Selective ion-channeling study of misfit dislocation grids in semiconductor heterostructures: Theory and experiments

Abstract

Planar dechanneling by networks of misfit dislocations was measured in a series of In x Ga 1Ϫx As/GaAs samples ͑001͒ grown by molecular-beam epitaxy. At the beginning of the strain-relaxation process the dechanneling probability exhibits different values for nominally equivalent ͑110͒ planes. At larger strain relaxation, the dechanneling probability saturates at a value around 1 2 as the beam-energy increases. In order to explain these results a new model for planar dechanneling by dislocations is proposed. This model is based on the harmonic approximation of the continuum potential but anharmonicity effects are taken into account. The perturbation to the harmonic oscillations caused by the lattice plane curvature around a dislocation is written in terms of a distortion function that depends only on the geometrical configuration of the channeling direction and of the dislocation line. This function is explicitly calculated for geometrical configurations relevant to the present samples allowing us then to solve the equation of motion. The results show that the dechanneling probability saturates at a level sensibly lower than 100% due to the quasiplanar distribution of dislocations. Without any adjustable parameter, the comparison between computed and measured dechanneling probabilities supplies dislocation density values in excellent agreement with those measured by transmission electron microscopy and in good agreement with results deduced from previous strain-relaxation data.

Strain modification of AlGaN layers using swift heavy ions

“…Even though GaN-based materials and devices have been investigated very rapidly and intensely, there have been very few reports concerning the elastic strain in GaN based materials, especially in AlGaN and InGaN films. RBS/channeling is a reliable, non-destructive and accurate method for determining the strain in heterostructures (9)(10)(11)(12)(13). The effects of swift heavy ions (SHIs) on the defects and strain are not understood in the GaN bulk epilayers.…”

Raman and AFM studies of swift heavy ion irradiated InGaAs/GaAs heterostructures

“…An enormous amount of work has been reported on the characterization of strain and the strain relaxation mechanisms of heterostructures grown beyond the critical layer thickness. The most suitable and well established techniques for such studies are high resolution XRD (HRXRD) [3][4][5], ion channelling [6,7], electron microscopy [8,9] and Raman spectroscopy [10][11][12][13]. Since the lattice dynamics are affected by stress-induced lattice deformation, the strain in epitaxial layers and its relaxation can be analysed through the evaluation of the phonon frequencies in the Raman spectrum.…”

Transmission ion channeling analysis of isolated 60° misfit dislocations

“…5,6, 18 Mazzer et al 19 derived analytical formulae for the lattice plane distortion due to each of the screw and edge compo- nents of 60°dislocations in their planar dechanneling backscattering study of heavily relaxed In x Ga 1−x As/ GaAs. A 60°d islocation with a Burger's vector b = ͑a /2͓͒101͔ and a line direction along ͓110͔ can be resolved into edge components b 1 = ͑a /4͓͒110͔ , b 2 = ͑a /2͓͒001͔, and a screw component b 3 = ͑a /4͓͒110͔, where a is the lattice parameter of silicon, equal to 0.543 nm.…”