S. G. Konnikov

Electronic structure of self-assembled InAs quantum dots in GaAs matrix

Capacitance–voltage characteristics have been measured at various frequencies and temperatures for structures containing a sheet of self-assembled InAs quantum dots in both n-GaAs and p-GaAs matrices. Analysis of the capacitance–voltage characteristics shows that the deposition of 1.7 ML of InAs forms quantum dots with electron levels 80 meV below the bottom of the GaAs conduction band and two heavy-hole levels at 100 and 170 meV above the top of the GaAs valence band. The carrier energy levels agree very well with the recombination energies obtained from photoluminescence spectra.

Electrochemical pore formation mechanism in III-V crystals (Part II)

Chemical and electrical processes developing at the semiconductor-electrolyte interface under conditions of anodic polarization were analyzed. It was shown that dense chemisorption coatings are formed on the surface of III–V crystals at voltages of pore formation onset, and a degenerate inversion layer is formed on the semiconductor side. In this case, a drop of the largest part of the applied voltage in the adsorption layer creates the prerequisites for nucleophilic substitution reactions involving chemisorbed anions and coordination-saturated atoms under the crystal surface. The mechanisms of these reactions were considered as applied to sphalerite-structured crystals. The results of experimental studies of the structures and compositions of porous layers in III–V crystals formed in various electrolytes at various polarization voltages are explained on the basis of the obtained concepts.

Unstrained epitaxial InxGa1−xAs films obtained on porous GaAs

Epitaxial layers of InGaAs solid solutions were grown on porous GaAs(100) substrates by liquid-phase epitaxy. A comparison between the compositions and thicknesses of these epitaxial layers with those of layers obtained under the same conditions on normal monolithic GaAs substrates suggests that the crystallization of epitaxial layers on porous substrates may be considered as the growth of free unstrained films.

Specific features of epitaxial-film formation on porous III–V substrates

Porous GaAs (100) and (111) substrates with nanostructured (∼10 nm) surface profiles are obtained in which pores branching in the 〈111〉 direction form a dense network with a volume density of ∼60% under the surface at a depth of ∼(50–100) nm. The surface of the substrates and the structure of GaSb layers grown on these substrates are studied. A decrease of 22% in the lattice-parameter mismatch at the GaSb/GaAs(porous) interface compared with that at the GaSb/GaAs(monolithic) interface is observed. Ideas about the chemical mechanisms of pore formation in III–V crystals are developed, and relations connecting the structure of porous layers to the composition of electrolytes and anodization conditions are established. It is shown that the dependence of the layers’ growth rate on lattice elastic strain can be conducive to an enhanced overgrowth of pores and to a transition to planar growth.

Growth of cubic GaN by molecular-beam epitaxy on porous GaAs substrates

It is shown that GaN layers can be grown on (100)-and (111)-oriented porous single-crystal GaAs substrates by molecular-beam epitaxy with plasma activation of the nitrogen by an rf electron cyclotron resonance discharge. The resulting undoped epitaxial layers possessed ntype conductivity with a carrier concentration ∼1018. Data obtained by scanning electron microscopy and cathodoluminescence indicate that at thicknesses ∼2000 Å, continuous layers of the cubic GaN modification are obtained regardless of the substrate orientation.

Electron escape from self-assembled InAs/GaAs quantum dot stacks

Abstract Capacitance–voltage characteristics have been measured at various frequencies and temperatures for a Schottky barrier structure containing three sheets of self-assembled InAs quantum dots in an n-GaAs matrix. By changing the frequency of the measuring signal at fixed temperature, it is possible to control the ratio between the thermionic and the tunnel contributions to the electron escape from the quantum dots. An applied magnetic field reduces the thermionic emission rate and increases the importance of the tunnel part of escape of electrons from the dots due to the deepening of electron level in the dots by Landau quantization in the GaAs conduction band.

Statistical analysis of AFM topographic images of self-assembled quantum dots

To obtain statistical data on quantum-dot sizes, AFM topographic images of the substrate on which the dots under study are grown are analyzed. Due to the nonideality of the substrate containing height differences on the order of the size of nanoparticles at distances of 1–10 μm and the insufficient resolution of closely arranged dots due to the finite curvature radius of the AFM probe, automation of the statistical analysis of their large dot array requires special techniques for processing topographic images to eliminate the loss of a particle fraction during conventional processing. As such a technique, convolution of the initial matrix of the AFM image with a specially selected matrix is used. This makes it possible to determine the position of each nanoparticle and, using the initial matrix, to measure their geometrical parameters. The results of statistical analysis by this method of self-assembled InAs quantum dots formed on the surface of an AlGaAs epitaxial layer are presented. It is shown that their concentration, average size, and half-width of height distribution depend strongly on the In flow and total amount of deposited InAs which are varied within insignificant limits.

Bistability of charge accumulated in low-temperature-grown GaAs

Capacitance–voltage characteristics were studied at various temperatures for Schottky barriers formed on n-GaAs/low-temperature-grown (LT)-GaAs/n-GaAs sandwich structures. Charge accumulation at deep traps in the LT-GaAs layer was observed. At room temperature, the C–V characteristics were found to be step-like with a wide plateau originated from emission of electrons accumulated in the LT-GaAs layer. At the temperature below 100 K, the electron emission from the LT-GaAs layer was completely suppressed. At intermediate temperatures (150–200 K), an effect of charge bistability was observed, which manifested itself as a hysteresis in the capacitance under sweeping the reverse dc bias. We suppose that the phenomenon takes place when the sweeping rate is higher than the electron emission rate but lower than the electron capture rate by the deep traps in the LT-GaAs layer.

Multiperiod quantum-cascade nanoheterostructures: Epitaxy and diagnostics

Advances in the production technology of multiperiod nanoheterostructures of quantum-cascade lasers with 60 cascades by molecular-beam epitaxy (MBE) on an industrial multiple-substrate MBE machine are discussed. The results obtained in studying the nanoheterostructures of quantum-cascade lasers by transmission electron microscopy, high-resolution X-ray diffraction analysis, and photoluminescence mapping are presented.

Local triboelectrification of an n-GaAs surface using the tip of an atomic-force microscope

The method of scanning Kelvin-probe microscopy is used to show that the effect of triboelectrification is observed when the tip of an atomic-force microscope interacts with the surface of n-GaAs epitaxial layers. The sign of the change in the potential indicates that the sample surface after triboelectrification becomes more negative. The observed specific features of the phenomena can be attributed to the thermally activated generation of point defects in the vicinity of the sample surface due to deformation caused by the tip.