Hydrogen-mediated structural changes of amorphous and microcrystalline silicon

Amorphous (a-Si:H) and microcrystalline silicon (mu c-Si:H) samples were exposed to a hydrogen plasma in a clean electron-cyclotron-resonance system. We present unequivocal experimental evidence for hydrogen-induced crystallization of a-Si:H. A 60-min post-hydrogenation at 325 degrees C resulted in an increase of the crystalline fraction by 10-15 %. Similar H plasma treatments performed on mu c-Si:H caused a decrease of the crystalline fraction X-C by up to 20%. The lack of an amorphous phase in posthydrogenated c-Si shows that the presence of grain boundaries is required to observe hydrogen-induced conversion of crystalline to amorphous silicon. We propose that the driving force for the decrease of X-C is the minimization of the lattice-strain energy.