Raman scattering from Ge nanostructures grown on Si substrates: Power and limitations

Abstract

The analysis of Raman spectra obtained for different germanium nanostructures grown on silicon substrates is presented. Comparison of these spectra with a Raman spectrum of a silicon wafer reveals a one-to-one correspondence of features located around 229, 300, and 435 cm−1. It is argued that the peaks observed at these frequencies and often ascribed to Ge nanostructures are, in fact, coming from the Si substrate. The erroneous ascription of the peaks makes the corresponding conclusions incorrect.

Epitaxial growth of silicon and germanium on (100)-oriented crystalline substrates by RF PECVD at 175 °C

“…The Raman spectra of the multilayer films deposited on GaAs and (100) Si show a sharp peak around 300 cm −1 , which is consistent with fully crystallized Ge layers [27,28]. It has been shown that a peak at 300 cm −1 could also originate from Si substrates [29], but in our case, a comparison between a Si substrate and a Si substrate capped with a thin epitaxial Ge layer showed that no signal from the Si substrate alone at 300 cm −1 was distinguishable whereas a very sharp peak would appear in the presence of this thin Ge layer. On the other hand, the film deposited on (111) c-Si substrate displays a shoulder towards lower wavenumbers, indicating that the film is partially crystallized and contains an amorphous phase, since the hydrogenated amorphous Ge has a TO mode at 278 cm −1 [28].…”

Formation of uniform high-density and small-size Ge/Si quantum dots by scanning pulsed laser annealing of pre-deposited Ge/Si film

“…The Raman spectra of all of these samples contained two distinct phonon peaks, which could be attributed to a Ge-Ge phonon mode (≈300 cm −1 ) and Si-Ge phonon mode (≈415 cm −1 ) respectively. 21 The Raman spectrum of the as-deposited sample also exhibited a broad peak at ≈270 cm −1 , which could be attributed to amorphous Ge. 22 As can be seen, the amorphous Ge peak diminished and the Ge-Ge peak got narrower with increasing number of accumulated laser shots (decreasing scan speed).…”

“…The values of I Ge-Ge /I Si-Ge for the QD samples produced at different conditions are comparable to that for self-assembled QDs grown in SK mode. 21 This means that the production of Ge/Si QDs by using SPLA does not result in a stronger intermixing than self-assembled QDs produced with SK growth, thus equally promising for applications in this respect. The Ge-Ge Raman peak should shift to the red side or the blue side when there is compressive or tensile strain in the Ge layer.…”

A hybrid model for the origin of photoluminescence from Ge nanocrystals in a SiO2matrix

“…In Ref. [20] it was argued that both features at 300 cm −1 and 430 cm −1 in such samples can be two-photon Raman peaks from the Si substrate on which the SiO 2 layer is grown. In our samples, the intensities of these peaks change with annealing, which is not expected if they arise from Si substrate (the intensity of the Si peak at 522 cm −1 remains unchanged with annealing).…”