Photoionization of Electrons at Sulfur Centers in Silicon

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Abstract
The photoionization of electrons from sulfur centers in silicon has been measured by the photocapacitance transient technique. The photoionization cross section of electrons was found to be much greater than that of holes. In the photon energy range of 0.70–1.00 eV, the photoionization cross section of electrons from neutral sulfur centers is approximately 2×10−16 cm2, and the photoionization cross section of electrons from singly ionized sulfur centers fits a Lucovsky delta‐function potential model better than a scaled hydrogenic model. For photon energies above the threshold, there was no observable field dependences or temperature dependences; however, near the threshold, a large field and temperature dependence was observed. As the field was increased from 2.1×104 to 1.1×105 V/cm, the threshold was lowered by approximately 0.01 eV. This reduction in threshold is much lower than predicted by a Poole‐Frenkel barrier lowering model. For photon energies below the threshold, there was evidence of a photothermal process.