Electron accumulation in small and larger semiconductor quantum dots

We present μ-PL and k·p calculations of self-assembled InP quantum dots (QDs) in GaInP. The QDs come in two subsets; the larger are pyramid shaped, and about 15 nm high with a base of about 40 by 50 nm, and the smaller have similar lateral extension but with a considerably lesser height. The change in size is accompanied by a change in quantum confinement and thus a change in emission energy. Moreover, there is a transition from a single sharp emission peak for the smallest dots to several 1 meV broad lines over a 50 meV range for the largest dots due to unintentional doping in the barrier material. The result is an electron accumulation in the QDs, and emission in an energy range corresponding to the energy range occupied by these electrons. Larger QDs accumulate more electrons and thus emit over a larger energy range. For the smaller dots we show that the precise position of the electronic ground state with respect to the Fermi level determines whether the dot is neutral or charged