Some aspects of the X-ray structural characterization of (Ga1−xAlxAs)n1(GaAs)n2/GaAs(001) superlattices

Synchrotron radiation has been used to obtain double-crystal X-ray rocking curves from inhomogeneous layers of GalnAs on InP at a range of wavelengths. The consistency of the lattice-parameter profiles deduced by simulating the rocking curves using the Takagi-Taupin equations is shown to be good. The computational method has been extended to calculate the rocking curves from relatively thick multilayer structures of GaA1As on GaAs grown by molecular beam epitaxy. This dynamical-theory approach permits the prediction of positions, heights and widths of major and satellite peaks. Results are in excellent agreement with experimental measurements, and by comparing experimental and calculated profiles the structural parameters of the layer can be deduced. The dynamical theory is particularly suitable for calculating the complete rocking curve especially where thick confining layers are present and the computational model is directly applicable to multilayers with varying layer thicknesses.

Section: Multilayer Structuresmentioning

confidence: 57%

Section: Multilayersmentioning

confidence: 99%

Simulation of X-ray double-crystal rocking curves at multiple and inhomogeneous heteroepitaxial layers

Hill¹,

Tanner²,

Halliwell³

et al. 1985

“…The main satellite reflection '0' was identified by combining information from the GaAs 004 and GaAs 115 reflections (Zaus, Schuster, Grbel & Reithmaier, 1991). This reflection corresponds to the average unit cell of the epitaxic layers forming the superlattice (Kervarec, Baudet, Caulet, Auvray, Emery & Regreny, 1984). Therefore, it can be used to determine the average lattice mismatch of the superlattice parallel and perpendicular to the substrate surface.…”

Section: Methodsmentioning

confidence: 99%

An improved deviation parameter for the simulation of dynamical X-ray diffraction on epitaxic heterostructures

Zaus¹

1993

X‐ray diffraction rocking curves of a strained‐layer superlattice structure have been measured at symmetric and asymmetric Bragg reflections and compared with simulated diffraction curves. The calculations are based on dynamical scattering theory. The experimental and theoretical curves exhibit a discrepancy with regard to the angular position of the higher‐order satellite reflections, which can be removed by introducing a new expression for the deviation parameter in the dynamical diffraction theory. The improved deviation parameter extends the range of validity of the two‐beam approximation, especially for asymmetric reflections with glancing exit geometry. Therefore, if the relaxation of strained‐layer heterostructures is to be determined by comparison with simulated rocking curves, only the improved parameter should be used.

“…Although they have been extensively described in a previous work (Kervarec et al, 1984) some characteristic diffraction features of superlattices will be briefly recalled here. A heterostructure built with a moderately strained superlattice grown on a nearly matched substrate gives an X-ray diffraction pattern which can be described as follows:…”

Section: Methodsmentioning

confidence: 99%

Imperfections in (Ga_1−xAl_xAs)n₁–(GaAs)n₂/GaAs supperlattices as observed by X-ray diffraction techniques

Petroff¹,

Sauvage‐Simkin²,

Bensoussan³

et al. 1987

Self Cite

Growth imperfections in (Ga1−xAlxAs)n1–(GaAs)n2/ GaAs superlattices, grown on GaAs(001) substrates, have been investigated by X‐ray diffraction techniques coupling image and rocking‐curve recording. The use of a synchrotron radiation source has enabled topographic images formed with very weak superlattice reflections to be obtained. The intensity distribution across the sample surface observed in such images has revealed two different types of superlattice defects: either overall gradients of both the average composition and period or islands showing different composition and period from the surrounding material. Since these parameters control the optoelectronic properties and particularly the gap value it is of primary importance to grow homogeneous samples and to have a technique able to detect inhomogeneities such as the ones described in the present work.