Influence of alloy inhomogeneities on the determination by Raman scattering of composition and strain in Si1–xGex/Si(001) layers

Abstract

Monitoring the in-situ oxide growth on uranium by ultraviolet-visible reflectance spectroscopy J. Appl. Phys. 112, 093104 (2012) Experimental investigation of photonic band gap influence on enhancement of Raman-scattering in metaldielectric colloidal crystals J. Appl. Phys. 112, 084303 (2012) Design of lumpy metallic nanoparticles for broadband and wide-angle light scattering Appl. Phys. Lett. 101, 141112 (2012) Experimental surface-enhanced Raman scattering response of two-dimensional finite arrays of gold nanopatches Appl. Phys. Lett. 101, 111606 (2012) Origins of high visible light transparency and solar heat-shielding performance in LaB6 Appl. Phys. Lett. 101, 041913 (2012) Additional information on J. Appl. Phys. In this work, we investigate the influence of alloy composition inhomogeneities on the vibrational properties of strained Si 1Àx Ge x /Si layers with x ranging from 0 to 0.5. We show that the frequencies of the principal alloy vibrational modes (Ge-Ge, Si-Ge, and Si-Si) are strongly influenced by the distribution of Ge atoms within the alloy layers, which becomes gradually random following a series of sequential annealing steps. Our measurements suggest that the composition dependence of the optical phonon frequencies in fully random and unstrained alloys is well described by the results previously published by Alonso and Winer [Phys. Rev. B 39, 10056 (1989)]. In the general case of an alloy layer with unknown degree of compositional inhomogeneity and/or strain relaxation, though the analysis of the Raman spectra is not straightforward. Therefore, we propose an analytical/graphical method to accurately estimate the Ge content and residual strain of SiGe layers exhibiting any level of compositional disorder or strain status, by performing a single Raman measurement. This would be extremely useful in situations where x-ray measurements cannot be conducted. We show that our procedure to treat the Raman data holds for the whole compositional range but with different accuracy depending upon the case: (i) For annealed SiGe layers (mostly strain relaxed) the Ge content x can be directly determined with high accuracy of 60:01. (ii) For strained samples (usually as-grown samples) an extra criterion must be adopted seeking for a graphical solution, accounting for the degree of compositional inhomogeneity. In this case, the error in the determination of Ge content depends on alloy composition, being the upper bound 60:02 for x < 0:3 and 60:03 for x > 0:3. V C 2012 American Institute of Physics. [http://dx

Germanium-silicon alloy and core–shell nanocrystals by gas phase synthesis

“…By determining the position of the strong first order lines resulting from the nearest neighbor atomic vibrations of Ge-Ge, Ge-Si and Si-Si Raman analysis allows for the determination of x Ge (see Materials and methods section) according to Reparaz et al, 25 Tsang et al 26 and Alonso and Winer. 27 In Fig.…”

“…The peak position ω of either the Si-Si or the Ge-Ge peak is used to evaluate the actual composition x Ge following eqn (1) and (2) respectively. 25 The prominent peak of each spectrum is used for this determination, i.e. the Ge-Ge peak for 0.9 ≤ x Ge ≤ 0.6 and Si-Si peak for 0.5 ≤ x Ge ≤ 0.1.…”

Review—Towards the Next Generation of Thermoelectric Materials: Tailoring Electronic and Phononic Properties of Nanomaterials

“…To test this thermal rectification effect, multilayered samples of graded SiGe sequences were fabricated via MBE on silicon substrates. Different studies on the influence of alloy inhomogeneities on the composition or strain of these layers, 38 showed that the transport properties of such structures could be tailored, obtaining thermal conductivity values as low as 2.2 W · m −1 · K −1 .…”

Characterization of Hetero-Epitaxial Ge Films on Si Using Multiwavelength Micro-Raman Spectroscopy

“…The peak position shifts under the presence of strain/stress and isotopic variations. 4,5,9,[27][28][29][30][31] Alloys of Si and Ge (Si 1-x Ge x ) typically show three Raman peaks of Ge-Ge (∼300 cm −1 ), Si-Ge (∼400 cm −1 ) and Si-Si (∼500 cm −1 ). The position and intensity of the three peaks depends on the composition of the alloys.…”

“…27,28 For precise analysis, more careful interpretation is needed. Perhaps, additional information from XRD, SIMS, X-SEM and X-TEM results will be very useful, in early stages, for verification of Raman characterization results.…”