DF-HF COMPUTATION OF Si QDs: INTRINSIC STRESS, ISO-VALENT IMPURITIES AND VALIDITY OF THE EFFECTIVE MASS APPROXIMATION (talk)

We report on ab-initio Density-Functional { Hartree-Fock (DF-HF) computations of hydrogen (H) - terminated Si approximants with a diameter of dQD = 3.4 to 18.3 Å. A structual optimization of these Si quantum dots (QDs) shows their effort to form a possibly spherical shape, which induces stress on the adjacent dielectric matrix due to an intrinsic distortion of Si atoms at the QD surface. With the optical band gap of the Si QDs obtained from DF-HF computations we evaluate the effective mass approximation (EMA) by calculating the ground state in a fnite potential sphere comprising the volume of the respective Si QD. We show that the EMA becomes increasingly invalid for dQD <= 30 Å for Si. Computing Si QDs with and without an iso-valent impurity being exchanged for the central Si atom we evaluate the consequences for their electronic structure. While still being a model case, monatomic iso-valent doping shows to be a candidate for an improved energy selective contact (ESC).
Keywords: Quantum Dots { 1: Modelling { 2: Fundamentals { 3