Experimental investigations into the formation of nanoparticles in a∕nc-Si:H thin films

Abstract

Hydrogenated amorphous silicon thin films with nanocrystalline silicon inclusions (a∕nc-Si:H) have received considerable attention due to reports of electronic properties comparable to hydrogenated amorphous silicon (a-Si:H) coupled with an improved resistance to the light-induced formation of defects. In this study, a∕nc-Si:H thin films are synthesized via radio-frequency plasma-enhanced chemical-vapor deposition with helium and hydrogen diluted silane. The plasma conditions were chosen to simultaneously deposit both Si nanocrystallites and an amorphous silicon matrix. This structure has been confirmed by transmission electron microscopy (TEM) studies. Both plasma electronic diagnostics and TEM image analysis of a∕nc-Si:H films deposited with and without a temperature gradient between the capacitively coupled reactor electrodes suggest nanoparticle formation in the plasma, as opposed to solid-state nucleation of the nanoparticles in the film. Optical-absorption studies of the a∕nc-Si:H films indicate electrical properties comparable to a-Si:H. In particular, the evolution of the films’ photoconductivity over light exposure time shows a Staebler–Wronski effect similar to a-Si:H.