Yuriko Matsuo

Growth of GaN directly on Si(111) substrate by controlling atomic configuration of Si surface by metalorganic vapor phase epitaxy

The direct growth of a GaN epitaxial layer on a Si(111) substrate by metalorganic vapor phase epitaxy (MOVPE) was performed using a low-temperature (LT)-GaN buffer layer with no Al-containing intermediate layer (e.g., AlN or AlGaN). No deterioration in the Si surface caused by the reaction between Si and Ga vapor was observed. However, when there were Ga droplets on the surface, Ga and Si formed a Ga?Si alloy, which caused the generation of numerous holes on the surface by melt-back etching at high temperatures. In addition, it was revealed that the coverage of the LT-GaN buffer layer on Si was strongly affected by the hydrogen (H2) partial pressure in the carrier gas. Using nitrogen (N2) carrier gas, a complete coverage of the LT-GaN buffer layer could be achieved directly over the Si surface. These features can be explained by the facts that the Si surface is partially terminated by hydrogen atoms and the coverage of hydrogen on Si surface depends on H2 partial pressure.

Theoretical Investigation of Arsenic Desorption from GaAs(001) Surfaces under an Atmosphere of Hydrogen

We investigate the desorption of As from GaAs(001) surfaces under an atmosphere of hydrogen using the ab initio pseudopotential method. The GaAs surface is (2×4) reconstructed with arsenic-monohydrogen bonds, arsenic-dihydrogen bonds, and Ga–Ga dimer bonds. We propose a mechanism for As desorption from the (001) surface in the presence of ambient hydrogen. The calculated activation energy is close to the experimental value for the (1×1) to (2×4) transition according to an in situ gravimetric (GM) method.

Growth of MnGeP2 Thin Films by Molecular Beam Epitaxy

Epitaxial growth of the Mn-containing novel ternary compound MnGeP2 has been investigated. Prior to the growth experiments, theoretical studies using an ab initio calculation were carried out, on the basis of which the stable existence of MnGeP2 with a chalcopyrite structure was predicted. Growth experiments of Mn-Ge-P were performed on GaAs(001) and InP(001) substrates using a molecular beam epitaxy (MBE) technique, in which Mn and Ge were supplied from solid sources and P from a tertiary butyl phosphine (TBP) gas source. The optimum growth condition has been estimated on the basis of X-ray diffraction studies. Oriented overgrowth of MnGeP2 was confirmed from a reciprocal lattice mapping (RLM) on X-ray diffraction (XRD) analyses, and lattice constants have been determined to be a=0.569 nm and c=1.13 nm based on the assumption that the material has a tetragonal crystal structure.

Investigation of Hydrogen Chemisorption on GaAs(111)A Ga Surface by In Situ Monitoring and Ab Initio Calculation

Hydrogen chemisorption on the GaAs (111)A Ga surface is investigated under atmospheric pressure using an in situ optical monitoring system which consists of GaAs halogen transport atomic layer epitaxy (ALE) and surface photoabsorption (SPA) systems. The results of the in situ monitoring indicate the existence of a stable hydrogen-terminated surface. It is shown that hydrogen in the carrier gas reacts dissociatively with the (111)A Ga surface, and the relationship between the surface hydrogen coverage and hydrogen partial pressure is explained well by the Langmuir isotherm with dissociation. Atomic configuration on the surface is examined further by means of ab initio molecular dynamics calculation. The total energy change due to the calculated process is very close to the standard enthalpy of adsorption obtained by the experiment.

Ab initio Calculations of GaN Initial Growth Processes on GaAs(111)A and GaAs(111)B Surfaces

To understand the initial growth mechanism of GaN buffer layer on GaAs, the As desorption process from GaAs(111)A and GaAs(111)B surfaces was investigated by a first principle calculation method. The substrate orientation dependence of GaN buffer layer can be explained from the activation energies for As desorption processes.