Kiyoshi Kawamoto

Quasi-Medium Energy Ion Scattering Spectroscopy Observation of a Ge δ-doped Layer Fabricated by Hydrogen Mediated Epitaxy

We have observed the behavior of Ge δ-doped layers in Si(001) by Quasi-medium energy ion scattering spectroscopy (Q-MEIS). The δ-doped layers were fabricated by hydrogen mediated epitaxy (HME) of Si. We found that, in the δ-doped layers fabricated by HME, the surface segregation of Ge atoms was reduced compared with that by conventional molecular beam epitaxy (MBE). The Ge atoms, however, were widely spread in the growing film. We assume that in the HME sample, hydrogen atoms are segregated to the top-most layer of the growth surface. Moreover, the Si buffer layer has a comparatively good crystalline quality in the HME sample.

Observation of the diffusion of Ag atoms through an a-Si layer on Si(111) by low-energy ion scattering

We have observed the behavior of Ag atoms at the interface between a deposited Si layer and an Si(111) surface using a recently developed ion-scattering spectroscopy. At RT deposition of Si, the Ag layer is anchored at the interface between amorphous and crystalline Si. With increasing annealing temperature, the Ag atoms were observed to diffuse out over the adsorbed a-Si layer. In addition, we indicate that the buried structure of the substrate is reflected by the multiple scattering component of the ion scattering spectrum.

A new apparatus for impact collision ion scattering spectroscopy

A new type of time-of-flight impact collision ion scattering spectroscopy apparatus is presented. The system mainly consists of a 20 kV Penning ion source, a beam chopper and an annular-type micro-channel plate. Ion beam energy can be changed in the range from 2 to 20 keV. Since the shadow cone radius can be varied meaningfully by selecting suitable acceleration voltage, it becomes possible to determine structures of subsurfaces or buried regions as well as of the topmost layer. We show that this apparatus enables us to observe layers as much as 10 layers below the topmost layer. In addition, we measured the shadow cone radius of 10 keV 4He+ incident on the Si(001) surface, and the result is compared with a calculated value.

Quasi-medium energy ion scattering spectroscopy observation of surface segregation of Ge δ-doped layer during Si molecular beam epitaxy

Abstract We have observed the behavior of Ge δ-doped layers fabricated by molecular beam epitaxy (MBE) on an Si(001) substrate and the surface segregation of Ge atoms from δ-doped layers during a top Si buffer layer growth using quasi-medium energy ion scattering spectroscopy. We have found that the Ge atoms segregate to the surface even at a low substrate temperature of 300°C. This result is in contrast to the solid phase epitaxy case where Ge atoms diffuse around the interface. For MBE growth, at a substrate temperature of 600°C, the surface segregation was reduced. The distribution of Ge atoms is widely spread in the subsurface region. This result indicates that the Ge atoms are incorporated in the Si buffer layer with mixing by Si atoms.

Atomic-hydrogen-induced self-organization of Si(111)√3×√3-In surface phase studied by CAICISS and STM

Abstract Using coaxial impact collision ion scattering spectroscopy (CAICISS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) techniques, we have investigated the interaction of atomic hydrogen with the Si(111)√3×√3-In surface phase at elevated temperatures and structural behavior of In clusters induced by the interaction. Upon atomic hydrogen interaction, SiIn bonds are broken and replaced by SiH bonds. As a result, the √3×√3 reconstruction is destroyed and small In clusters are formed on hydrogen-terminated Si(111)1×1 surface. Using STM, we also have found that the size of the In cluster increases with increasing substrate temperature during hydrogen exposure of the √3×√3-In surface phase. From CAICISS experimental results, we have found that atomic-hydrogen-induced In clusters for Si(111)√3×√3-In surface phase have an In(100) crystalline structure, while those for Si(001)4×3-In surface phase are polycrystalline. In conclusion, we have found that structural differences of surface give rise to different atomic-hydrogen-induced self-organization.

