An investigation was made of the influence of defects emanating from P implantation damage to the InP capping layer on post-growth thermally induced intermixing in self-assembled InAs/InP(001) quantum dots. Photoluminescence spectra from as-grown samples could be described as the superposition of separate photoluminescence peaks where each peak corresponded to emission from an ensemble of quantum dots with a particular height ranging from 4 to 13ML. Blueshifts of up to 270meV and significant bandwidth broadening were observed in the photoluminescence spectra after ion implantation to a fluence of 5 x 1011 to 1014/cm2 and subsequent annealing at 450 to 600C. From an analysis of the evolution of the quantum dot peaks upon intermixing, which revealed the coexistence of intact quantum dot photoluminescence and a broad photoluminescence feature related to heavily intermixed quantum dots, it was suggested that the bandwidth broadening resulted from spatial inhomogeneity in the compositional intermixing. In order to understand better the mechanism responsible for the ion-implantation-induced intermixing, samples capped with a stack of compressively strained In0.75Ga0.25As/InP quantum wells were prepared to trap vacancies released by the implantation damage while not inhibiting the effect of the interstitials. Both blueshift and bandwidth broadening were suppressed in samples containing the strained InGaAs quantum wells, whereas the evolution of the photoluminescence spectra from the quantum dots behaved as expected for interstitial-mediated intermixing. The vacancies were thus believed to be trapped in the quantum wells and indicated that intermixing in ion-implanted InP capped samples was mediated by vacancies. The shape of the quantum dots changed from a truncated pyramid in the as-grown state to a double convex lens structure after intermixing as confirmed by cross-sectional scanning transmission electron microscopy imaging. Furthermore, the change in shape and compositional intermixing of the quantum dots were attributed to vacancy trapping in the vicinity of the quantum dots, as based upon atomistic strain calculations.

Vacancy-Mediated Intermixing in InAs/InP(001) Quantum Dots Subjected to Ion Implantation. C.Dion, P.Desjardins, F.Schiettekatte, M.Chicoine, M.D.Robertson, N.Shtinkov, P.J.Poole, X.Wu, S.Raymond: Journal of Applied Physics, 2008, 104[4], 043527