A. V. Ankudinov

Specific features of the epitaxial growth of narrow-gap InSb quantum dots on an InAs substrate

Arrays of coherent InSb quantum dots (QDs) have been fabricated by liquid-phase epitaxy on InAs substrates in the temperature range T = 420–450°C. The QDs with a density of (0.9−2) × 1010 cm−2 were 3 nm high and 13 nm in diameter. A bimodal QD size distribution was observed, which was accounted for by a combined growth mechanism of these nanoobjects. Structural characteristics of a separate InSb QD formed on the InAs surface were studied for the first time by atomic-force and transmission electron microscopies. Moire fringes were observed for the first time for QDs in the InSb/InAs system, with the moire period of 3.5 nm corresponding to InSb QDs without an admixture of arsenic.

Cross-sectional atomic force microscopy of ZnMgSSe- and BeMgZnSe-based laser diodes

Atomic force microscopy (AFM) of cleaved facets of ZnSe-based lasers with various active region designs is reported. Different AFM probe friction on the materials forming the laser structures are exploited for imaging their basic layers. Unlike ZnMgSSe-based lasers, the cleaved surface of cladding layers in BeMgZnSe-based structures is atomically flat, which is attributed to hardening of the II–VI materials by Be incorporation. Nanometer-high steps and undulations are observed at the laser heterointerfaces on cleaved facets. The shape and height of such topographic singularities located in the vicinity of a (Zn,Cd)Se quantum well active region depend on the strain distribution in the laser waveguide.

Atomic-force microscopy of polarization domains in ferroelectric films

Single-crystal (001)-oriented PbZr0.47Ti0.53O3 and polycrystalline (111)-oriented PbZr0.47Ti0.53O3 thin ferroelectric films were studied using contact electrostatic force microscopy. Local electromechanical response measurements permitted study of the polarization vector distribution in natural and intentionally created polarization nanodomains in films. The principal components of an electromechanical response signal encountered in studies of ferroelectric films (the piezoelectric response and the additional capacitive contribution) were isolated and analyzed. The effect of tip-surface contact stiffness on the capacitive contribution to the electromechanical response signal was demonstrated experimentally and in terms of a model. It was shown that more accurate information on the distribution of the polarization vector in ferroelectric films can be gained by monitoring local variations in the tip-surface contact stiffness.

Optical Characterization of Synthetic Opals

The results of a structural-optical characterization of synthetic opals are presented. Information on the growth-induced features of the opal structure was derived from an analysis of the position and width of the one-dimensional photonic band gap. The structure of the samples was found to vary substantially along the growth axis coinciding with the [111] direction of the fcc lattice. It was shown that the regions corresponding to early stages in the opal structure growth are typically strongly disordered, which manifests itself, in particular, in the crystallites being misoriented relative to the sample growth axis. It was concluded that the regions of synthetic opals most suitable for application as photonic crystals are those corresponding to later growth stages.

Spreading resistance microscopy of polycrystalline and single-crystal ferroelectric films

Thin films based on lead zirconate titanate with stoichiometric composition near the morphotropic boundary have been studied using atomic-force microscopy methods. The dependence of the local conductivity on the local polarization direction has been observed for all samples, independently of substrate type, deposition method, and film thickness. It has been shown that the current response to the applied voltage exhibits a long current relaxation, about several tens of seconds, which is two to three orders of magnitude greater than the current relaxation time in an external circuit, associated with the ferroelectric domain switching. The conductivity features have been explained by recharging of traps localized at ferroelectric grain boundaries near electrodes and involved in polarization charge screening.

Growth and Characterization of InAs Quantum Dots on Silicon

We present a comprehensive investigation of molecular beam epitaxial (MBE) grown InAs quantum dots (QD) on silicon (001) and (111) by reflection high energy electron diffraction (RHEED) and Raman spectroscopy in UHV environment and ex-situ by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Two different ways were developed to prepare up to 10 11 cm -2 InAs QDs on Si(001). One is the conventional mode by exceeding a critical thickness of deposition at which 2D growth changes towards a 3D growth mode. A second way is a dewetting transition, induced by cooling an approximately I ML thin 2D InAs layer from growth temperature below a critical temperature at which RHEED indicates the formation of nanoislands. Samples grown in both manners show significant differences in morphology and shape though RHEED, TEM and Raman studies correspondingly indicate strain relaxation. On Si(111) InAs grows in the common temperature range for InAs growth (∼400°C) in flat clusters separated by deep trenches. A previous passivation of the Si(111) surface with arsenic at ∼700 °C on the other hand leads to the formation of large InAs nanocrystals.

On the accuracy of quantitative measurements of the local surface potential

The region of the main potential drop in a sharp p+−n+ junction in GaAs has been studied using the conventional and gradient scanning Kelvin probe force microscopy (KPFM) techniques. It is shown that the gradient method offers advantages for quantitative measurements. An algorithm for the program implementing the gradient KPFM method on standard commercial atomic-force microscopes is proposed. It is established that the layer of adsorbed water contributes to the measured width of the main potential drop region.

Dependence of the atomic structure and surface relief of platinum foils on the annealing and rolling conditions

The effect of cold rolling, polishing, and thermal annealing conditions on the atomic structure and surface geometry of platinum foils has been studied. The surface morphology has been analyzed using low-energy electron diffraction, atomic force microscopy, and scanning tunneling microscopy. The chemical composition of the surface has been evaluated by Auger electron spectroscopy. It has been demonstrated that a variation in the conditions used for the preparation of the samples makes it possible to produce surfaces with different degrees of perfection from atomically smooth to rippled, fractal, and diffraction-disordered surfaces.

Optical characterization of natural and synthetic opals by Bragg reflection spectroscopy

The Bragg reflection of light from natural and synthetic opals was studied experimentally, and the samples were characterized by atomic-force microscopy. The reflection spectra were theoretically calculated within the model of a planar, periodically layered medium. A comparison of the experimental and calculated data made it possible to determine the parameters of the crystal structure of synthetic opals (lattice constants and sintering coefficients of a-SiO2 particles). It was concluded that the pores in the structure of natural opals are filled by a material with a refractive index close to that of a-SiO2.

Kelvin Probe Force Microscopy of Hole Leakage from the Active Region of a Working Injection-Type Semiconductor Laser Diode

A method that enables direct observation and quantitative characterization of carrier leakage from the active region of working semiconductor light-emitting diodes and lasers is developed on the basis of Kelvinprobe microscopy. The method is used to reveal, on the surface of the mirror surfaces of high-power InGaAs/AlGaAs/GaAs laser diodes, minority holes arriving from the active region and spreading to the surface regions over the n-type emitter and n-type substrate. It is shown that holes can move through surface channels formed by regions of surface band bending to distances of tens of micrometers from the place where they originally appear at the surface. It is demonstrated that, as the injection current increases, the amount of leakage gradually grows and stabilizes after the onset of lasing.