A first step towards controlling and improving the quality of semiconductor devices is a deeper understanding of the fundamental mechanisms during doping and growth. For example, the morphology and structure of the surface controls the sharpness and thus the electronic characteristics of the interfaces, the incorporation of dopants or the formation of nanostructure such as quantum dots.

A challenge in performing simulations addressing these questions is the large range of relevant length and time scales. While eventually we are interested in a description on a mesoscopic scale (the size of typical quantum dots or surface features is in the order of 10..100 nm and the growth time is in the order of seconds) the mechanisms leading to these structures (adatom adsorption, diffusion, desorption, island nucleation) require a resolution in the length scale of 10^-1 nm and in the time scale of 10^-13 s^-1. Therefore, common approaches to simulate growth have been restricted on specific properties (on the mesoscopic scale) and included microscopic information only indirectly by empirical/adjustable parameters. In the present talk it will discussed how by combining density-functional theory with concepts of thermodynamics, continuum elastic theory, and/or statistical physics simulations can be performed which allow to bridge between microscopic and mesoscopic scales. To discuss the application but also the present limits of this approach we will focus on various issues regarding doping and growth of group-III nitrides (GaN, AlN, InN and their alloys).

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1. Sources of doping for InN bulk and surfaces
2. First ab initio determination of the phase transformations in Ni₂MnGa
3. Ab initio based growth simulations of group-III-nitrides
4. Ab initio based multiscale simulations of dislocations in GaN