Electronic and vibrational spectra of defects in neutron-irradiated silicon

Abstract

Silicon irradiated with fast neutrons exhibits a variety of infrared absorption, photoconductivity [1] and photoluminescence spectra [2] in the infrared. They have been attributed to photo-excitation and photoionization of carriers bound to vacancies, divacancies, and impurity-defect complexes. Local modes of impurity-defect complexes have been observed [3]. One-phonon density of states of the host crystal manifests itself in the first-order infrared absorption as well as the Raman effect, a consequence of the absence of the strict translational symmetry in the irradiated crystal [4,5]. Microscopic models are available for many of the defect centres. If silicon is subjected to slow-neutron irradiation, 30Si naturally present in 3.05% abundance, transmutes to ³¹P via the ³⁰Si(n,Y)³¹ Si → ³¹P+β ^- reaction. After eliminating the radiation damage produced during this neutron transmutation doping, homogeneously doped Si(P) is obtained. The electronic excitation spectrum of the phosphorus donors observed as a function of annealing is highly instructive in the context of the charged defects produced during the neutron transmutation process [6].