A. V. Kolesnikov

Initial stages of Ge epitaxy on Si(111) under quasi-equilibrium growth conditions

The results of the structural and morphological studies of Ge growth on a Si(111) surface at the initial stages of epitaxy by means of scanning tunneling microscopy and high-resolution transmission electron microscopy are presented. Epitaxy of Ge has been performed in the temperature range of 300 to 550°C under the quasi-equilibrium growth conditions and low deposition rates of 0.001–0.01 bilayers per minute. The stages of the formation and decay of the nanoclusters as a result of the redistribution of the Ge atoms into two-dimensional pseudomorphic Ge islands before the formation of the continuous wetting layer have been experimentally detected. The positions of the preferable nucleation of three-dimensional Ge islands on the wetting layer formed after the coalescence of the two-dimensional islands have been analyzed. The c2 × 8 → 7 × 7 → c2 × 8 phase transitions due to the lateral growth of the islands and the plastic relaxation of the misfit strains occur on the surface of the three-dimensional Ge islands when their strain state changes. The misfit dislocations gather at the interface and two types of steps lower than one bilayer are formed on the surface of the three-dimensional islands during the relaxation process.

X-ray diffraction analysis of epitaxal film distortions on miscut substrates (001)

A method for determining the structural parameters of epitaxial layers by X-ray difractometry was developed. The proposed model allows us to analyze the triclinic distortions that arise in heterosystems with nonsingular orientations. Slew angles of dislocation film lattice GexSi1 − x with respect to Si substrate have been obtained.

Superstructure phase transitions in Ge on Si (111) at the initial stage of epitaxial growth

The surface phase transitions 7 × 7 → 5 × 5 for two-dimensional and c2 × 8 →7 × 7 and 7 × 7 → c2 × 8 for three-dimensional Ge islands epitaxially grown on Si(111) were found experimentally using scan- ning tunneling microscopy. The first two transitions are associated with an increase in the level of misfit strains, while the last is related to a decrease in the stress level during plastic relaxation.

Dependence of plastic relaxation in GaAs films on nucleation of the first as monolayer on Si(001) substrates

The structure of GaAs films grown on Si(001) vicinal substrates (6° rotation about 〈011〉 axis) formed in two ways of nucleation, As deposition on Si and substitution of Si monolayer by As monolayer, is studied. X-ray diffractometry is used to find that the rotation direction of a crystal lattice depends on the manner of nucleation. An optional model of the formation of film dislocation structures is proposed.

Structural state of Ge/Si heterosystems with (001), (111), and (7 7 10) interfaces

It is shown for (111) and (001) interfaces that at an identical degree of strain relaxation in semi-conductor epitaxial films, the ratio of distances D between neighboring dislocations is D(111)/D(001) = 1.5. This allows us to establish that dislocation interface (7 7 10) contains partial 90° Shockley dislocations lying in three directions of 〈110〉.

Influence of the Misfit-Dislocation Screw Component on the Formation of Threading Dislocations in Semiconductor Heterostructures

In heterostructures with the (001) interface and diamond and sphalerite crystal lattices, the total relief of mismatch stresses by introducing two mutually perpendicular arrays of 60° misfit dislocations (MDs) was shown to be possible only if their screw components were of the same type. In the opposite case, it was necessary to introduce additional MD arrays that increased the probability of formation of threading dislocations in an epitaxial film. When the process is nonoptimal and two mutually perpendicular arrays are introduced with opposite types of screw components, excess energy of long-range shear stresses is accumulated. Examples of nonoptimal introduction of misfit dislocations are the operation of the Frank-Read and Hagen-Strunk modified dislocation sources. The relaxation process was simulated and investigated experimentally.

Effect of long-range stresses on the structure of semiconductor heterosystems

The dependence between the misfit value of the interface layers f and the structural parameters of the misfit dislocations is obtained for arbitrary orientation of the interface of a semiconductor heterosystem subjected to the complete relaxation of misfit stresses. Such parameters are the distance Di between neighboring dislocations of the ith family and projection of the edge component of the Burgers vector onto the interface (bie). The number of families incorporated into the interface is determined by the orientation of the boundary and occurrence of the relaxation process. The role of specific cases of this expression for experimental and technological applications is discussed using the appearance of long-range shear and normal stresses in films with orientations of (001) and (111) as examples.

Optimal and Nonoptimal Misfit Stress Relaxation in a Semiconductor Heterosystem

Misfit stress relaxation processes in a semiconductor heterosystem are divided into optimal and nonoptimal. Depending on the type of a process and degree of its completeness, four variants of a uniform stress field are established and experimentally detected in the surface layer of an epitaxial film. The interaction between threading dislocations that favors the transformation of nonoptimal relaxation into optimal is investigated.

Plastic relaxation of GeSi/Si(001) films grown by molecular-beam epitaxy in the presence of the Sb surfactant

Plastically relaxed GeSi films with the Ge fraction equal to 0.29–0.42 and thickness as large as 0.5 μm were grown on Si (001) substrates using the low-temperature (350°C) buffer Si layer and Sb as a surfactant. It is shown that introduction of Sb that smoothens the film surface at the stage of pseudomorphic growth lowers the density of threading dislocations in the plastically relaxed heterostructure by 1–1.5 orders of magnitude and also reduces the final roughness of the surface. The root-mean-square value of roughness smaller than 1 nm was obtained for a film with the Ge content of 0.29 and the density of threading dislocations of about 106 cm−2. It is assumed that the effect of surfactant is based on the fact that the activity of surface sources of dislocations is reduced in the presence of Sb.

Stress relaxation by generation of L-shape misfit dislocations in (001) heterostructures with diamond and sphalerite lattices

Abstract The problem of generation of L-shape misfit dislocations (MDs) is investigated for (001) heterosystems with diamond and sphalerite crystal structures. These 60° MDs can be formed by modified Frank–Read dislocation sources as well as by Hagen–Strunk ones. The analysis shows that perpendicular dislocation lines included in L-shape MDs have different types of screw dislocation components (namely, left-screw and right-screw ones). As a result, the stress-releasing process tends to slow preventing further generation of L-shape dislocations and annihilation of threading dislocations (TDs). To minimize density of TDs and to form equilibrium plane MD networks at the final stage of stresses relaxation process, it is necessary to generate mutually perpendicular MD arrays with the same types of screw dislocation components.