| Abstract [eng] |
Carrier transport and recombination processes play a key role in optoelectronic device operation and thus must be well understood. More and more attention is directed toward understanding how these phenomena work in disordered semiconductor systems. One example of such disordered semiconductor system would be ternary and quaternary group III nitride compounds. They are widely used in solid state lighting and solar cell technologies. However their lack of well matched substrates makes growing quality layers a great challenge. Up to this day, the quality of III nitride semiconductors in terms of crystalline defects remains poor. It is known that, generally, the higher defect density there is in the semiconductor, the worse efficiency a device, based on such semiconductor, has. Nevertheless, there are many cases reported in literature of III nitride compound quantum wells having internal quantum efficiency of more than 80% and external quantum efficiency of up to 50%. This is attributed to carrier localization effects that manifest in such semiconductors. Carrier localization happens due to the spatial bandgap fluctuations in III semiconductor compounds as different components constituting the semiconductor usually distribute non-homogeneously inside the crystal. Localized states therefore work like traps creating barriers for carriers preventing them from reaching non-radiative recombination sites, which increases the efficiency of such devices by a big margin. There are many experimental techniques to investigate the semiconductors, but to understand what really happens in disordered systems we need a whole new tool that is based on computer modelling. An attractive technique to model disordered systems is the kinetic Monte Carlo algorithm. The working principle of this method is largely based on statistical treatment of such largely random systems as disrodered semiconductors. In this work the Monte Carlo method is used to investigate carrier transport in a generalized disordered semiconductor with predefined physical properties. The aim of this work was to determine, how localization effects in a disordered semiconductor alter the parameters such as internal quantum efficiency, carrier lifetime and carrier diffusion length, as well as to understand in what way the influence of defects (precisely - dislocations) is different in a disordered system with dislocation in comparison to the situtation when localization is absent. The parameters varied in this model were localization depth, dislocation density and carrier mobility. For all cases, the quantum efficiencies, carrier lifetimes and diffusion coefficients were calculated, providing detailed information about the investigated system. |
