Phase identification from electronic structures by Auger electron spectroscopy
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A technique of phase identification from the characteristics of electronic structures is established by Auger electron spectroscopy. GaN epilayers in wurtzite and zinc-blende polytypes are used for practical investigations. Auger spectra show phase-dependent energetic shifts and peak intensity variations. Simulation of theoretical spectra reveals the substantial correlation of the Auger line shape with the bonding electronic states. This approach demonstrates the correspondence between electronic structure and atomic structure and hence provides criteria for phase identification.
I. INTRODUCTION
The characteristics of a material are dominantly attributed to its chemical composition and structural phase. A chemical molecule, for example, would probably form different crystallographic structures under appropriate conditions. Different structures will exhibit distinguishing natures in their electronic structure, atomic bonding, and even their macroscopic properties. In general, characterization techniques—such as x-ray diffraction (XRD),1 x-ray absorption fine structure (XAFS),2 transmission electron microscopy (TEM),3 etc.—have been applied to identification and determination of material structures from the atomic geometry information. In a substance, the isomers exhibit differences not only in atom-to-atom distances and orientation angles but also in the interactions within and between the bonding electrons, which is directly linked to its electronic structures. However, characterizations of different structures by the essential properties of bonding electrons remain challenging. Electron information, therefore, can be utilized as a criterion for determining the structural phases and analyzing the relative properties in detail. Auger electron spectroscopy (AES) has been proved as a powerful tools for characterization of chemical and physical properties.4–7 It is endowed with the advantages of element fingerprints, high spatial resolution (laterally 20 nm and 2–3 nm in depth), and excellent electron-state sensitivity. Theoretical interpretations of Auger spectra show that valence-band AES contains the states and correlations of valence electrons in local bonds.8–10 These advantages a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0016 J. Mater. Res., Vol. 23, No. 1, Jan 2008
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enable us to gain insights into the electron information at small scale. In this work, the technique of phase identification from electronic structures by AES is developed and applied to GaN systems. GaN epilayers in wurtzite (WZ) and zincblende (ZB) polytypes are prepared for experimental detection; meanwhile, theoretical Auger spectra of different GaN structures are simulated for thorough analysis. The connection and correspondence between electronic properties and structural phase are obtained. II. EXPERIMENTAL
GaN semiconductors have attracted wide concerns in the application of optoelectronic devices due to their outstanding character, s
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