Radiative recombination processes of thermal donors in silicon
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Radiative recombination processes of thermal donors in silicon S. Pizzini , S. Binetti, E. Leoni , A. Le Donne, M. Acciarri, A. Castaldini(*) INFM and Department of Materials Science, University Milano- Bicocca , Via Cozzi 53, Milano, Italy (*)INFM and Department of Physics, University of Bologna, Viale Berti Pichat 6/2, Bologna , Italy ABSTRACT There is a recent, renewed attention on the possible development of optical emitters compatible with silicon microelectronic technology and it has been recently shown that light emitting diodes could be manufactured on dislocated silicon, where dislocations were generated by plastic deformation or ion implantation. Among other potential sources of room temperature light emission, compatible with standard silicon-based ULSI technology, we have studied old thermal donors (OTD), as the origin of their luminescence is still matter of controversy and demands further investigation. In this work we discuss the results of a spectroscopical study of OTD using photoluminescence (PL) and Deep Level Transient Spectroscopy (DLTS) on standard Czochralsky (Cz) silicon samples and on carbon-doped samples. We were able to show that their main optical activity, which consists of a narrow band at 0.767 eV ( P line), is correlated to a transition from a shallow donor level of OTD to a deep level at EV+0.37 eV which is tentatively associated to C-O complexes. As we have shown that the P line emission persists at room temperature, we discuss about its potentialities to silicon in optoelectronic applications. INTRODUCTION It is well known that a long dwelling at temperatures around 450°C during the cooling cycle of large diameter, crucible grown, oxygen-rich Cz silicon or any thermal annealing of Cz silicon in the same temperatures range, leads to the generation of oxygen related donors, often referred as Old Thermal Donors (OTD), to distinguish them from other types of thermal donors that can be formed in the temperature range 600–700 °C and today known as New Thermal Donors (NTD). Since their discovery generations of investigators addressed their studies to the microscopic structure, the growth and decomposition kinetics as well as the electrical and optical properties of OTDs, using all the techniques suitable for the study of electrically and optically active, paramagnetic centres. In spite of many thousands (around 19000) of papers published on the topic, which make of the OTDs one of the most studied defect centres in semiconductors, and whose properties have been recently reviewed by Newman [1] a defect model which consistently explains all their features, including their optical properties, is still lacking. In fact, while it is well known that oxygen rich silicon annealed at 450 °C for several hours exhibits a prominent photoluminescence spectrum with a narrow no–phonon line at 0.767 eV, generally labelled P line [2], a direct proof that oxygen is incorporated in the centre has not yet been given. Furthermore, PL measurements have cast doubts on a simple relationship between thermal donor
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