Structural and Electronic Properties of the non-polar GaN (1-100) Surfaces
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Group-III nitrides attracted considerable interest due to their direct band gap, whose size is ideally suited for green to ultraviolet optoelectronics. One particular challenge of the epitaxial growth of these materials is, however, the impurity and dopant incorporation, which often depends on the position of the Fermi level at the growth surface. For non-polar GaN surfaces only little is known about the positions of the surface states and thus their possible influence on the Fermi energy. Therefore, we investigated the GaN (1-100) cleavage surface by scanning tunneling microscopy and spectroscopy and identified the energetic positions of the intrinsic surface states and the Fermi level. We found that both, the filled N-derived and empty Ga-derived dangling bond states are outside of the fundamental band gap. The observed Fermi level pinning of about 1.0 eV below the conduction band minimum is attributed to a high defect density at the surface, but not to intrinsic surface states.
Furthermore, the type, spatial distribution, the projected line direction, and electronic properties of dislocations in n-type GaN are investigated. Dislocations are found to form localized bunches of entangled nonparallel dislocation lines. Within these bunches uncharged perfect dislocations with a/3<11-20> Burgers vectors and negatively charged Shockley partial dislocations with a/3<1-100> Burgers vectors interconnected by a negatively charged stacking fault are found.
Lena Ivanova (PhD) received her Diploma degree and Ph.D. degree from the Technical University Berlin, Germany in 2005 and 2009, respectively, in Solid State Physics. Her research interests are in the areas of compound semiconductors and low-dimensional structures. She is currently working on non-polar GaN surfaces and InN/GaN heterostructures using scanning tunneling microscopy and spectroscopy.