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

Sheng-Rui Jian,Jian-Ming Lu,I-Ju Teng

doi:10.1007/s11671-008-9130-8

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 (P–h) 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.

Highlights

As one of the groups III–V nitride semiconductors, GaN is a highly attractive material because of its great potential for development of optoelectronic devices in short-wave length, semiconductor lasers, and optical detectors [1, 2]
We present the Berkovich nanoindentationinduced mechanical deformation mechanisms of the metalorganic chemical-vapor deposition (MOCVD)-derived GaN thin films by means of the cathodoluminescence (CL) microscopy in a scanning electron microscopy (SEM/CL) and the cross-sectional transmission electron microscopy (XTEM) techniques
The fact that multiple ‘‘pop-in’’ events are observable over such a wide range of indentation load and penetration depth indicates the close relations to the plastic deformation of GaN thin films

Summary

Introduction

As one of the groups III–V nitride semiconductors, GaN is a highly attractive material because of its great potential for development of optoelectronic devices in short-wave length, semiconductor lasers, and optical detectors [1, 2]. The fact that multiple ‘‘pop-in’’ events are observable over such a wide range of indentation load and penetration depth indicates the close relations to the plastic deformation of GaN thin films. It cannot be provided for such indentation load any evidence of dislocation activity and crack features at the free surface around the indentation from SEM observations, as illustrated in the insert of Fig. 1.

Results

Conclusion