Hydrogenated Ge nanocrystals: Band gap evolution with increasing size

The electronic band structure of various Ge quantum wires of different sizes, with hydrogenated surfaces, is studied using a nearest-neighbor empirical tight-binding Hamiltonian by means of a sp(3)s* atomic orbitals basis set. We suppose that the nanostructures have the same lattice structure and the same interatomic distance as in bulk Ge and that all the dangling bonds are saturated with hydrogen atoms. These atoms are used to simulate the bonds at the surface of the wire and sweep surface states out of the fundamental gaps. One of the most important features is a clear broadening of the band gap due the quantum confinement. Comparing to experimental data, we conclude that, similar to the case of Si, the size dependent PL in the near infrared may involve a trap in the gap of the nanocrystals.