Theory of InN surfaces
The recently acquired ability to grow high-quality InN, covered extensively in other chapters of this volume, has caused a surge in experimental studies of InN since the year 2000. Very few of the experimental studies have explicitly addressed structural aspects of InN surfaces, but it has been universally observed that high electron concentrations are present on the surface [13.3-13.6]. In this chapter, an overview of theoretical information that has been obtained on InN surfaces is presented. Most of this information has been derived from first-principles calculations based on density functional theory. Such calculations have become established as a powerful tool for studying surface reconstructions of semiconductors. A number of such calculations have indeed been performed for GaN surfaces by various groups; some of these will be cited at appropriate points in the text below. For InN, to our knowledge the only studies that have been published are by Großner et al. [13.7], Gan and Srolovitz [13.8] and by Segev and Van de Walle [13.9, 13.10]. The study of Großner et al. [13.7] was limited to investigations of In adlayers on a zincblende (111) 1×1 surface and concluded that formation of such adlayers is indeed favorable under In-rich conditions. Gan and Srolovitz [13.8] investigated wurtzite
(0001) and (0001¯) surfaces. Segev and Van de Walle covered a broader range of surface reconstructions on various surface orientations of wurtzite InN, and not only addressed atomic structure but also the electronic structure of the surface, a feature that is extremely relevant in the case of InN. The results will be discussed in detail below.