Atomic level characterization and property control of surface and interface in nitride semiconductor heterostructures

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In this project, atomic-level characterization was carried out in order to understand GaN heteroepitaxy1. Construction of UHVMBE-SPMIn order to characterize and control III-nitride MBE growth in atomic level, new As-free UHVMBE-STM/AFM, which is capable of atomic-resolution imaging of insulators, was constructed.2. Growth of GaN on Si(111) and its polarity controlThe effect of Ga/N flux ratio on the polarity of GaN directly grown on Si(111) was studied by the STM imaging of Ga-rich reconstructions. We found that the N-rich growth condition at nucleation stage is critical for mono N-polar GaN growth.3. Formation of metal-GaN contactMetal-Ga alloyed structures which appear upon depositing metals on GaN(0001) were studied by STM. In the case of Au, c(2x12) was formed, and in the case of Ag, ultrathin film was formed. The ultrathin Ag film was unstable at room temperature, which indicates that the possibility of forming a good ohmic contact is low.4. Halogen etching of GaNEtching process of GaN was studied by exposing GaN(0001) to Cl, and observe the surface before and after annealing using STM. In the case of Ga-terminated surface, the etching proceeds bilayer-by-bilayer, and either step-edge etching or terrace etching was observed depending on the annealing temperature.5. Growth of GaN on Si(111) via ZrB_2 buffer layerZirconium diboride is recently attracting attention as a buffer layer for GaN growth on Si. The surface structure of thin ZrB_2 film epitaxially grown on Si(111), and the growth process of GaN on it was studied using STM and AFM. We found that N-polar GaN grows regardless of the growth conditions, and that the origin of mono-polarity is the stableness of GaN(0001)-ZrB_2(0001) interface of N-polar GaN and Zr-terminated ZrB_2.