Raman Spectroscopy
Deals with lattice vibrations studied by Raman spectroscopy. First, a description of the fundamentals of this technique is provided. Special emphasis is paid to a detailed description of the main experimental issues, e.g. spectrometers, detectors, optics,
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Raman Spectroscopy
Abstract Deals with lattice vibrations studied by Raman spectroscopy. First, a description of the fundamentals of this technique is provided. Special emphasis is paid to a detailed description of the main experimental issues, e.g. spectrometers, detectors, optics, and how to use them. A detailed analysis of the “information depth” and lateral resolution is given. A discussion of the alternatives to improve the resolution is presented, in particular, the confocality, and tip enhanced methods are introduced. Several case applications highlighting the capabilities of the technique are presented; in particular, the measurement of stresses in silicon based devices, the coupled phonon-plasmon modes that allow to study in a contact-less way the transport parameters at a submicron scale; the use of the micro-Raman spectroscopy as local temperature probe, or the influence of the low dimensionality in the Raman spectrum are presented.
3.1
Introduction
Raman spectroscopy is widely used as an optical characterization tool for investigating semiconductors in bulk, thin film, nanostructured, and device forms [1–10]. When light interacts with a solid, several phenomena take place, e.g. reflection, absorption, and light scattering. The light scattering can be either elastic (Rayleigh), or inelastic (Chap. 1). The Raman effect is an inelastic scattering phenomenon in which elementary excitation energy quanta of the solid are exchanged with the excitation electromagnetic wave. In Raman spectroscopy, those elementary excitations are optical phonons. Because lattice vibrations are very sensitive to the local structure and lattice environment, the Raman spectrum supplies information about the physical factors that disturb the local order or modify the interatomic distances. A great number of fundamental properties of semiconductors can be studied by Raman spectroscopy, i.e., crystal orientation, lattice temperature, symmetry breakdown, strain, chemical composition, among others; moreover, electronic and thermal properties can also be probed. This information is crucial to build up a diagnosis about the properties of the semiconductors as basic materials, as well as the changes © Springer International Publishing Switzerland 2016 J. Jimenez and J.W. Tomm, Spectroscopic Analysis of Optoelectronic Semiconductors, Springer Series in Optical Sciences 202, DOI 10.1007/978-3-319-42349-4_3
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3 Raman Spectroscopy
induced after the different processing steps undergone by the semiconductor during the device fabrication. In fact, all the physical factors mentioned above affect fundamental properties of the semiconductors, with the concomitant consequences on the device performance and reliability. Strain and temperature are important reliability issues in electronic devices. In fact, many problems concerning failed devices can be linked to the defects generated by stresses during the device processing [11], or the thermal stresses generated during the device operation [12, 13]. On the other hand, the increasing impor
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