Calculations of electronic states in ultrasmall quantum boxes of diamond

Abstract

The electronic structure of ultrasmall quantum boxes (QBs) of diamond with (110), (11¯0), and (001) planes saturated by hydrogen is calculated using the extended Hückel-type nonorthogonal tight-binding method. It is shown that in contrast to the QBs with the ideal surfaces, which show a clear dependence of the lowest unoccupied molecular orbital (LUMO) energy on the size variation along the [001] direction, the energy of the LUMO state in the QBs with a monohydrogenated dimer on the (001) surface depends little on the size variation in agreement with the experiment. It is found that the LUMO state in the latter is surfacelike in character and associated with backbonds of the surface dimers. It is also demonstrated that optical transitions across the energy gap exhibit significant oscillator strength.