X-ray diffraction from low-dimensional structures

PbTe/SnTe superlattices were grown on ͑111͒ BaF 2 substrates by molecular beam epitaxy using PbTe as buffer layers. The individual layer thickness and number of repetitions were chosen in order to change the strain profile in the superlattices from completely pseudomorphic to partially relaxed. The superlattices structural properties were investigated by making reciprocal space maps around the asymmetric ͑224͒ Bragg diffraction points and /2⌰ scans for the ͑222͒ diffraction with a high resolution diffractometer in the triple axis configuration. With the strain information obtained from the maps, the ͑222͒ /2⌰ scan was simulated by dynamical diffraction theory. The simulated spectra of the pseudomorphic superlattices, in which the in-plane lattice constant is assumed to be the same as the PbTe buffer throughout the superlattice, fitted in a remarkably good agreement with the measured data, indicating that almost structurally perfect samples were obtained. For the thicker superlattices, the ͑224͒ reciprocal space maps revealed a complex strain profile. Our results show the importance of detailed structural characterization on the interpretation of the electrical properties.

Section: High Resolution X-ray Characterizationmentioning

confidence: 99%

Reciprocal space maps of PbTe/SnTe superlattices

Ferreira

Abramof

Rappl

et al. 1998

“…For this reason, the modeling of the rocking curve by a dedicated software using the generally accurate dynamical calculation for x-ray scattering is currently the most reliable method to extract structural information. 8 Fringes are not visible in the case of graded interfaces and cannot be seen in the simulated rocking curves calculated with the Fickian model (Fig. 2).…”

Section: Discussionmentioning

confidence: 92%

Concentration dependent interdiffusion in InGaAs∕GaAs as evidenced by high resolution x-ray diffraction and photoluminescence spectroscopy

Bollet

Gillin

Hopkinson

et al. 2004

A high resolution x-ray diffraction (HRXRD) and photoluminescence study of a 10 nm InGaAs/ GaAs quantum well structure repeatedly diffused under thermally accurate and timed annealing conditions demonstrates that the Fickian model with a constant coefficient of diffusion is inadequate and that the distribution of compositions of the diffused well cannot be fitted with error functions. A simple model, with the well retaining its square shape and homogeneity while dissolving the barriers when annealed, is successful in modelling both the HRXRD and photoluminescence data.

“…The independent variation of the two diffraction angles ͑between incident x-rays and sample surface͒ and 2 ͑be-tween incident and scattered x-rays͒ provides the possibility of reciprocal space mapping, i.e., the acquisition of twodimensional projections in the three-dimensional reciprocal space. 6,7 The lateral macroperiodicity of the wire and dot arrays gives rise to lateral intensity maxima ͑wire satellites W i and dot satellites D i ) in the diffraction pattern. In principle, the full information about the geometrical shape ͑height, width, inclination of the sidewalls, period͒ as well as about the structural quality ͑strain and crystalline damage͒ can be obtained from a two-dimensional map of reciprocal space.…”

Section: Methodsmentioning

confidence: 99%

Shear strains in dry etched GaAs/AlAs wires studied by high resolution x-ray reciprocal space mapping

Darhuber

Bauer

Wang

et al. 1998

We have fabricated GaAs/AlAs quantum wires and quantum dots by means of molecular beam epitaxy, electron beam lithography, and subsequent reactive ion etching using SiCl 4 and O 2 . The nominal periods are 300 nm and 350 nm for both wire and dot samples. High resolution x-ray reciprocal space maps of the 350 nm samples exhibit not only satellites corresponding to a periodicity of 350 nm but also additional satellites corresponding to a period of three times 350 nm, whereas there are no such extra peaks in the maps of the 300 nm samples. These secondary satellites are shown to be associated with a discretization effect in electron beam writing. Moreover, we found, that the shear strain in the wires has a distinct influence on the intensities of these weak extra satellites. Hence, they provide a sensitive means for the assessment of shear strains in elastically relaxed quantum wires.