Optical bandgap energy of Si nanoparticle composite films deposited by a multi-hollow discharge plasma chemical vapor deposition method

Semiconductor nanoparticles have significant potential for optoelectronic applications such as solar cells and light-emitting diodes. We are developing semiconductor nanoparticle composite films with a wide bandgap to be used as the window layer of solar cells because the bandgap energy increases with a decrease in the size of particles in the nanometer size range due to the quantum size effect. A multi-hollow discharge plasma chemical vapor deposition (CVD) method was used to fabricate Si nanoparticle composite films and control the volume fraction of nanoparticles in the films. The bandgap energy was increased from 2 eV for a crystalline volume fraction X_c of 0.2 to 2.5 eV for X_c = 0.6 and then decreased to 1.1 eV for X_c = 1. The photo and dark conductivity of films indicate high stability against light soaking. Si nanoparticle composite films with bandgap energies above 2.2 eV are thus promising candidate materials for the window layer of thin-film solar cells.