Near-band-edge photoluminescence in doped silicon : an investigation of BMEC and DA pair processes

This thesis deals with the study of two types of radiative recombination in silicon : a) donor-acceptor pair recombination (DAPR) and b) bound mu1tiexciton complex (BMEC) recombination: a) DAPR Work. New sharp line structure in the 1.6 to 20 K, near-band-edge photo-luminescence of Si(P,In) has been identified as due to radiative recombination of electrons bound to P donors with holes bound to In acceptors. This work represents the first study of sharp line, DAPR luminescence in an elemental semiconductor. Straightforward analysis assuming only Coulomb interactions between otherwise isolated impurity centres indicates that recombination involving P and In centres separated by distances ranging from 7.7 to 20 Å is responsible for the sharp line structure, which is observed superimposed on the high energy shoulder of the distant (average P-In separation : ~ 55 Å) pair band. Transient measurements reveal a decay pattern consistent with that expected for DAPR luminescence. Annealing and intentional doping behaviour has also been measured . BMEC Work. The Zeeman spectra of the α¹ to α⁴ photoluminescence lines of Si(P) and the Li¹ to Li⁴ photoluminescence lines of Si(Li ) have been measured as a function of temperature in the range 1.5 to 4.2 K. As expected on the basis of the Kirczenow BMEC shell model (SM), the thermalization behaviour indicated by the Si(P) spectra differs substantially from that indicated by the Si(Li ) spectra. This is related to the different valley-orbit state ordering of the two systems. The observed Zeeman sub-structure and thermalization behaviour in both the Si(P) and Si(Li ) systems is shown to be in very good agreement with the predictions of the SM. Specifically, the SM predicts two unique effects: no low temperature thermalization for the Zeeman sub-components of α⁴ and the disappearance of all the Zeeman sub-components of Li¹ at the lowest temperatures; these effects have both, been observed, A direct measurement of the free exciton (FE) ground state splitting, based on the observation of a resolved splitting of the FE[sup TA] luminescence band is discussed briefly. The splitting is found to be ΔE = 0.31 (+ 0.03 , - 0.06) meV .Science, Faculty ofPhysics and Astronomy, Department ofGraduat