Atomic-scale investigation and its device application for GaN crystal growth

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In this project, we have studied on the following subjects as listed below; (1) establishing the general principles for the surface energy minimization and surface reconstruction of GaN surface by MBE-STM (2) understanding the atomistic process for the dopant incorporation and defect formation in GaN epitaxial layers. (3) clarifying the effect of dopant incorporation on the surface electronic properties (4) clarifying the atomistic process in dry etching and its application for the device fabrication. Based on those results, atomic interaction, growth dynamics, surface energetics, strain, and surface/film electronic properties, etc. which are the fundamental process for device fabrication, have been discussed.We have performed systematic investigations of surface reconstructions on Wurtzite GaN(0001) by MBE-STM. Various reconstructions on the GaN(0001) surface are studied and based on the comparison between the STM observations and first-principles total energy calculations, we propose an adatom scheme for the basic 2x2 and 4x4 structures, and others as well. Also, in order to understand atomistic process underlying dry etching processes of Wurtzite GaN, which is of great important for device application, we have carried out STM study of thermally activated dry etching of GaN surface by Cl_2 molecules. Our extensive studies show that at low temperature (〜650C) the dominated etching of Ga-rich GaN(0001) is anti-step-flow etching. On the other hand, at the higher temperature(〜700C), triangular etching pits on terraces start to form. Its single-step depth implies the bilayer-by-bilayer etching.