InAs Quantum Dots

Abstract

In the following, TEM and PL measurements which reveal mass transport and segregation in InAs SK layers grown on GaAs(001) by MBE at growth temperatures of 480°C and 530°C are presented. Plan-view TEM reveals regularly shaped islands with a density of 7.8 × 10¹⁰ cm⁻² (480°C) and 1.5 × 10¹⁰ cm (530°C). Uncapped islands were investigated by strain state analysis of electron wave functions in the image plane, reconstructed from HRTEM images. Indium concentration profiles of the islands were obtained by measurement of lattice parameter profiles of the islands and application of FE calculations. We found that the islands contained Ga atoms with an average concentration of 50% (480°C) and 67% (530°C). The capped InAs layers were investigated by PL and TEM. In agreement with TEM, PL indicates a smaller and deeper potential well for the islands grown at 480°C. Concentration profiles of the WLs were measured by TEM using the CELFA method, clearly revealing segregation profiles. The segregation efficiency of In atoms obtained is 0.77 ± 0.02 (480°C) and 0.82 ± 0.02 (530°C). As an explanation for the strong mass transport of Ga from the substrate into the islands, we suggest that the segregation of In atoms during the growth of the binary InAs can lead to the generation of vacancies in the metal sublattice. The vacancies penetrate from the WL and the islands into the GaAs buffer, leading to a unidirectional diffusion of Ga atoms from the buffer into the SK layer.