arXiv subjects

Shiro Tsukamoto

Publications and source records attributed to Shiro Tsukamoto.

7 recordsLinked to original sources

arXiv2020

Reentrant behavior of the density vs temperature of indium islands on GaAs(111)A

We show that the density of indium islands on GaAs(111)A substrates have a non-monotonic, reentrant behavior as a function of the indium deposition temperature. The expected increase in the density with decreasing temperature, indeed, is observed only down to 160 °C, where the indium islands undertake the expected liquid-to-solid phase transition. Further decreasing the temperature causes a sizeable reduction of the island density. An additional, reentrant increasing behavior is observed below 80 °C. We attribute the above complex behavior to the liquid-solid phase transition and to the complex island-island interaction which takes place between crystalline islands in the presence of strain. Indium solid islands grown at temperatures below 160 °C have a face-centered cubic crystal structure.

cond-mat.mtrl-sci↗

arXiv2019

Metal Droplet Effects on the Composition of Ternary Nitrides

We investigate effects of metal droplets on the In incorporation in InGaN epilayers grown at low temperature (450 C) by plasma assisted molecular beam epitaxy. We find a strong reduction of the In incorporation when the surface is covered by metal droplets. The such reduction increases with the droplet density and the droplet surface coverage. We explain this phenomenonology via a model that considers droplet effects on the incorporation of In and Ga adatoms into the crystal by taking into account the combined effects of the higher mobility of In, with respect to Ga, and to the vapor-liquid-solid growth that takes place under the droplet by direct impingement of nitrogen. The proposed model is general and can be extended to describe the incorporation of adatoms during the growth of the material class of ternary compounds when droplets are present on the surface.

physics.app-ph↗

arXiv2017

Droplet Controlled Growth Dynamics in Plasma-Assisted Molecular Beam Epitaxy of In(Ga)N Materials

We investigate the effect of the formation of metal droplets on the growth dynamics of InGaN by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) at low temperatures (T = 450°C). We find that the presence of droplets on the growth surface strongly affects the adatom incorporation dynamics, making the growth rate a decreasing function of the overall metal flux impinging on the surface as soon as the metal dose exceeds the critical amount required for the nucleation of droplets. We explain this phenomenon via a model that takes into account droplet effects on the incorporation of metal adatoms into the crystal. A relevant role is played by the vapor-liquid-solid growth mode that takes place under the droplets due to nitrogen molecules directly impinging on the droplets.

cond-mat.mtrl-sci↗

arXiv2010

Spatial Point Analysis of Quantum Dot Nucleation Sites on InAs Wetting Layer

We perform spatial point analysis of InAs quantum dot nucleation sites and surface reconstruction domain pattern on an InAs wetting layer, giving insights for quantum dot nucleation mechanism. An InAs wetting layer grown to 1.5 monolayers in thickness on a GaAs(001) substrate has been observed at 300 degC by using in situ scanning tunneling microscopy. The surface exhibits (1x3)/(2x3) and (2x4) reconstruction domains. A nearest-neighbor analysis finds that point pattern of quantum dot precursors was more similar to that of (1x3)/(2x3) domains which are specific to Ga-rich region. This provides the evidence that InAs quantum dot nucleation is induced by Ga-rich fluctuation within an InAs wetting layer.

cond-mat.mtrl-sci↗

arXiv2002

As-rich GaAs(001) surfaces observed during As4-irradition by scanning tunneling microscopy

As-rich GaAs (001) surfaces are successfully observed during As4-irradition by a system in which scanning tunneling microscopy (STM) and molecular beam epitaxy can be performed simultaneously. With a substrate temperature of 440 C and an As4 partial pressure of 2x10-6 torr, reflection high energy electron diffraction patterns and reflectance anisotropy spectra confirm a c(4x4) As-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that continual attachment / detachment of As molecules to and from the surface produces the observed dynamic behavior.

physics.chem-ph↗

arXiv2002

Structure analysis of the Ga-stabilized GaAs(001)-c(8x2) surface at high temperatures

Structure of the Ga-stabilized GaAs(001)-c(8x2) surface has been studied using rocking-curve analysis of reflection high-energy electron diffraction (RHEED). The c(8x2) structure emerges at temperatures higher than 600C, but is unstable with respect to the change to the (2x6)/(3x6) structure at lower temperatures. Our RHEED rocking-curve analysis at high temperatures revealed that the c(8x2) surface has the structure which is basically the same as that recently proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)]. We found that the surface atomic configurations are locally fluctuated at high temperatures without disturbing the c(8x2) periodicity.

physics.chem-ph↗

arXiv2002

Ga-rich GaAs(001) surfaces observed during high-temperature annealing by scanning tunneling microscopy

Ga-rich GaAs (001) surfaces are successfully observed during high-temperature annealing by scanning tunneling microscopy (STM). With a substrate temperature of 550 C, reflection high-energy diffraction patterns and reflectance anisotropy spectra confirm a (4x2) Ga-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that detaching and attaching of Ga adatoms may be the cause of these surface dynamics. For these conditions it is determined that zeta(4x4), zeta2(4x4) and zeta(4x6) reconstructions co-exist on the surface. The zeta2(4x4) reconstruction contains a Ga tetramer cluster and in more Ga-rich conditions, the zeta2(4x6) surface has a Ga octamer cluster.

physics.atm-clus↗