The unique versatility of micro-Raman spectroscopy (μRS) in semicon- ductor physics remains in Raman imaging. Numerous applications cover the whole development of modern electronic and optoelectronic devices: from semiconduc- tor growth to advanced device inspection tools. In this chapter, a wide variety of semiconductors (SiC, graphene, GaN, GaAs, SiGe, strained Si, sSOI, SGOI) and devices (FETs, lasers, MEMS) are addressed. First, it will be shown how Raman mapping enables to check the crystalline quality, the composition, the doping, and the uniformity of as-grown semiconductors. Then, we will focus on the most popular application in microelectronics: strain measurements either at the device or at the full wafer scale. Finally, we will show how μRS imaging can be used for final device inspection through the temperature mapping of operating devices (FETs, lasers, actuators).

The Raman bands intensities, frequencies, widths and profiles of few layer graphene (FLG) are extremely sensitive to doping, strain, stacking order, number of graphene sheets, crystalline quality and laser wavelength. For samples of epitaxial graphene grown on silicon carbide, the laser wavelength is basically the only factor known a priori. Furthermore, the concomitance of second order SiC Raman modes in the graphene G and D bands region complicates the extraction of the graphene signal. Developing a robust characterization tool enabling to disentangle all these effects and to provide reliable information is thus highly needed and challenging. We propose an approach where micro-Raman spectroscopy is combined with reflectivity and transmission measurements to discriminate between the different contributions in the measured Raman signatures and to access to the detailed characteristics of the samples. Here, we demonstrate the efficiency of this method in order to determine the number of graphene layers. We address then the question of using the 2D band width or ratio of the 2D and G bands intensities as a criteria to distinguish between mono and multi layer(s) graphene.

A detailed comparison of true epitaxial graphene monolayers grown on both faces of 6H SiC substrates (Si and C faces) is made by combining micro-Raman spectroscopy with transmission measurements. We have already shown that such combination allows to discriminate without any ambiguity between a graphene monolayer and a twisted or folded graphene bilayer (AA') grown on the C face of 6H SiC [1]. In this presentation, we will focus on the Raman spectra and the transmission measurements performed on graphene monolayers grown on the Si face of 6H SiC. The graphene growth was tuned to get a mixed surface at the early stage of graphitization with i) bare SiC, ii) buffer layer and iii) in some localized areas small monolayers flakes on top of the buffer layer. These unique samples enabled to measure properly the Raman spectrum of the buffer layer (carbon layer with a large number of sp3 bonds) and its optical extinction at 514.5 nm. The Raman spectrum of this buffer layer remains visible after the growth of one monolayer on top but the Raman intensity is strongly reduced (typically divided by a factor of 3). This cannot be attributed to the absorption coefficient of graphene which is relatively low (few percents). Finally, several Raman mapping reveal the uniformity of the graphene monolayers in terms of thickness and crystalline quality, but also that they are subjected to a non uniform compressive strain.

The present work is proposing a comparative analysis of the graphitization, achieved by argon-propane assisted chemical vapor deposition, of 6H-SiC(0001) bulk substrates and 3C-SiC heteroepilayers deposited on (111) and (100) silicon. We have investigated the influence of the experimental parameters of the graphitization (pressure, propane flow rate and duration) both on the structural and the electrical properties of the graphitic/graphene phases developed at the samples surface. In particular, the growth mode has been highlighted. It has been shown that, in our experimental conditions, the formation of graphene is only a transitory step followed by a stage of rapid over-deposition of the surface by a highly disordered graphitic phase. This can be understood by a surface chemical potential variation accompanied by a balance between some mass transport at the surface (which could include sublimation) and a deposition regime. It shows that the process time must be properly adjusted to conserve the graphene at the surface. Furthermore, it is shown that the graphene sheet resistance is significantly dependent on the surface uniformity and can be tuned by varying the process pressure.

Graphite Intercalation Compounds have been the subject of intensive research. With the rise of graphene, new opportunities emerge in the field. On the one hand, adsorption and/or intercalation of hetero-atoms offer a gateway to tune graphene properties. On the other hand, investigations on a simpler system open the way towards increasing knowledge on the intercalant/host physical properties. New questions to be addressed also arise, such as, what happens when the number of layers is reduced? We have developed a setup derived from the two zone vapor transport method used to produce graphite intercalation compounds. It allows performing in situ Raman experiments during graphene doping by alkali vapor. The results obtained on the evolutions of the G and 2D bands during rubidium doping of graphene and bilayer graphene will be presented and discussed.

Raman results obtained on graphene edges will be presented. In a first study, the variation of the relative intensity of the D and G band as a function of the graphene ribbon width was investigated. In a second one, we developed an hyperspectral Raman method in order to determine the evolution of the ID/IG ratio as a function of excitation wavelength. Our results will be discussed in regards with published data on graphite nanocristallites and more recently on graphene.

In this article, a multiscale investigation of few graphene layers grown on 6H-SiC(000-1) under ultrahigh vacuum (UHV) conditions is presented. At 100-mu m scale, the authors show that the UHV growth yields few layer graphene (FLG) with an average thickness given by Auger spectroscopy between 1 and 2 graphene planes. At the same scale, electron diffraction reveals a significant rotational disorder between the first graphene layer and the SiC surface, although well-defined preferred orientations exist. This is confirmed at the nanometer scale by scanning tunneling microscopy (STM). Finally, STM (at the nm scale) and Raman spectroscopy (at the mu m scale) show that the FLG stacking is turbostratic, and that the domain size of the crystallites ranges from 10 to 100 nm. The most striking result is that the FLGs experience a strong compressive stress that is seldom observed for graphene grown on the C face of SiC substrates.