Calculations of electronic and optical properties of diamond quantum films

Energy gaps and oscillator strengths (lifetimes) for (0 0 1) ultrathin quantum films of diamond are calculated by the extended Hückel-type nonorthogonal tight-binding method. For the diamond films with monohydrogenated dimers on the surface, a lowest unoccupied surface state (LUSS) occurs just below the conduction-band minimum of the diamond bulk at the center of the (0 0 1) surface Brillouin zone, and that a direct energy gap is formed between the LUSS and the film valence-band maximum. Calculations of the density of states show that the LUSS extends into the deeper C layers up to the ninth layer, and that a significant s-orbital character is incorporated into the LUSS by the formation of the monohydrogenated dimer on the film surface, which is responsible for significant oscillator strength for optical transitions across the energy gap. It is shown that calculated lifetimes across the energy gap are less than 100 μs, suggesting that the quantum films of diamond studied have potential as light-emitting materials.