O. P. Pchelyakov

Normal-incidence infrared photoconductivity in Si p-i-n diode with embedded Ge self-assembled quantum dots

Room-temperature infrared photoconductivity in a single layer of Ge self-assembled quantum dots incorporated into silicon p-i-n diode is reported. An in-plane polarized photocurrent response with two bias controlled maxima at 2.9 μm and at 1.7 μm wavelength has been observed. The two kinds of absorption driven by reverse bias in opposite ways are ascribed to the intraband hole bound-to-continuum transition and to the interband excitonic transition.

Silicon-Germanium Nanostructures with Quantum Dots: Formation Mechanisms and Electrical Properties

The generally accepted notions about the formation mechanisms for germanium islands with nanometer-scale sizes in a Ge-on-Si system are reviewed on the basis of analysis of recent publications. The presence of elastic strains in the epilayers and in the three-dimensional Ge islands on Si is a key factor that not only initiates a morphological transition from a planar film to an island-containing film (the Stranski-Krastanov mechanism) but also influences the subsequent stages of the islands’ evolution, including their shape, size, and spatial distribution. In many cases, this factor modifies appreciably the classical mechanisms of phase-formation and their sequence up to the quasi-equilibrium coexistence of three-dimensional Ge nanoislands at the surface of the Si substrate. The methods for improving the degree of the ordering of nanoislands to attain the smallest possible sizes and large density of areal distribution of these islands are discussed. The published data on optical absorption in the multilayered Ge-Si systems with quantum dots are considered; these data are indicative of an anomalously large cross section of intraband absorption, which makes this class of nanostructures promising for the development of photodetectors of the infrared region of the spectrum. The results of original studies of electrical and optical properties of heterostructures that involve Ge quantum dots and are synthesized by molecular-beam epitaxy on the Si substrates are reported.

Molecular beam epitaxy of silicon–germanium nanostructures

Abstract The current status of the research in the field of synthesis and application of silicon and germanium-based nanostructures formed by the process of 3D island self-organization is reviewed in the present paper. There was an obvious conclusion that elastic deformations in epitaxial films and 3D islands are the key factor which is not only the reason of the transition from planar to Stranski–Krastanow mechanism of growth, but also influences the next stages of islands evolution including their shape, size and spatial distributions. There are many cases when this factor makes crucial changes to the classical set of phase-formation mechanisms right up to an equilibrium coexistence of islands on a surface. Various types of ordering were classified in the nanocluster systems under consideration: in cluster shape, in its size, in the distance between nearest islands, as well as ordering through vertical, i.e. in successively growing multilayer structures containing quantum dots. The results of recent original investigations of electrical and optical properties of self-assembled arrays of Ge quantum dots are presented.

Artificial GeSi substrates for heteroepitaxy: Achievements and problems

It is desirable to have a set of substrates which are based on Si and ensure growth of heterostructures with various lattice parameters in order to develop electronic devices composed of semiconductor materials whose epitaxial growth is reasonably well developed. Such substrates are typically referred to as artificial. In this paper, a comparative analysis of various methods for the fabrication of artificial substrates (heterostructures), in which the relaxation of stresses is based on the introduction of misfit dislocations, is performed. Based on published and new experimental data, the mechanisms for attaining a low density of threading dislocations in plastically relaxed films represented by heterostructures composed of GeSi and an Si buffer layer grown at low temperatures are analyzed. The problems and results of another group of methods for obtaining artificial substrates which gained favor recently and become known as “compliant” or “soft” substrates are discussed. The most important electrical parameters of Si and GeSi films grown on artificial substrates are considered.

In situ RHEED control of self-organized Ge quantum dots

Abstract In situ registration of high-energy electron diffraction patterns was used for constructing the diagram of structural and morphological states of the Ge film on the Si(100) surface. The following regions identified in the diagram: two-dimensional (2D)-growth, ‘hut’- and ‘dome’-clusters, ‘dome’-clusters with misfit dislocations at the interface. Variations in the lattice constants of the Ge film during the MBE growth on the Si(100) surface were determined. An increase in the lattice constant at the (100) surface was attributed to the elastic deformation at the stage of 2D growth and formation of ‘hut’-clusters and to the plastic relaxation for the ‘dome’-clusters. As a result, epitaxial silicon structures with germanium quantum dots of 15 nm base size at the density of 3×1011 cm−2 were synthesized. The total electron structure of the hole spectrum of Ge quantum dots in Si was established.

