Temperature Dependence of Impact Ionization in Submicrometer Silicon Devices

Photomultiplication, initiated by both pure electron and pure hole injection, has been measured in submicrometer Si p⁺-i-n⁺ and n⁺-i-p⁺ diodes with intrinsic region thicknesses w between 0.1 and 0.8 mum, at temperatures between 15 and 420 K. A local analysis is used to extract the values of effective ionization coefficients. Values of bulk ionization coefficients, alpha and beta, are then deduced and parameterized in an extended form of Chynoweth´s expression to cover their dependence on both electric field and temperature. Multiplication at various temperatures can be recovered from these bulk coefficients by using a simple dead space correction. beta falls faster with temperature than alpha so that the ionization coefficient ratio, k=beta/alpha, decreases with temperature. Decreasing w reduces this temperature sensitivity, which is weaker than in GaAs, possibly because of the softer ionization threshold in Si