Photoluminescence in ͑GaIn͒͑NAs͒ quantum wells designed for laser emission was studied experimentally and theoretically. The observed temperature dependences of the luminescence Stokes shift and of the spectral linewidth evidence the essential role of disorder in the dynamics of the recombining excitations. The spatial and energy disorders can cause a localization of photocreated excitations supposedly in the form of excitons. Theoretical study of the exciton dynamics is performed via kinetic Monte Carlo simulations of exciton hopping and recombination in the manifold of localized states. Direct comparison between experimental spectra and theoretical calculations provides quantitative information on the energy scale of the potential fluctuations in ͑GaIn͒͑NAs͒ quantum wells. The results enable one to quantify the impact of annealing on the concentration of localized states and/or on the localization length of excitons in ͑GaIn͒͑NAs͒ quantum wells.

We compare the luminescence efficiency (i.e., room-temperature photoluminescence intensity), fluctuations in composition and thickness, degree of localization, and luminescence decay times of In0.37Ga0.63As0.983N0.017 quantum wells grown by molecular-beam epitaxy at different temperatures and annealed under a comprehensive variety of conditions. Luminescence efficiency is not directly coupled to structural nonuniformity or localization, and even three-dimensional growth is not detrimental by itself. In contrast, there is always a correlation between luminescence efficiency and nonradiative decay time. Therefore, the luminescence efficiency of InGaAsN quantum wells depends almost exclusively on the density of nonradiative recombination centers, while the influence of structural nonuniformity is negligible.

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The band offsets of InGaAsN single quantum wells with varying nitrogen and indium content were quantitatively determined by surface photovoltage measurements. The experimental data directly show the different effect of nitrogen on the valence and on the conduction band states. While the conduction band offset strongly increases with increasing nitrogen concentration, the valence band offset is only weakly affected. In contrast, indium influences the valence and the conduction band states in the same way: both the valence and conduction band offsets increase with increasing indium content. In particular, the conduction band offset varies with In content as in N-free InGaAs quantum wells.

We propose a method for an industrial characterisation of silicon wafers using a conctactless photoconductance instrument. The main difficulty is given by the character--istics of commercial Si wafers for PV in terms of lifetime and doping level. In our method we perform extraction of effective lifetime at all the injection levels we obtain. The shape of effective lifetime vs. injection level curve d e pends on both the material characteristics and the processing technology employed. We have found a good correlation between the wafer curve shape and the final characteristics of the solar cell obtained. The principal goal of the method is to enlarge the use of the conctactless photoconductance instrument to industrial characterisation and to have a method that can calibrate each processing step for the maximum efficiency.