Multiscale growth and doping simulations of nanostructured devices

为了优化/设计基于宽带隙半导体的纳米结构器件，关键在于：(1)理解和识别导致自组织的生长模式；(2)实现高掺杂浓度，这对激光器件实现高注入电流和良好接触尤为关键。最近的实验和理论研究表明，这两个问题往往是相关的：高掺杂浓度可以显著改变甚至开辟新的生长机制，表面的结构/形态对掺杂效率有显著影响。模拟这种类型的相互作用的一个挑战是相关长度和时间尺度的大范围。对于器件设计来说，有趣的特征是100 - 1000纳米（长度），而生长这些结构的时间是秒级的。然而，这些效应的起源在于表面上的原子过程，它需要在埃的长度尺度和皮秒的时间尺度上进行分辨率。为了弥合长度和时间尺度上的差距，我们将开发和应用一种多尺度方法，该方法将密度泛函理论与热力学概念和统计物理元素分层结合。基于这种方法，我们将研究各种掺杂/杂质对生长方式、表面形貌和纳米结构形成的影响。这些结果将用于项目II-1和II-2的实验分析，并将作为理论项目III-2和III-3的输入参数。

To optimize/design nanostructured devices based on wide-bandgap semiconductors it is crucial to (i) understand and identify growth modes causing self-organization and to (ii) achieve high doping concentrations which are particularly critical for laser devices to realize high injection currents and good contacts. Recent experimental and theoretical studies showed that these two issues are often related: High doping concentrations may significantly modify or even open new growth regimes and the structure/morphology of the surface has significant effect on the doping efficiency. A challenge in simulating such types of interaction is the large range of relevant length and time scales. The features interesting for device design are of the order of 100 - 1000 nm (length) and the time to grow these structures is of the order of seconds. The origin of these effects, however, lies in the atomic processes on the surface which requires a resolution in the length scale of Angstroms and in the time scale of picoseconds. In order to bridge the gap in length and time scales we will develop and apply a multiscale approach which hierarchically combines density functional theory with thermodynamic concepts and elements of statistical physics. Based on this approach we will study the effect of various dopants/impurities on growth mode, surface morphology and nanostructure formation. These results will be used to analyze the experiments of projects II-1 and II-2 and will serve as input parameters for the theory projects III-2 and III-3.