T. V. Shubina

Broadening of submonolayer CdSe sheets in CdSe/ZnSe superlattices studied by x-ray diffraction

We present x-ray diffraction studies of a CdSe distribution profile along the growth direction in CdSe/ZnSe submonolayer superlattices (SLs) grown by molecular beam epitaxy. The performed theoretical simulations show that the shape of both (004)- and (002)-reflection rocking curves is very sensitive to the vertical CdSe distribution around the intended deposition yplanes. In particular, broadening of the CdSe submonolayer insertions results in a decrease in SL (±1) and (±2) satellite intensities. Comparison of the simulations and experimental data allows us to conclude that CdSe sheets in the as-grown SL samples are asymmetrically broaden up to 5 monolayers.

Bragg and Laue x-ray diffraction study of dislocations in thick hydride vapor phase epitaxy GaN films

The dislocation structure of hydride vapor phase epitaxial thick GaN layers grown on sapphire is studied by analysis of the microdistortion tensor components. Symmetrical reflections (including reflections from planes forming a large angle with the basal plane) with two modes of scanning (θ and θ–2θ) in two geometries (Bragg and Laue) are used to obtain the tensor components. The instant connections between the tensor components and major dislocation types are specified. Different types of dislocation distributions have been identified in the thick GaNfilmsgrown on sapphire with and without undoped and Si-doped metalorganic chemical vapor deposited templates. Transmission electron microscopy was used to confirm the x-ray results by direct visualization of defect rearrangements.

Determination of microdistortion components and their application to structural characterization of HVPE GaN epitaxial layers

The dislocation structure of hydride vapour phase epitaxial thick GaN layers grown on sapphire is studied by analysis of the microdistortion tensor components. Symmetrical reflections (including reflections from planes forming large angles with the basal plane) with two modes of scanning (θ and θ-2θ) in two geometries (Bragg and Laue) are used to obtain the tensor components. The instant connections between the tensor components and major dislocation types are specified. Different types of dislocation distributions have been identified in the thick GaN films grown on sapphire without and with undoped and Si-doped metal-organic chemical vapour deposited templates.

Optical and Transport Properties of CdSe/ZnSe Self-Organized Nanostructures: 1-Dimensional versus 3-Dimensional Quantum Confinement

We present comprehensive studies of optical, structural and transport properties of molecular beam epitaxy grown CdSe/ZnSe self-organizing nanostructures, aimed at elucidation of the intrinsic morphology of CdSe layers as a function of their nominal thickness (w). Particular attention has been paid to the layer thickness below the critical value (w < 3.0 monolayer (ML)). It is found that the layer morphology is transformed from pure two-dimensional objects at w<0.7 ML to extended (15–40 nm) flat islands formed in the thicker layers. The density of the islands increases with w, which is accompanied by enhancement of the luminescence quantum efficiency. An optically pumped green laser is fabricated, taking advantage of the superior emission characteristics of the single CdSe layer with w=2.8 ML, used as an active region. The threshold power density of 3.9 kW/cm2 observed at 300 K is fivefold less than that of the reference sample using a conventional ZnCdSe quantum-well active region.

MBE growth and properties of bulk BeCdSe alloys and digital (BeSe : CdSe)/ZnSe quantum wells

We report for the rst time on MBE growth, structural and optical properties of single layers, quantum well structures and short-period superlattices based on Be x Cd 1~x Se ternary alloys on GaAs. Both the conventional MBE growth mode and the sub-monolayer digital alloying technique (SDA) have been employed for the fabrication of the structures. Compositional boundaries of an instability region 0.03(x(0.38, calculated in a regular solution approximation for the completely coherent system, agree well with available experimental data. A suppression of the phase separation in BeCdSe by elastic stress in the layer, accompanied by a strong reduction of the Cd incorporation coe

Defect-induced island formation in CdSe/ZnSe structures

cient has been found. Ultrathin 2.8 ML BeCdSe SDA QWs with x&0.15 demonstrate about an order of magnitude increase in the PL intensity with respect to the pure CdSe one, probably resulting from an enhanced carrier localization e

Spatial distribution of Cd in CdSe/ZnSe superlattices studied by X-ray diffraction

ciency. E ’ as a function of the Be content reveals a strong bowing in optical data, which allows one to consider BeCdSe alloys with compositions nearly lattice-matched to GaAs as potential materials for the active region of blue-green lasers. ( 2000 Elsevier Science B.V. All rights reserved.

X-ray diffraction determination of the interface structure of CdSe/BeTe superlattices

Island formation in CdSe/ZnSe superlattice (SL) structures with a moderate defect density is investigated in a sub-monolayer range of CdSe nominal thicknesses. Besides the spontaneous formation of CdSe-enriched islands in defect-free regions, presence of dislocations crossing the SL causes an emergence of the defect-attached islands. The island location near interceptions of CdSe sheets with the dislocations produces a staircase ordering of the islands in neighboring SL layers. Such a mutual alignment of the CdSe-enriched islands results in modified optical properties of the defect-containing structures. Density and type of the defects promoting the laterally inhomogeneous incorporation of Cd are controlled, in general, by the initial stage of MBE growth and a lattice mismatch between ZnS(Be)Se cladding layers and a GaAs substrate.

Interface effects in type-II CdSe/BeTe quantum dots

Abstract Double and triple X-ray diffractomery was used for a structural characterization of the short-period superlattices (SLs) CdSe/ZnSe with submonolayer sheets of CdSe. The multilayer structures containing SLs were grown by molecular beam epitaxy (MBE) on (001) GaAs substrates. The period of SLs was in range (30–60 A), the nominal thickness of CdSe sheets varied from 0.2 to 1.2 monolayer. The parameters of SLs have been determined. Broadening of CdSe sheets in direction normal to interface has been revealed. Full width at half maximum (FWHM) of this broadening is equal to about 4.5 monolayers and does not depend on the period and content of Cd in SLs.

Electrically stable p-type doping of ZnSe grown by molecular beam epitaxy with different nitrogen activators

Structural study of CdSe/BeTe superlattices (SLs) grown by molecular beam epitaxy on GaAs substrate was performed by using double and triple crystal x-ray diffractometry. The period of the studied structures was about 5 nm, while the thickness of thin CdSe insertions varied from 0.4 to 1.5 monolayer. It is shown that new Be-Se bonds arise at the BeTe-CdSe interfaces in addition to the Be-Se bonds expected at the CdSe-BeTe interfaces. From the analysis of the diffraction curves of 002-reflection the complex composition of interfaces and thin insertions has been determined and contribution of all types of bonds in each SL period calculated. The diffraction curves of 004-reflection were used for the specification of the fine structure of the interfaces.