Yu. G. Galitsyn

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.

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.

2D AlN layer formation on (111)Si surface by ammonia MBE

An (0001)AlN ultrathin layer formation in ammonia MBE conditions have been investigated by RHEED. Two steps procedure was used: at first, well ordered (8×8) silicon nitride was prepared on the atomically clean Si surface under ammonia flux. Then AlN was formed by deposition of Al atoms onto the (8×8) surface. Temperature dependence of the AlN formation rate was obtained and desorption energy (Edes=2.1 eV) of Al atoms from the surface was estimated. For the first time the (4×4) superstructure of AlN on the (111)Si surface was observed by RHEED. Precise measurements of the AlN in-plain lattice parameter evolution during the initial stages of the AlN formation were carried out. The lattice constant of 3.08 A is found in good agreement with ab initio calculations for a graphene-like AlN.

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.

Effect of the Sapphire-Nitridation Level and Nucleation-Layer Enrichment with Aluminum on the Structural Properties of AlN Layers

The effect of atomic aluminum deposited onto sapphire substrates with different nitridation levels on the quality of AlN layers grown by ammonia molecular-beam epitaxy is investigated. The nitridation of sapphire with the formation of ~1 monolayer of AlN is shown to ensure the growth of layers with a smoother surface and better crystal quality than in the case of the formation of a nitrided AlN layer with a thickness of ~2 monolayers. It is demonstrated that the change in the duration of exposure of nitrided substrates to the atomic aluminum flux does not significantly affect the parameters of subsequent AlN layers.

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.

Commensurate and incommensurate indium phases on a (111)A InAs surface

Adsorption phases of indium on a (111)A InAs surface are investigated. Three phases are detected: (2×2)a, (1×1), and the (0.77×0.77) incommensurate phase. The (0.77×0.77) incommensurate phase is modeled as a densely packed (111) layer of In (fcc) crystal situated in epitaxial relation to the InAs substrate: 〈110〉In∥〈110〉InAs. Reasons for the realization of the fcc crystal structure are analyzed. It is shown that the incommensurate phase is spatially modulated by the periodic potential of the substrate. A comparison of our data on indium adsorption onto (111) InAs with the data in the literature on indium adsorption onto (111) Si, Ge reveals the importance of relaxation of the elastic strains in the formation of two-dimension adsorption-induced superstructures.