Digital model for X-ray diffraction with application to composition and strain determination in strained InAs/GaSb superlattices

Abstract

We propose a digital model for high quality superlattices by including fluctuations in the superlattice periods. The composition and strain profiles are assumed to be coherent and persist throughout the superlattice. Using this model, we have significantly improved the fit with experimental X-ray diffraction data recorded from the nominal InAs/GaSb superlattice. The lattice spacing of individual layers inside the superlattice and the extent of interfacial intermixing are refined by including both (002) and (004) and their satellite peaks in the fitting. For the InAs/GaSb strained layer superlattice, results show: (i) the GaSb-on-InAs interface is chemically sharper than the InAs-on-GaSb interface, (ii) the GaSb layers experience compressive strain with In incorporation, (iii) there are interfacial strain associated with InSb-like bonds in GaSb and GaAs-like bonds in InAs, (iv) Sb substitutes a significant amount of In inside InAs layer near the InAs-on-GaSb interface. For support, we show that the composition profiles determined by X-ray diffraction are in good agreement with those obtained from atom probe tomography measurement. Comparison with the kinetic growth model shows a good agreement in terms of the composition profiles of anions, while the kinetic model underestimates the intermixing of cations. V C 2014 AIP Publishing LLC.

Detection of nanoscale embedded layers using laboratory specular X-ray diffraction

“…12,13 These models incorporate effects of interfacial roughness, interdiffusion at the interfaces, strain, and/or the presence of buffer and top layers, allowing characteristic properties to be evaluated. 12,13 To distill the key underlying physics governing the scattering of X-rays from regions such as those shown in Figure 1(c) in our intergrowth samples, we utilize a simplified optical model comprised of multiple parallel reflecting planes (Figure 2). For a "perfect" multilayer, diffraction can be modeled by letting each of the inter-planar distances be equal to the same value d (d B ¼ d A ), representing the repeat period of the intergrowth.…”

Peak separation method for sub-lattice strain analysis at atomic resolution: Application to InAs/GaSb superlattice

“…This result can be interpreted as the evidence of the Sb segregation into InAs during the growth, which was supported by the atom probe tomography result as well as X-ray diffraction. 31 Secondly, d is much larger than the lattice constant of pure GaSb, which indicates a compressive strain in the nominal GaSb layer. This can be attributed to In segregation into GaSb due to the large lattice constant of InSb (6.4794 Å).…”

“…33 Away from the interface, where the low frequency Fourier components dominate, the relaxation penetrates deeper and will behave as a relaxed thin film if t where t is the sample thickness. To examine the thin-film relaxation effect, we have separately determined the superlattice strain by X-ray diffraction 31 . and composition-correlated strain model (CCSM), respectively.…”

“…In FSM, the displacements of all 7 GaSb monolayers and 3 InAs monolayers near each interface are adjusted during fitting, while in CCSM the distance between two neighboring atomic layers are considered as an alloy structure and calculated using Vegard's law. 31 The X-ray fitting results shown in Fig. 7 were obtained using a smoothing filter, which averages the stain value at each point with two adjacent data points with a weight of 0. than that of GaSb at 6.0959 Å, thus InAs experiences a small tensile strain when it is grown epitaxially on the GaSb substrate and the out-of-plane lattice constant of the strained InAs is expected to be 6.0174 Å.…”

“…The presence of In in the nominal GaSb is also confirmed by our previous APT analysis. 31 Another notable feature is the tensile strain near the interfacial regions, which arises from the GaAs-like bonds. The tensile interfacial strain is seen by FSM and CCSM at the GaSb-on-InAs interface and the InAs-on-GaSb interface, respectively, while both are observed by atomic resolution imaging.…”