Tsunenori Sakamoto

Intensity oscillations of reflection high‐energy electron diffraction during silicon molecular beam epitaxial growth

Reflection high‐energy electron diffraction (RHEED) intensity oscillations during Si molecular beam epitaxy (MBE) are observed for the first time. It is revealed that stable RHEED intensity oscillation exists during the MBE growth of a single‐element semiconductor. The stable oscillations were observed only after preheating treatments. The substrate temperatures for the oscillation were from as low as room temperature to 1000 °C. One period of the oscillation corresponds to atomic‐layer or biatomic‐layer growth on the concerned surface. Oscillation of more than 2200 periods (∼6000 A) was observed. One oscillation period can be as slow as 38 min.

Si(001)-2×1 Single-Domain Structure Obtained by High Temperature Annealing

Si(001)-2×1 single-domain structure has been observed by reflection high-energy electron diffraction (RHEED) after a substrate annealing at a temperature of 1000°C for 20 min. This implies surface steps have been changed from monatomic layer to biatomic layer height by the annealing. It was found that the single-domain 2×1 surface structure is a necessary condition to observe stable RHEED intensity oscillations on the Si(001) surface during the growth.

Phase-Locked Epitaxy Using RHEED Intensity Oscillation

Long lasting RHEED oscillations during MBE growth of GaAs and AlxGa1-xAs are observed. Using these oscillations, accurate measurements of GaAs, AlxGa1-xAs growth rates and the Al mole fraction x were performed during the growths. The phase of the RHEED oscillations was analyzed by computer and molecular beam shutters were operated at a particular phase. This computer controlled phase-locked epitaxy (PLE) was applied to grow precisely defined (GaAs)2(AlAs)2 bi-layer superlattices. Raman scattering spectra showed split lines characteristic of superlattices. This PLE method is invulnerable to molecular beam fluctuations.

Layer‐by‐layer sublimation observed by reflection high‐energy electron diffraction intensity oscillation in a molecular beam epitaxy system

Reflection high‐energy electron diffraction (RHEED) intensity oscillation during sublimation of GaAs is observed at high substrate temperatures above 690 °C. This post‐growth RHEED intensity oscillation suggests that the sublimation occurs layer by layer. One period of this oscillation precisely corresponds to sublimation of one monolayer. Aluminum arsenide acts as a sublimation stopper. The sublimation rate was measured accurately as a function of substrate temperature.

Reflection high-energy electron diffraction intensity oscillations during GexSi1−x MBE growth on Si(001) substrates

Reflection high-energy electron diffraction (RHEED) intensity oscillations during the heteroepitaxy of GexSi1-x on a Si(001) substrate were observed for the first time. The oscillation amplitude decreased rapidly during GexSi1-x growth due to the three-dimensional growth, which had a strong dependence on the Ge mole fraction. The layer thickness of GexSi1-x/Si strained-layer superlattices was controlled precisely by monitoring the RHEED intensity oscillation. The interface roughness of GexSi1-x/Si heterojunctions was examined by the observations of RHEED intensity oscillations and high-resolution transmission electron microscope images.

RHEED studies of Si(100) surface structures induced by Ga evaporation

Abstract Si(100) surface structures induced by Ga molecular beam deposition in an ultra-high vacuum have been investigated using a reflection high-energy electron diffraction system (RHEED). It has been found that the Ga evaporation of submonolayer thickness on a clean Si(100) 2 × 1 surface produces surface structures of Si(100) 3 ×2, 5 × 2, 2 ×2 and 8 × 1 sequentially in the temperature range from 350 to 680° C. The RHEED patterns and a two-dimensional phase diagram including five superstructures are presented.

Which Surfactant Shall We Choose for the Heteroepitaxy of Ge/Si(001)? –Bi as a Surfactant with Small Self-Incorporation–

While the effectiveness of surfactants in Si/Ge heteroepitaxial growth has recently been reported, their disadvantages of self-incorporation and poor surface morphology restrict their practical application. We propose Bi as a surfactant which overcomes these disadvantages. We demonstrate by means of reflection high-energy electron diffraction and secondary ion mass spectrometry (SIMS) that Bi is an effective surfactant for Si/Ge heteroepitaxy in preventing both 3D islanding and surface segregation of Ge, while the amount of Bi incorporated in the epitaxial layer is smaller than the detection limit of the SIMS instrument (<5×10 16 cm -3 ) and Bi can be removed easily by desorption at temperatures as low as 575 o C

Rheed intensity oscillations during silicon MBE growth

Abstract Reflection high-energy electron diffraction (RHEED) intensity oscillations during Si molecular beam epitaxy (MBE) were observed for the first time. Stable oscillations were observed only after pre-heating treatments. The substrate temperatures for the oscillation were from as low as room temperature to 1000°C. One period of the oscillation corresponds to atomic-layer or biatomic-layer growth on the concerned surface. Oscillation of more than 2200 periods (≈ 6000 A) was observed.

RHEED-intensity oscillations of alternating surface reconstructions during Si MBE growth on single-domain Si(001)-2×1 surface

Abstract We previously reported the first observation of RHEED-intensity oscillations of the specular beam during Si MBE growth on Si(001), which showed a monatomic-layer-mode oscillations or a biatomic-layer-mode oscillation depending on the electron-beam incident azimuth. We further investigated Si MBE on Si(001) using RHEED patterns. We found that the structure of the Si(100) substrate surface was changed from the usual two-domain (2×1+1×2) to a single-domain 2×1 after high-temperature annealing. The RHEED patterns from the 2×1 and the 1×2 reconstructed surfaces were observed alternately during the growth for the first time. This alternating growth explained the RHEED-intensity oscillations of the biatomic-layer mode.

Is the c(4×4) reconstruction of Si(001) associated with the presence of carbon?

With the increasing annealing temperature in ultrahigh vacuum, hydrogen-terminated Si(001) surface exhibit a (1×2) reconstruction around 500 °C, c(4×4) in the narrow range of 580–750 °C, and a weak SiC transmission pattern above 750 °C. The simultaneous disappearance of c(4×4) and the appearance of the SiC pattern suggest that the c(4×4) reconstruction is associated with carbon contamination. The carbon concentration of 2.5×1018 atoms/cm3 is insufficient for carbon atoms to be a component of the c(4×4) structure, and therefore the carbon must be having another effect. A consequence of this conclusion is that carbon is not responsible for C-type defects.