Piezospectroscopic study (78°K) of radiation- produced absorption bands in Si†

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Abstract
A detailed study has been made on two sharp sub-bands, 3.45 μ (2900 cm−1) and 3.61 μ (2765 cm−1) of the 3.3 μ broad defect absorption band in irradiated Si. Our results indicate that the 3.45 μ and 3.61 μ bands are observed in all types of Si (n-, p-type, and intrinsic) subjected to fast neutron reactor irradiation. Spectra were measured at 78 °K under the effect of a variable uniaxial compressive stress with polarized light. A relatively large dichroism is observed for all three stress directions ⟨100⟩, ⟨110⟩, and ⟨111⟩. We also confirm that both sharp bands exhibit splitting and energy shifts under the action of stress. The model of the divacancy defect given by Watkins and Corbett(5) has been utilized to explain the data. The dichroism can be accounted for by the effects of Jahn-Teller alignment which arises from the strong bonding of nearest neighbor atoms of the divacancy. The splittings of the bands are small indicating that the Jahn-Teller distortion is little altered in the ground and excited states. The splittings appear to be most sensitive to stress along the vacancy-vacancy axis and a tentative model for the transitions is given.