shallow group V donors in silicon, viz., phosphorus, antimony, and arsenic, have been measured with crystals subjected to compression, F, along the [100], [110], or [111] direction. Each excitation line is observed to undergo a splitting into two components for F ∥ [100] or F∥ [110], the spacing between the components being the same for all the lines. The spectra were measured with polarized light, the direction of polarization being either parallel or perpendicular to the compressive force. The split components of the excitation lines exhibit pronounced polarization. The splittings can be ascribed to the splitting of the excited $p$ states arising from the energy shifts of the conduction-band minima in uniaxially stressed silicon. The polarization features have been interpreted on the basis of the new site symmetry of the substitutional donor atom in the stressed crystal. The absence of splittings for F ∥ [111] follows from the preservation of the energy equivalence of the six valleys even under stress.