AlAs as a Bi blocking barrier in GaAsBi multi-quantum wells: Structural analysis

Abstract

Crystallographic properties of AlAs barriers in GaAsBi-based multi-quantum well structures grown on GaAs substrates by molecular beam epitaxy (MBE) and migration-enhanced epitaxy (MEE) were studied. The quantum wells were grown at temperatures ranging from 160 to 350 °C. The width of GaAsBi quantum wells varied from 4 to 20 nm. The optimization of technological parameters for the growth of high crystalline quality AlAs barriers at low temperatures was performed. To explore the impact of high temperature treatment on crystal quality, surface roughness and chemical composition stability, ex situ rapid thermal annealing was performed at 650-750 °C for 180 s in nitrogen ambiance. The structural quality of AlAs barriers, the morphology and sharpness of the interfaces between GaAsBi quantum wells and AlAs barriers were studied by high resolution X-ray diffraction, atomic force microscopy and high resolution transmission electron microscopy, respectively. In this study it was demonstrated that MEE allows one to achieve higher crystal quality of AlAs barriers at much lower temperatures in comparison to MBE. The blocking of Bi out-diffusion from the GaAsBi quantum wells toward the surface was shown for both MBE and MEE grown AlAs barriers.

HRTEM Study of Size‐Controlled Bi Quantum Dots in Annealed GaAsBi/AlAs Multiple Quantum Well Structure

“…Our group has demonstrated that AlAs layers prevent Bi out-diffusion from GaAsBi layers during an annealing procedure, and allows to adjust size of the Bi QDs that form in the quantum wells by varying the well width. [10] This work extends our initial studies by performing in-depth structural and chemical analysis of the system, as well as a statistical analysis of the Bi QD size distributions. Earlier HRTEM studies reported formation of Bi nanoparticles from 7.6 to 22 nm in size in thick GaAsBi layers.…”

“…The latter process is accompanied by the formation Bi nanoparticles and reduction of Bi content in a surrounding GaAsBi layer. Our group has demonstrated that AlAs layers prevent Bi out‐diffusion from GaAsBi layers during an annealing procedure, and allows to adjust size of the Bi QDs that form in the quantum wells by varying the well width . This work extends our initial studies by performing in‐depth structural and chemical analysis of the system, as well as a statistical analysis of the Bi QD size distributions.…”

“…A successful epitaxial growth of AlAs and GaAsBi compounds even at temperatures lower than 300 C was demonstrated in our previous investigations. [10,17] GaAs (100) substrate was used for the growth of GaAsBi/AlAs MQWs. Prior to the growth, the native oxide was removed at 650 C under a high arsenic flux.…”

“…The MEE mode is favorable for the epitaxial growth at very low temperatures when the excess of arsenic atoms induces the formation of antisite defects. A successful epitaxial growth of AlAs and GaAsBi compounds even at temperatures lower than 300 °C was demonstrated in our previous investigations …”

Bismuth Quantum Dots in Annealed GaAsBi/AlAs Quantum Wells

“…Then, the growth was interrupted and the substrate temperature was lowered for a growth of GaAsBi QWs and AlAs barriers. Migration-enhanced epitaxy (MEE) mode was used for AlAs deposition at the following growth sequence: one monolayer (ML) of Al, 5 s interruption for a migration of group III atoms, then a supply of 1 ML of As [ 14 , 15 ]. Finally, the MQW structure was covered by 5 nm-thick GaAs capping layer.…”