A theoretical study of recombination at grain boundaries and surfaces in solar cells and quantum well lasers

The Shockley-Read recombination statistics was recently generalised to include the effects of a finite relaxation time of the captured carrier as it settles into the ground energy state of the trap, Auger effects and the so-called extra carriers supplied by the neighbouring material. The combined result of these effects is studied here theoretically at a surface together with consideration of a single trap energy level and a simple trap spectrum. This model of surface trap occupation is utilised in calculations of the potential barriers at grain boundaries in poly- crystalline semiconductors and these calculations are compared with some recent experimental results. The recombination rate at a grain boundary, resistivity and capacitance of polycrystalline semiconductors are studied, Another problem concerning the recombination of electrons and holes is found in quantum well laser diodes. It is suggested that the processes giving rise to radiation in quantum well heterostructures can be described by a no k-selection model for the electronic transition. The reason is contained in the similarity of experimental gain curves and those obtained using the no k-selection model, For lifetime measurements in solar cells, the minority carrier diffusion equation is solved. Results are given of treatments by Sturm- Liouville transform and Green's function for the excess minority carrier concentration in photovoltage decay and in the steady-state in mono- crystalline and polycrystalline semiconductors. The effects of surface recombination and grain boundary recombination on lifetimes in solar cells are examined using this theory,