Laser-induced photoluminescence enhancement in a room-temperature emitting SiGe-based alloy quantum well

An enhancement of photoluminescence (PL) intensity was observed at room temperature in a SiGe/Si quantum well under continuous laser illumination. The laser-induced PL enhancement was found to be an irreversible process characterized by a time constant which decreases with increasing excitation power density. A modified defect reduction model based on recombination-enhanced defect reaction is invoked to interpret the PL enhancement in terms of an improvement in the crystal quality of quantum well layers induced by laser radiation.

In-situ observation of Ge δ-layer in Si(001) using quasi medium energy ion scattering spectroscopy

Abstract We have performed in-situ observation of Ge δ-layers in Si(001) fabricated by different methods, using quasi medium energy ion scattering spectroscopy. The following has been revealed: (1) the Ge atoms segregate to the surface even at a low substrate temperature of 200°C during MBE growth of Si buffer layer. (2) In the δ-layers fabricated by hydrogen mediated epitaxy, the surface segregation of Ge atoms was reduced compared with that by conventional MBE. The Ge atoms, however, were widely spread in the growing film. Hydrogen atoms are segregated to the topmost layer of the growth surface. (3) In a solid phase epitaxy (SPE) case, Ge atoms are confined and diffuse around the interface. For realizing δ-layer structure of doping atoms such as Ge, which are strongly segregated on the growth front, SPE is found to be an effective method.

Observation of behavior of Ge δ-doped layer in Si(001)

Abstract We have observed the behavior of Ge δ-doped layers in Si(001) by low energy ion scattering spectroscopy (LEIS). The stopping power of He in a-Si has been estimated to be about 9.5 eV/A, which is larger than the theoretically calculated stopping power. We found that, in the focusing direction, the yield due to the lattice atoms buried beneath ∼50 A can be regarded as similar to those in “random” directions without perturbation due to the focusing effect, as for Rutherford Backscattering Spectrometry (RBS). The Ge δ-doped layer fabricated by solid phase epitaxy (SPE) was found to be located at the interface. At an annealing temperature of 600°C, Ge diffused around the interface and alloyed with the Si atoms.

Behavior of Ge δ-doped Layer in Si (001) Observed by TOF-LIEIES

We have investigated a Ge δ-doped layer in Si(001) formed by solid phase epitaxy (SPE) using time-of-flight low-ener-gy ion scattering spectroscopy (TOF-LEIS). The Ge δ-doped layer was formed by annealing a Si buffer layer deposited on a Ge(1ML)/Si(001) surface. We found that Ge atoms diffuse from the δ-doped layer around the interface as a result of SPE growth of the Si buffer layer. Incident angle dependence of Ge and Si intensities at various annealing temperatures showed that the Ge atoms began to occupy Si lattice sites above 300°C; indicating Ge-Si alloying near the interface region, and that the diffusion of Ge atoms was promoted above 500°C accompanied by the crystallization process of the Si buffer layer. The thickness of the Si1-xGex layer at 600°C was estimated to be about 30 A, where the Si buffer layer was nearly perfectly crystallized.

Quasi-medium energy ion scattering spectroscopy study of Ge δ-layer on Si(001)

Abstract We have investigated a Ge δ-layer on Si(001) formed by solid phase epitaxy (SPE) using recently developed quasi-medium energy ion scattering spectroscopy (Q-MEIS). We found that SPE of a top Si buffer layer results in a diffusion of Ge atoms from the δ-doped layer around the interface. This result is in contrast with the molecular beam epitaxy (MBE) case where Ge atoms are segregated to the grown surface. The incident angle dependence of Si and Ge intensities shows that the diffused Ge atoms occupy the Si lattice sites, indicating the GeSi alloying near the interface region. Our results demonstrates that Q-MEIS is suitable for in-situ observation of buried layers during thin film growth processes.