On the determination of the structural parameters of GaxIn1−xAs/AlAsySb1−y superlattices by X-ray diffraction

This work addresses the problem of a rapid determination by X-ray diffraction (XRD) of the structural parameters of superlattices (SLs) made by combining GaxIn1−xAs and AlAsySb1−y ternary alloys in view of quantum cascade laser (QCL) applications. It is first shown that due to the numerous parameters involved in such SLs, a single GaxIn1−xAs/AlAsySb1−y SL cannot be fully characterised by high-resolution X-ray diffraction (HRXRD). It is therefore proposed to use a double SL approach. This approach is shown to be an effective way to extract from a single HRXRD experiment the complete set of the structural parameters defining the SLs. However, some complications appear due to the additional strain in the structure that occurs under specific growth conditions favouring the formation of interfacial compounds. A careful examination of the coherence of the extracted structural parameters and of the detail of the growth procedure used at the SL interfaces can solve such problems. This is well exemplified here by the effect of the growth temperature: when it is increased, a coherent set of the SL structural parameters cannot be obtained without considering the strain associated to the As for Sb exchange arising at the GaInAs on AlAsSb interface.