Hydrogen-mediated structural changes of amorphous and microcrystalline silicon

Amorphous $(a-\mathrm{S}\mathrm{i}:\mathrm{H})$ and microcrystalline silicon $(\mu c-\mathrm{S}\mathrm{i}:\mathrm{H})$ samples were exposed to a hydrogen plasma in a clean electron-cyclotron-resonance system. We present unequivocal experimental evidence for hydrogen-induced crystallization of $a-\mathrm{S}\mathrm{i}:\mathrm{H}.\mathrm{}$ A 60-min post-hydrogenation at 325 °C resulted in an increase of the crystalline fraction by 10–15 %. Similar H plasma treatments performed on $\mu c-\mathrm{S}\mathrm{i}:\mathrm{H}$ 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.