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Open Access Nano Express

Cathodoluminescence and Cross-sectional Transmission Electron Microscopy Studies for Deformation Behaviors of GaN Thin Films Under Berkovich Nanoindentation

Sheng-Rui Jian1*, I-Ju Teng2 and Jian-Ming Lu3

Author Affiliations

1 Department of Materials Science and Engineering, I-Shou University, Kaohsiung, 840, Taiwan

2 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan

3 National Center for High-Performance Computing, National Applied Research Laboratories, No. 28, Nanke 3rd Rd., Sinshih Township, Tainan County, 74147, Taiwan

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Nanoscale Research Letters 2008, 3:158-163  doi:10.1007/s11671-008-9130-8

Published: 15 April 2008

Abstract

In this study, details of Berkovich nanoindentation-induced mechanical deformation mechanisms of metal-organic chemical-vapor deposition-derived GaN thin films have been systematic investigated with the aid of the cathodoluminescence (CL) and the cross-sectional transmission electron microscopy (XTEM) techniques. The multiple “pop-in” events were observed in the load-displacement (Ph) curve and appeared to occur randomly by increasing the indentation load. These instabilities are attributed to the dislocation nucleation and propagation. The CL images of nanoindentation show very well-defined rosette structures with the hexagonal system and, clearly display the distribution of deformation-induced extended defects/dislocations which affect CL emission. By using focused ion beam milling to accurately position the cross-section of an indented area, XTEM results demonstrate that the major plastic deformation is taking place through the propagation of dislocations. The present observations are in support to the massive dislocations activities occurring underneath the indenter during the loading cycle. No evidence of either phase transformation or formation of micro-cracking was observed by means of scanning electron microscopy and XTEM observations. We also discuss how these features correlate with Berkovich nanoindentation produced defects/dislocations structures.

Keywords:
GaN; MOCVD; Nanoindentation; Cathodoluminescence; Focused ion beam; Transmission electron microscopy