FRANCK-CONDON SHIFT AND TEMPERATURE-DEPENDENCE OF THE ZERO-PHONON BINDING-ENERGY OF THE DEEP SELENIUM CENTER IN SILICON

Using the steady-state photocurrent technique spectral distributions o f the photoionization cross section for holes of the deep selenium cen tre in silicon have been measured at 11 temperatures within the temper ature range 51 K less than or equal to T less than or equal to 297 K. A novel analytical model is proposed which properly accounts for the c ompeting ionization processes into the light- and heavy-hole valence b ands. Curve fittings based on detailed numerical calculations of convo lution integrals result in a Franck-Condon shift of about 27(+/-5) meV together with an effective phonon energy of about 34(+/-5) meV. The p artial shrinkage coefficient alpha(p)/alpha(cv) quantifying the shrink age of the zero-phonon binding energy for holes, J(p)(T), with respect to that of the bandgap was found to be about 0.93(+/-0.05), indicatin g an approximate pinning of the deep single substitutional selenium le vel to the conduction band edge. A hole binding energy of J(p)(0) = 57 7.2(+/-1) meV at T = 0 was obtained from an extrapolation of the fitte d J(p)(T) curve.