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Open Access NANO EXPRESS

Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

Meng-Hung Lin1, Hua-Chiang Wen2*, Yeau-Ren Jeng3 and Chang-Pin Chou1

Author affiliations

1 Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan

2 Department of Materials Science and Engineering, National Chung Hsing University, Taichung, 40227, Taiwan

3 Department of Mechanical Engineering, National Chung Cheng University, Chia-Yi, 621, Taiwan

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Citation and License

Nanoscale Research Letters 2010, 5:1812-1816  doi:10.1007/s11671-010-9717-8

Published: 7 August 2010

Abstract

In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN) epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM) to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ) and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

Keywords:
Gallium nitride; Metal organic chemical vapor deposition; Nanoscratch; Atomic force microscopy