Analysis of size distributions of type IIZnTe/ZnSe quantum dots

Abstract

The photoluminescence (PL) spectrum of the ZnTe/ZnSe quantum dot (QD) structure which has a type II band alignment. was investigated. A broader structure peaking at 2.180 eV together with the features of the ZnSe buffer layer located at 2.820 eV in the PL spectrum at 10 K were observed. The broadness of the PL attributes to the spatial inhomogeneity of the QD sizes. The PL spectrum was a normal distribution with a variance of 0.002 eV(2). However, the dot size distribution was a deformed Gaussian. Using only one set of data of dot size distribution measured by the Atomic Force Microscopy (AFM), the statistical estimates with standard errors were evaluated using the bootstrap methodology. The probability distribution was inferred by calculating the means, percentiles and correlation coefficients of the base diameter and the height of the QDs. We concluded that the dot distributions were indeed a deformed Gaussian and the correlation coefficient of the diameter and the height of the QDs was 0.49 +/- 0.01. The uniformity of the dot size distribution was poor. To infer the dot size distribution from the PL spectrum, we numerically solved the Schrodinger equation by elaborating on the orthogonal periodic functions (OPF) approximation for the type II lens shaped QDs. The convergence of the probability density was discussed in a great detail. We found that the band edge discontinuities inside the dot acts as a barrier with DeltaE(v) = 315 meV for the conduction band and as a well with DeltaE(v) = 735 meV for the valence band. In the AFM measurement, the offset in dot height is 14 Angstrom and the aspect ratio is 0.04. We employed the Schrodinger equation to correlated the PL spectrum (intensity versus optical energy) to the AFM data (number of QDs versus dot size) and the agreement was excellent. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.