Alexander M. Afanasev

Determination of the Photoelectron Emission Probability with Inclined X-ray Laue Diffraction

A simple relation has been established between the Fourier component of the probability density P(z) of photoelectron emission from different depths of a crystal and the angular dependence of the emission of photoelectrons formed in inclined X-ray Laue diffraction, which for the first time permitted the use of a direct method for the reconstruction of the P(z) function. Accurate measurements of the angular dependence of photoelectron emission were carried out on a silicon single crystal with diffraction of Cu K,~ radiation for different energy ranges. Photoelectrons were recorded by a proportional gas counter specially designed for the energy analysis of photoelectrons under inclined Laue diffraction conditions. The laws predicted by the theory have been fully confirmed, and the corresponding P(z) functions have been obtained.

Asymmetric X-Ray Diffraction

Abstract Physical phenomena characteristic of asymmetric X-ray diffraction schemes for perfect crystals, including diffraction under conditions of specular reflection, have been considered in detail. The principles underlying asymmetric crystal monochromators, achievements in obtaining narrow collimated X-ray beams, and the latest results on the application of asymmetric schemes in the investigation of thin subsurface layers are stated; along with the fundamentals of asymptotic Bragg diffraction, specific features of the grazing Bragg-Laue scheme and the analysis of amorphous sublayers with the use of the surface Bragg peak. Emphasis is placed on the application of asymmetric diffraction schemes in the method of X-ray standing waves to increase sensitivity (in recording of photoelectrons, fluorescence, and Compton scattering) and to study the characteristic features of the diffraction process in strongly asymmetric geometry.

Structural diagnostics of 'quantum' layers by X-ray diffraction and standing waves

We analyze the possibility for simultaneous adequate treatment of angular dependencies of the X-ray diffraction reflectivity and photoelectron yield (X-ray standing waves method) in order to extract the structural characteristics of semiconducting materials with ultra fine inclusions. Facilities of such an approach for evaluation of the degree of structural perfection of the layers, the phase shift of upper layers with respect to the buffer, the lattice parameters of particular layers and interfaces between them are demonstrated within the analysis of heterostructures based on the Si matrix with the Si1-xGex quantum wells and on the GaAs matrix with the InAs quantum dots.

XRD Study of Quantum-Well Heterostructures

Heterostructures implementing InAs quantum dots in a GaAs matrix are fabricated and examined by double-crystal XRD. Structural parameters of the layers and interfaces are evaluated. It is shown that the structural quality of the cap layer is affected by its doping level.

Al x Ga1 – xAs/GaAs/Al x Ga1 – x As Double Quantum Well with a Thin AlAs Interwell Barrier: Structural Characterization by SIMS and XRD

An AlxGa1 – xAs/GaAs/AlxGa1 – xAs double quantum well with a thin AlAs interwell barrier is examined by SIMS and double-crystal XRD for an AlAs thickness of about 10 or 18 Å. Thickness and other structural parameters are determined for each layer. The rocking curves are found to indicate a fairly abrupt interwell barrier.

In x Ga 1–xAs Strained-Layer Quantum Well in a Pseudomorphic Heterostructure: High-Resolution XRD Characterization for Different Quantum-Well Thicknesses

Strained-layer quantum wells of different thicknesses are realized in the form of an n-Al0.25Ga0.75As/InxGa1 – xAs/GaAs pseudomorphic heterostructure. The structural properties of the quantum wells are determined by high-resolution double-crystal XRD and by photoluminescence spectroscopy. The depth profile of In mole fraction is derived from the rocking curves. It indicates that the quantum-well interfaces are strongly smeared and hence their In mole fractions are less than the target value, 0.19. The XRD data are compared with the photoluminescence ones.

Characterization of a Quantum Well in an Si/Si1–xGex/Si Heterostructure by X-ray Diffractometry

Rocking curves with a pronounced pendulum-solution pattern are obtained for Si1 – xGex/Si specimens with a single quantum well (QW) by double-crystal x-ray diffractometry. These oscillations are typical of the rocking curves for GaAs multilayers with QWs. With Si–Ge multilayers, they are obtained for the first time. The Ge depth profiles of the QW are reconstructed from the rocking curves. As a result, the thicknesses of both QW interfacial layers are estimated.

Asymmetric monochromator in noncoplanar diffraction geometry

Abstract A strongly asymmetric noncoplanar diffraction scheme is suggested that provides a smooth variation of the asymmetry parameter over a wide range of values and reflections from various planes at arbitrary wavelengths with the use of only one standard crystal monochromator.

Photoelectron yield in x-ray grazing-incidence diffraction

Abstract Peculiarities of the photoelectron yield in conditions of X-ray grazing-incidence diffraction are discussed. The high sensitivity of photoelectron emission angular dependence on structural perfection of the crystal subsurface layers is demonstrated. A method for evaluation of the escape depths of photoelectrons with different energies is proposed.