LOCALIZATION OF ELECTRONS IN WIRE-LIKE POROUS SILICON

We investigate the possible localisation of electrons in wire-like por ous Si (H-passivated Si), which can come from the undulation of the wi re diameter from 20 to 40 Angstrom over a length of 40 Angstrom. We us e the Effective Mass Theory (EMT) and to simulate the ''bumpy'' wire w e employ a supercell composed of concentric cylinders with random diam eters and periodic boundary conditions at its ends. We find that the l ow-lying states are localised inside particular cylinders of the super cell whereas further up - typically a few tenths of eV higher - one fi nds states extending through the whole of the wire. Our results suppor t the model of luminescence from bulk states irrespective of the chara cter of the band gap and can explain the constancy of the mobility wit h temperature and also the smooth transition of the luminescence spect rum from wire-like to dot-like structures.