S. P. Moshchenko

The Investigation of Intermediate Stage of Template Etching with Metal Droplets by Wetting Angle Analysis on (001) GaAs Surface

In this work, we study metal droplets on a semiconductor surface that are the initial stage for both droplet epitaxy and local droplet etching. The distributions of droplet geometrical parameters such as height, radius and volume help to understand the droplet formation that strongly influences subsequent nanohole etching. To investigate the etching and intermixing processes, we offer a new method of wetting angle analysis. The aspect ratio that is defined as the ratio of the height to radius was used as an estimation of wetting angle which depends on the droplet material. The investigation of the wetting angle and the estimation of indium content revealed significant materials intermixing during the deposition time. AFM measurements reveal the presence of two droplet groups that is in agreement with nanohole investigations. To explain this observation, we consider arsenic evaporation and consequent change in the initial substrate. On the basis of our analysis, we suggest the model of droplet evolution and the formation of two droplet groups.

Critical phenomena in the β-(2×4) → α-(2×4) reconstruction transition on the (001) GaAs surface

The critical exponents of the β-(2×4) → α-(2×4) reconstruction phase transition on the (001) GaAs surface are determined experimentally. It is found that the phase transition is analogous to a van der Waals transition. The critical parameters Tc, Pc, and Θc have been measured experimentally. The mean field theory is applied, and three-parameter isotherms are obtained that agree with the experimental results at the following values of the parameters: Est = 0.36 eV, ΔE = 0.18 eV, and Ei = 0.134 eV. Precision measurements of the critical exponents β and δ are carried out. Their values β = 1/8 and δ = 15 indicate that the phase transition is truly two-dimensional.

Exciton-plasmon interaction in hybrid quantum dot/metal cluster structures fabricated by molecular-beam epitaxy

Hybrid structures consisting of InAs/AlGaAs quantum dots and In clusters on the surface separated by an AlGaAs spacer with a specified thickness are investigated. The enhancement of the photoluminescence signal in the long-wavelength region manifesting itself in the appearance of a new narrow emission line is observed. This line is absent in the control structure with a quantum-dot array and no metal clusters. It also disappears with increasing thickness of the dielectric spacer between the layers. These results are explained in terms of a model taking into account the resonance interaction of excitons in quantum dots with localized surface plasmons in metal clusters.

Role of lateral interaction in the homoepitaxy of GaAs on the (001)-β(2 × 4) surface

The homoepitaxy of GaAs on the (001)-β(2 × 4) surface during molecular beam epitaxy is considered as a twodimensional first-order phase transition from the lattice gas of adsorbed growth components to the two-dimensional crystalline phase. In the context of the mean field theory of phase transitions, the parameters of lateral interaction between filled cells of the lattice gas are determined. The causes for the completion of the growth of a particular monolayer (self-ordering) before the beginning of growth of a new monolayer are clarified. The oscillations observed in the reflection high-energy electron diffraction experiments support the conclusions of the suggested theory of the phase transition for homoepitaxy.

Asymmetric c(4×4) → γ(2×4) reconstruction phase transition on the (001)GaAs surface

The c(4×4) → γ(2×4) reconstruction phase transition on the (001)GaAs surface is studied experimentally. It is shown that it is a first-order phase transition. The phase transition is found to exhibit a highly asymmetric hysteresis. The difference between the direct and inverse runs of the hysteresis is explained in terms of the mean field theory of an adsorption-induced phase transition by the substantial contribution of lateral multiparticle interactions in the adsorbate.

Self-assembled Quantum Dots: From Stranski–Krastanov to Droplet Epitaxy

The results of investigation of InAs QDs in Al(Ga)As matrix grown by Stranski–Krastanov method and droplet epitaxy are presented. The atomic and energy structure of InAs/AlAs QDs was investigated in different growth conditions for Stranski–Krastanov method, and the coexistence of direct and indirect band structures is revealed. However, the lack of carrier transfer due to the low quality of a heterointerface and high concentration of nonradiative recombination centers is challenging. To overcome these problems, we used droplet epitaxy. As QD density in droplet epitaxy is determined by nucleation, we studied the initial stage of homoepitaxy in model system of GaAs to analyze nucleation processes. A proposed statistical approach is also very effective to describe InAs/GaAs QD formation in Stranski–Krastanov mode. The array of In metal droplets on the GaAs surface is studied as an initial stage of droplet epitaxy, and a model of droplet evolution is proposed. Indium dose dependence of QD properties reveals a critical phenomenon of a growth mode transition. Finally high-quality \( {\hbox{InAs/A}}{{\hbox{l}}_{{{0}{.9}}}}{\hbox{G}}{{\hbox{a}}_{{{0}{.1}}}}{\hbox{As}} \) QDs structures with a perfect heterointerface and high efficiency of the carrier capture from wetting layer to QDs were grown by droplet epitaxy.

Thermodynamic and kinetic aspects of reconstruction transitions at the GaAs(001) surface

A kinetic and thermodynamic analysis is carried out for reconstruction transitions on the GaAs(001) surface. It is shown that the transition from the As-stabilized (2×4)β2 to the Ga-stabilized (4×2)β2 structures under As4 flux is a nonequilibrium phase transition and occurs if a certain steady concentration of arsenic adatoms is attained on the surface. The transition is continuous and can be approximated by a three-parameter isotherm. The moving force of an adsorbate-induced transition is the stabilization energy for the (2×4)β2 phase accompanying the formation of arsenic dimers from arsenic adatoms. This energy is estimated. The features of the phase transitions occurring under the As4 flux and under desorption conditions for an amorphous-arsenic film are discussed.

Oscillation of the mirror and fractional RHEED reflections during homoepitaxy on the (2×4)-reconstructed GaAs(001) surface

Oscillations of the intensity of mirror and fractional RHEED reflections during homoepitaxy on the GaAs(001)-(2×4) reconstructed surface were studied. A considerable difference was observed in the patterns of intensity variation for the mirror and the fractional (0 1/4) and (0 3/4) reflections corresponding to the α and β phases on the reconstructed surface. A kinetic scheme of elementary processes occurring on the Ga(001) surface upon the homoepitaxial growth initiation is proposed. The activation energy for the nucleation process was experimentally determined (5-eV). It is shown that the temperature dependence of the probability of critical nucleus formation is determined by the desorption of As2 dimers.

Reconstruction transition (4×2) → (2×4) on the (001) surfaces of InAs and GaAs

Phase transitions involving various atomic configurations on the (001) surfaces of GaAs and InAs were studied by RHEED. A kinetic scheme of the interaction between the As4 flow and the surface is proposed and the main equations describing the transitions are modified so as to correspond to the As4 (rather than As2) flux. A model of the (4×2) → (2×4) transition is suggested for reconstruction of a layer of metal atoms with subsequent stabilization by the adsorption of arsenic atoms. A considerable difference of the surface transitions in GaAs from that in InAs consists in greater force constants (more rigid bonds) in the former case. A significant role in the continuous evolution from (2×4)β to (4×2) phase in GaAs belongs to metastable disordered phases.

As4 incorporation kinetics in GaAs (001) molecular-beam epitaxy

A kinetic model of epitaxial growth on a Ga-stabilized GaAs (001) surface from As4 and Ga beams is proposed. Elementary surface processes are studied: adsorption-desorption of As4, bimolecular reaction of As4*, and incorporation of As2chem in lattice sites. The model correctly describes the experimental results for the growth rate at low and high As4 pressures. The role of As4 desorption from the surface in the epitaxial growth of GaAs crystals is analyzed.