Minority carrier lifetime in silicon photovoltaics : the effect of oxygen precipitation

Single-crystal Czochralski silicon used for photovoltaics is typically supersaturated with interstitial oxygen at temperatures just below the melting point. Oxide precipitates therefore can form during ingot cooling and cell processing, and nucleation sites are typically vacancy-rich regions. Oxygen precipitation gives rise to recombination centres, which can reduce cell efficiencies by as much as 4% (absolute). We have studied the recombination behaviour in p-type and n-type monocrystalline silicon with a range of doping levels intentionally processed to contain oxide precipitates with a range of densities, sizes and morphologies. We analyse injection-dependent minority carrier lifetime measurements to give a full parameterisation of the recombination activity in terms of Shockley–Read–Hall statistics. We intentionally contaminate specimens with iron, and show recombination activity arises from iron segregated to oxide precipitates and surrounding defects. We find that phosphorus diffusion gettering reduces the recombination activity of the precipitates to some extent. We also find that bulk iron is preferentially gettered to the phosphorus diffused layer rather than to oxide precipitates

Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm

SPIN-DEPENDENT RECOMBINATION AT DISLOCATION DANGLING BONDS IN Si

La recombinaison dépendant du spin des porteurs libres par l'intermédiaire des liaisons pendantes dues aux dislocations est étudiée en fonction de la température et de l'intensité de la lumière sous des champs magnétiques de 0,04, de 3,3 et de 12,5 KOe. L'analyse des résultats conduit à proposer un modèle fondé sur le concept de recombinaison via les liaisons pendantes après une capture préliminaire sur des niveaux intermédiaires peu profonds dus probablement au potentiel de déformation de la dislocation.Spin-dependent recombination of free carriers via dislocation dangling bonds (DDB) is investigated as a function of temperature and light intensity in magnetic fields of 0.04, 3.3 and 12.5 kOe. On the basis of an analysis of the data obtained, a model of the effect is proposed in which use is made of the concept of recombination via DDB with preliminany carrier capture at the intermediate shallow levels due, presumably, to the deformation potential of the dislocation