Modeling of the atomic structure and electronic properties of highly mismatched Amorphous GaNAs alloys

A dramatic restructuring of the electronic bands of GaNAs alloys which can provide an almost perfect fit to the solar spectrum makes this material uniqe. Additionally, the amorphous nature of this alloy offers the opportunity to design low-cost, high efficient multijunction solar cells using a single ternary alloy system. However, the electronic properties of this material cannot be explained by the the theoretical models like virtual crystal approximation or forced quadratic fitting using a single bowing parameter. The aim of this thesis work is to model and investigate the properties of atomic and electronic behaviours of amorphous GaNAs alloys. For this goal, we have constructed structural models via molecular-dynamics simulations and continuous random network (CRN) methods. The nuclear positions were fully relaxed for all these generated models using density functional theory calculations. The analysis of network topology has been achieved by examining partial-pair correlation functions, bond angle distributions, ring statistics and average coordination numbers. The electronic properties of a-GaNAs alloys have been estimated by means of electronic density states and inverse participation ratios (IPR). We then compared their structural and electronic properties with band anti-crossing (BAC) model and experiments. We have shown that a clear band gap which is similar to the experimental results could be obtained by CRN model which is at the same time computationally less expensive and reliable in comparison to other methods. The study of EDOS and IPR also proves that the obtained band gap are in good agreement with the experimental results and BAC model.