Nanoindentation of hydrogenated amorphous silicon

Abstract

Nanoindentation was carried out on thin films of hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapor deposition. The composite values of elastic (Young's) modulus, E _c, and hardness, H _c, of the film/substrate system were evaluated from the load–displacement curves using the Oliver–Pharr approach. The film-only parameters were obtained employing the extrapolation of the depth profiles of E _c and H _c. Scanning probe microscopy was employed to image the nanoindenter impressions and to estimate the effect of film roughness and material pile-up on the testing results. It was established that the elastic modulus of thin a-Si:H films is in the range 117–131 GPa, which is lower than for crystalline silicon. In contrast, the values of hardness are in the range 12.2–12.7 GPa, which is comparable to crystalline silicon and higher than for hydrogen-free amorphous silicon. It is suggested that the plastic deformation of a-Si:H proceeds through plastic flow and it is the presence of hydrogen in the amorphous matrix that leads to a higher hardness.

Keywords:

• nanoindentation
• hydrogenated amorphous silicon
• elastic modulus
• hardness

Acknowledgements

The authors acknowledge using facilities in the Materials Micro-Characterization Laboratory of the Department of Mechanical Engineering and Materials Science in the Swanson School of Engineering at the University of Pittsburgh. This work was partially supported by project BK09-02 of the Institute of Solid State Physics, Bulgarian Academy of Sciences.