Energy levels in metal oxide semiconductor quantum dots in water-based colloids

The three-dimensional Schrodinger and Poisson's equations are used to calcu late the conduction band profile, energy levels, and Fermi energy of negati vely charged semiconductor quantum dots. The calculation is carried out sel f-consistently within the frame of the finite-difference method. Assuming t he effective mass of the proton at the semiconductor-electrolyte interface, we found the conduction band profile for the spherical ZnO quantum dots di spersed as aqueous colloids very similar to the conduction band profile of symmetric modulation-doped semiconductor quantum wells. The energy levels a nd Fermi energy of the spherical ZnO quantum dots are obtained as a functio n of the band offset at the semiconductor-electrolyte interface. A comparis on of the energy levels for negatively charged and uncharged quantum dots i s used as an alternative explanation of the observed reversible blue shift in the absorption spectrum of semiconductor colloids under illumination. (C ) 1999 American Institute of Physics. [S0021-9606(99)70142-X].