X-ray diffraction from CuPt-ordered III-V ternary semiconductor alloy films

Abstract

A model has been developed to describe x-ray scattering from CuPt-type ordered III-V ternary semiconductor alloys. The model takes into account the size distribution of the two different laminae-shaped variants, the random distribution of antiphase domain boundaries in each variant, and the atomic displacements due to the bond-length difference between the two constitutive binary materials. A synchrotron x-ray source was employed to measure the weak-ordering reflections from CuPt-ordered Ga 0.5 In 0.5 P and Al 0.5 In 0.5 As samples. By comparing the experimental results and the model calculations, structure information, including the average number of atomic layers in the laminae of each variant, the average antiphase domain size, and the average order parameter in each variant, were obtained. Results from single-variant films and poorly ordered films are also discussed.

Determination of the order parameter of CuPt-B ordered GaInP2 films by x-ray diffraction

“…␦ i is a complex function of s and can be obtained independently from a valence force field ͑VFF͒ model calculation. 12,14 For CuPt-B ordered GaInP 2 , we found that the difference in length between the In-P and the Ga-P bonds is mainly accommodated by the displacement of P atoms. The displacement of In and Ga atoms is significantly smaller.…”

“…13 Debye-Waller factors, which were deduced from the Debye temperatures of GaP and InP, were included in the atomic form factors. 12 The intensity of the ordering peaks increases as the order parameter increases. On the other hand, the relative intensity of the ordering peaks is modulated by atomic displacements.…”

“…13 These methods require either knowledge of fundamental reflections 5,11 or structural details of the ordered domains. 11,12 This makes the analysis complicated and less accurate, because the required information is often not readily accessible. For example, the fundamental reflections of an ordered film often overlap the substrate reflections because the film is usually designed to be lattice matched with the substrate.…”

“…However, until very recently, in most structural studies only a qualitative measure of the ordering information using words such as ''strong,'' ''medium,'' and ''weak'' was reported. [6][7][8][9][10] Attempts to obtain quantitative ordering information have, however, been made lately by employing sophisticated electron and x-ray diffraction techniques, 5,11,12 largely based on a 40-year old principle given, e.g., by Warren. 13 These methods require either knowledge of fundamental reflections 5,11 or structural details of the ordered domains.…”

Self-assembled chains of single layer InP/(In,Ga)P quantum dots on GaAs (001)

“…PL measurements suggest an atomic ordering in the ͑In,Ga͒P layer. In order to prove this model further x-ray scattering investigations on fractional Bragg reflections 34 and transmission electron microscopy measurements are planned.…”