Growth and characterization by X-ray diffraction of GaP/InP short-period superlattices

Abstract

X-ray diffraction was used to structurally characterize symmetrically strained GaP/InP short-period superlattices grown on GaAs(001) substrates by atomic layer molecular beam epitaxy. The possibility of growing highly strained semiconductors layers (with misfit values of -3.6% for GaP and 3.8% for InP with respect to GaAs) without relaxation by misfit dislocations is studied for the case of the GaP/InP material system. Three different types of superlattices were grown to study their structural properties: (GaP) N(InP) M ( N = 2, M = 2 or 3; N = 3, M = 3 or 4) with total thickness of 200–250 nm (set A), 50 nm (set B), and about 8 nm (set C). Superlattices of set C samples contain only 5–7 periods and are embedded between two Al 0.7Ga 0.3As cladding layers. Conventional θ-2θ and high-resolution X-ray diffractometry were used to determine the period of the superlattices, in-plane and perpendicular strains (ϵ ‖ and ϵ ⊥), chemical composition ( N, M) and relaxation status of the different layers. The X-ray interference effect technique was used for the first time to analyze GaP/InP superlattices. We discuss the possibilities and limitations of this technique applied to structures of this type. The agreement between experimental and simulated diffraction patterns is very good, indicating the high quality achieved in the growth of this highly strained material system.