Basic properties of ternary group III nitride compound semiconductor non-polar surfaces

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The development of novel semiconductor devices based on wurtzite structure group III nitrides cannot rely solely on the binary compounds, i.e. GaN, AlN, and InN, since only ternary (Al,Ga,In)N compounds offer the possibility to engineer the desired electronic/optoelectronic properties. In order to control device properties in a bottom-up fashion, a detailed microscopic and spectroscopic understanding of the fundamental properties and physics of the ternary group III nitrides semiconductor materials is necessary. A direct experimental access to these properties is, however, a rather difficult task, since only surface sensitive measurements can provide such microscopic and spectroscopic information with sufficient resolution and hence bulk properties are typically hidden by non-stoichiometric ad-layers on polar group III nitride surfaces. This can be avoided by investigating non-polar surfaces, which allow for probing both bulk and surface properties. In addition, they are technologically relevant for wurtzite structure nanowires. Therefore, we propose to investigate basic properties of ternary group III nitride compound semiconductor non-polar surfaces. The objectives are to determine (i) intrinsic surface states, their spatial localization and energy levels, as well as the surface band gaps, (ii) the physical origin of the Fermi-level pinning and (iii) of electron accumulation effects, (iv) the electron affinities for the different compounds, (v) the effect of lattice strain and (vi) of doping on the basic properties, (vii) a microscopic and spectroscopic investigation of the ternary alloys to determine clustering, fluctuations, ordering, as well as growth dependent effects, and finally (viii) the analysis of defects, such as threading dislocations, steps, interface misfit dislocations, and their extrinsic states. With such a comprehensive understanding the design of electronic/optoelectronic devices based on group III nitrides can be turned much more effective.