Determination of local crystal quality characteristics and of the orientation of CdTe semiconductor films by nonlinear optical methods

Abstract

We study the phase space structure and the quantization of a pointlike particle in (2 + 1)-dimensional gravity. By adding boundary terms to the first-order Einstein-Hilbert action, and removing all redundant gauge degrees of freedom, we arrive at a reduced action for a gravitating particle in 2+1 dimensions, which is invariant under Lorentz transformations and a group of generalized translations. The momentum space of the particle turns out to be the group manifold SL(2). Its position coordinates have non-vanishing Poisson brackets, resulting in a non-commutative quantum spacetime. We use the representation theory of SL(2) to investigate its structure. We find a discretization of time, and some semi-discrete structure of space. An uncertainty relation forbids a fully localized particle. The quantum dynamics is described by a discretized Klein-Gordon equation.

New recombination centers in MBE MCT layers on (013) GaAs substrates

“…The average power of the exciting SH (second-harmonic) YAG : Nd laser varied in the range from 0.01 to 0.07 W. The standard time for obtaining an experimental diagram of the angular dependence of the SH signal ranged from 10 to 30 s. The diameter of the probed area was 200 µm at the generation depth of SH ∼ 5 nm. It should be noted that in the SHG method, a comparative quantitative analysis of experimental and numerical model data for an ideal crystal in a given local region allows us to obtain quantitative information about the crystal state of the near-surface layer of the sample under study [36][37][38]. Thickness measurements of the crystal state of the MCT layers were carried out with successive layer-by-layer chemical etching in Br : HBr = 0.05 solution : 1 and measuring the azimuthal dependence of the SH signal intensity.…”

Highly sensitive express nonlinear optical diagnostics of the crystalline state of heterostructures such as sphalerite

“…The calculation of the SHG signal intensity determined by the components of the nonlinear susceptibility tensor χ x y z (ω) in sphalerite class crystals (class 43m in international classification) is described in detail in [1,2]. For comparing the predicted data and experimental results of the SHG signal azimuthal dependences behavior in a specific geometry and for specific crystal slices, computer modelling [3,5,11] is applied.…”

“…When diagnosing semiconductor materials and structures that are transparent to the main radiation, the value of the registered reflected SHG signal at a given level of laser exciting radiation depends on the characteristics of the crystal, the perfection of its near-surface layer and on volume stresses (induced birefringence), the reflection of exciting radiation from the sample rear surface at the control point [3,5,11]. When studying the GaAs substrates and the CdTe buffer layers, given the strong absorption at the second harmonic frequency in those semiconductor materials transparent for the main radiation, it can be stated that the SHG signal corresponds to the point symmetry group of the near-surface layer crystal and can be thus used to characterize the structural quality of the 0.3−1 µm thick layer.…”

“…The dependence of SHG components polarization intensity on the mutual orientation of the exciting radiation polarization relative to the crystallophysical axes, when the SH polarization, parallel or perpendicular to the azimuthally varying linear polarization of the exciting radiation (further as the text goesangular or azimuthal dependence) is registered, allows obtaining quantitative information about the crystalline state of the surface layer, its orientation and several other properties while comparing experimental and model data in a given local area, to an accuracy less than or equal to a degree [1][2][3][4][5][6][7][8][9][10][11]. The diagnostic capabilities of the SHG method are widely used, for example, when studying the electronic and magnetic properties of materials by the characteristics the of identified magnetically induced second optic harmonic generation in diamagnetic and paramagnetic semiconductors [12,13].…”

“…Note that the SHG method allows obtaining data from a large area with high local resolution in the near-surface layer of the crystal [5,14], when moving a focused laser beam along two coordinates of the sample surface.…”