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Effect of strains and electronic fields on the acceptor states in boron-doped silicon White, James Judson

Abstract

In boron doped silicon, optical excitation of bound holes from the ground state to the various excited states of the neutral acceptor impurity leads to an absorption line spectrum. By applying an external strain, the degeneracies of the acceptor ground state and the four lowest "observable" excited states were determined and were found to only partially agree with theory (Schechter 1962). By applying a uniform electric field to compensated samples, the "Stark effect" for the acceptor states was observed. The Stark shift of the excited states is second order in the field as predicted by Kohn (1957) from symmetry considerations. The Stark broadening of the acceptor absorption lines was attributed to an unresolved partial removal of degeneracy of the excited states. The absorption line broadening mechanisms (phonon, dislocation, concentration, ionized impurity) were determined from new halfwidth measurements, which corrected an earlier study (Colbow 1963). The ionized impurity broadening is caused by the screened Coulomb "internal fields" of nearby ionized impurities which are present in uncompensated samples at temperatures greater than 50°K. A new theory of this broadening contribution (Cheng 1966) is in reasonable agreement with experiment; the earlier theory of the same effect (Colbow 1963) is shown to be inadequate. The effects of compensation on the boron absorption spectrum were measured and attributed to the unscreened Coulomb fields of ionized impurities present because of the compensation. The properties of a weak new absorption line which appeared in the compensated spectrum are described.

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