Experimental determination of the incorporation factor of As4 during molecular beam epitaxy of GaAs

Abstract The incorporation factor of arsenic during molecular beam epitaxy of GaAs using As 4 and Ga was experimentally determined. It was found that the incorporation factor of As 4 significantly exceeded the value 0.5 for a wide spectrum of growth conditions. In several cases it is close to unity. The relative sensitivity coefficient, η of the Bayard–Alpert ion gauge was defined for arsenic in the form of As 4 and As 2 .

Formation of zero-dimensional hole states in Ge/Si heterostructures probed with capacitance spectroscopy

Abstract Hole energy spectrum in Ge/Si(001) heterostructures grown by molecular-beam epitaxy are studied using capacitance spectroscopy at a temperature range of 4.2–300 K. We find that the formation of Ge islands as the effective film thickness exceeds six monolayers leads to the appearance of the zero-dimensional hole states associated with Ge quantum dots. Analysis of the capacitance–voltage characteristics of structures containing the quantum-dot ‘atoms’ and the quantum-dot ‘molecules’ reveals the Coulomb charging effect.

III-V Compounds-on-Si: Heterostructure Fabrication, Application and Prospects

While silicon and gallium arsenide are dominant materials in modern micro- and nanoelectronics, devices fab- ricated from them still use Si and GaAs substrates only separately. Integrating these materials on the large and cheep Si substrate has been the subject of enormous research efforts for the past three decades. This review attempts to systematize and generalize the current understanding of the fundamental physical mechanisms governing the epitaxial growth of GaAs and related III-V compounds on Si substrates. Different kinds of bonding as a very promising non-epitaxial method for III-V thin film integration on Si substrate are reviewed. Basic techniques available for improving the quality of such het- erostructures are described, and recent advances in fabricating of device-quality III-V-on-Si heterostructures and corre- sponding devices are also presented.

Surface processes and phase diagrams in MBE growth of SiGe heterostuctures

Abstract The recent results of development and application of MBE methods for direct growth (self-organization or spontaneous formation) of the heterostructures Ge x Si 1−x Si are discussed. The heterostructures involve nanoobjects confined in two- or three-dimensional quantum-sized boxes or wires. The influence of substrate temperature, film composition and thickness on the structure and the surface morphology of the growing film were studied. Particular attention was paid to the surface structure evolution of Ge x Si 1− x heteroepitaxial films growing on Si(111)7 × 7 and Si(001)2 × 1 substrates over a wide range of concentrations x and growth temperatures. The quantum-sized islands can be self-organized after achievement of the critical thickness of the pseudomorphic layer; the critical thickness can be calculated in terms of the Frank-van der Merwe theory (when the Stranski-Krastanov growth mechanism is achieved). It was shown that with respect to the electronic properties, such films demonstrate the behavior of quantum boxes in which a zero-dimensional electron (hole) gas is localized. A number of heteroepitaxial structures with Ge quantum boxes in a tunnel-thin Si layers are grown by MBE and investigated.

GeSi films with reduced dislocation density grown by molecular-beam epitaxy on compliant substrates based on porous silicon

To grow high-quality heteroepitaxial layers, we propose a compliant silicon substrate consisting of a thin epitaxial silicon film on a high-density porous layer as a membrane and an expansive low-density porous layer as a mechanical damper which shields the overlying layers from the massive wafer. GeSi films over the critical thickness have been grown by molecular-beam epitaxy on these substrates. Transmission electron microscopy analysis shows that Ge0.2Si0.8 films have no dislocations owing to just elastic strain relaxation whereas plastic flow in the pseudomorphic films that are being grown on conventional Si substrates occurs with generation of dislocations in a regular manner. The experimental data on porous silicon structure are presented in some detail and are briefly discussed in connection with substrate compliance.