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The influences of hydrogen atoms on Ge heteroepitaxial growth on Si(111) surfaces using solid phase epitaxy (SPE) have been investigated by scanning tunneling microscopy (STM). In the SPE growth of Ge films on H-terminated Si(111) surfaces, the formation of 3-dimensional (3D) Ge islands are suppressed. With the desorption of H atoms, the 3D islands appear on the Ge surface, which are considered to be formed by the agglomeration of Ge atoms. The density of the islands is decreased and the size of the islands is increased by the existence of Si-H bonding at the Ge/Si interface. These phenomena are considered to be caused by the release of the stress in the Ge film and the weakening of the interaction between the Ge film and the Si substrate by Si-H bonding. In addition, the activation energy of the migration of Ge atoms during the agglomeration is determined to be 0.3 eV.

Surface reactions of H2O-adsorbed Si(100) with atomic hydrogen and oxygen have been examined by high-resolution electron energy loss spectroscopy (HREELS). The surface with saturated coverage of H2O is terminated by H and OH species and the sticking probability of H2O is estimated to be 0.9. This surface is stable for the adsorption of molecular oxygen at room temperature. The presence of dissociation sites of oxygen molecules such as dangling bonds is considered to be essential to the oxidation of Si(100) surfaces. By the reaction of H2O-adsorbed Si(100) with atomic hydrogen, the uptake of oxygen atoms of Si-OH bonds into sites of Si back bonds occurs even at room temperature.

The initial oxidation processes of H-terminated Si(100)-1×1 surfaces have been investigated using high-resolution electron energy loss spectroscopy at room temperature and 300°C. It has been found that oxygen atoms adsorb on one of the two back-bond sites of a surface Si atom until the oxygen coverage is 0.4 and in the sequential oxidation process, other adsorption sites such as the other back-bond sites and/or Si-Si dimer-bond sites, become occupied by oxygen atoms. The structural relaxation in Si-O-Si bonds is observed when a surface Si atom has two Si-O bonds, and is considered to originate from the change in the force constant of Si-O bonds.

The oxide formation on Si(100)-2×1 surfaces at room temperature has been studied by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The change in electronic structures due to oxidation has been discussed based on the spatially resolved STS spectra. It was found in the initial stage of oxidation that the local density-of-states (LDOS) of back bond states and dangling bond sites decreases dramatically at the oxidation-induced bright protrusions. The STS spectra of the 2×1 region with an oxygen exposure of 4.5 L suggest that oxygen atoms adsorb on the back bond sites. At the average SiO2thickness of 0.4 nm, the surface states of Si(100)-2×1 vanish completely and the energy width of the gap near the Fermi level becomes very close to the band gap of bulk Si. In addition, the observed LDOS is spatially uniform in spite of the presence of bumps in the STM image. The STS spectra indicate the formation of the valence band and the conduction band of SiO2at the oxide thickness of 0.4 nm.

We have investigated the single-electron phenomena in p-Si hopping conduction systems with a gate electrode. The hopping conduction systems have been fabricated on Si(100) substrates by focused ion beam (FIB) implantation of Ga+ions with a beam diameter of 0.1 µ m. The samples show nearest-neighbor hopping (NNH) conduction below 30 K and the conductance is found to oscillate by changing the gate voltage in the NNH conduction region. From the period of conductance oscillation, the gate capacitance is estimated to be about 0.3-0.4 aF. The evaluated size of a dot based on the capacitance is close to the dimension of localized states in this hopping conduction system. A plateau is also observed in current-voltage characteristics between source and drain electrodes. It is considered that these phenomena originate from a Coulomb blockade and that the chain of localized hopping states acts as asymmetric multiple tunneling junctions.