No abstract

Optical spectra in quantum wells are in many cases strongly influenced by disorder. In particular, energy relaxation of correlated electron-hole pairs through disorder-induced localized states determines the position and shape of photoluminescence lines. By a Monte Carlo simulation approach the energy relaxation is studied and the temperature dependence of the spectral peak and the linewidth are determined for a variety of model systems in the steady-state situation. ͓S0163-1829͑98͒05643-4͔

Subject classification: 72.20.Ee; 72.80.Ng; S12Percolation approach is used to study the dc hopping conductivity and thermopower in systems with a Gaussian density of localized states typical for disordered organic materials. It is shown that the theoretical methods developed earlier for the description of hopping transport in disordered inorganic solids, such as amorphous semiconductors, can also be successfully applied to description of hopping transport in organic disordered solids, such as conjugated or molecularly doped polymers. Calculations within the percolation approach give results in excellent agreement with those obtained by using a more transparent, though less rigorous approach based on the concept of the transport energy.Introduction In various disordered inorganic and organic materials, the transport of charge carriers at low temperatures is related to incoherent hopping between localized states. While the development of theory for transport in inorganic disordered solids, such as doped crystalline semiconductors, mixed crystals, semiconductor glasses, amorphous and microcrystalline semiconductors, was logically consistent, the situation is different for disordered organic solids, such as molecularly doped polymers, conjugated polymers and organic glasses. Efficient theoretical methods have been developed for inorganic systems. Among the most successful methods, one can note the percolation approach and the approach based on the concept of the transport energy. However, these methods are rarely applied to organic systems. On the contrary, description of hopping transport in organic materials is often based on the ensemble averaging of hopping rates, which is known to be quite inappropriate for the description of hopping processes. Such situation is unsatisfactory, since the physics of hopping processes in organic and inorganic solids and the basic models for their description are rather similar [1,2]. In both cases it is assumed that the hopping rate of a charged carrier G ij between two localized states i and j with energies e i and e j separated by the distance R ij is determined by the standard expression [1]

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.

No abstract