In Situ TEM Study of Size-Controlled Bi Quantum Dots in an Annealed GaAsBi/AlAs Multiple Quantum Well Structure

An in situ transmission electron microscopy study of Bi quantum dot (QD) formation in an annealed GaAsBi/AlAs multiple quantum well (MQW) structure is presented in this work. The investigated structure, containing two GaAsBi QWs and embedded in an AlGaAs parabolic quantum barrier (PQB), was grown on semi-insulating GaAs (100) and was transferred onto an in situ heating holder (DENS solutions) and heated up to 650 °C. Sample evolution was continuously recorded in situ in bright-field STEM mode. The analysis revealed that QD formation occurs at lower annealing temperatures in case of in situ heating of lamella than in bulk. In addition, we find that the mechanism governing Bi QD formation is different in the in situ TEM experiment compared to bulk ex-situ annealing. Comparison of the ex-situ and in situ annealed structures, as well as in-depth postannealed structure TEM analysis, is presented.