Infrared Absorption of Lattice Modes and the Silicon Local Mode in GexSi1−x Alloys

Abstract

Measurements have been made of the infrared absorption of GexSi1−x alloys for x≤0.12 and x≥0.88. The measurements were made in the range 100–700 cm−1 at temperatures from 10 to 300°K. In Si-rich alloys (x≤0.12) absorption bands are seen near 485, 400, and 125 cm−1 which are essentially temperature independent, indicating a single-phonon process. The bands do not correspond well with the predictions of simple models for resonance mode absorption, but are more nearly characteristic of the single-phonon density of states for Si. In the Ge-rich alloys (x≥0.88) the Si localized mode is observed as an absorption band at 389 cm−1 for x=0.99, increasing to 394 cm−1 at x=0.88. The absorption cross section αpeak/[Si] is only 4×10−21 cm2, smaller by 102−103 than observations for other local modes in semiconductors. Two-phonon absorption bands at about 200 and 290 cm−1 in Ge are enhanced by the addition of Si. The over-all temperature dependence of the absorption strength is large enough that it is not obvious whether the observed enhancement is temperature dependent or is a temperature-independent absorption, caused by the Si, superposed on a temperature-dependent background.

Phonons inGe1−xSixbulk crystals

“…Several papers have been published investigating the lattice dynamics of bulk Ge 1Ϫx Si x crystals by infrared ͑IR͒ absorption, [1][2][3][4] Raman, [5][6][7][8][9] and theory. 10,11 Despite these previous investigations, phonon spectra of Ge 1Ϫx Si x crystals still show several discrepancies.…”

“…Ge-Si vibrations in the alloy have been previously investigated by IR absorption [2][3][4] and Raman 5-8 measurements.…”

Thermal donors in silicon-rich SiGe

“…and Si samples is a band at 485 cm Ϫ1 ͑IB͒. 8,9 This band was attributed to a TO mode becoming IR active by the perturbation caused by Ge atoms. 8 As shown in Fig.…”

Vibrational Modes in SixGe1-xAlloys: Temperature and Compositional Dependence

“…They represent a continuous series of crystalline materials with gradually varying properties. Vibrational states of the SiGe 1 -x alloys have been studied several times by infrared methods [1][2][3].In this paper, we present infrared absorption spectra of bulk Si x Ge1-x alloy for 0 < x < 1 in the spectral range 375-1200 cm -1 . As far as we know, it is for the first time that the local vibrations of the interstitial oxygen in the alloys are reported.…”

“…They represent a continuous series of crystalline materials with gradually varying properties. Vibrational states of the SiGe 1 -x alloys have been studied several times by infrared methods [1][2][3].…”