Raman scattering from fully strained Ge1−xSnx (x⩽0.22) alloys grown on Ge(001)2×1 by low-temperature molecular beam epitaxy

Abstract

Fully strained single-crystal Ge1−xSnx alloys (x⩽0.22) deposited on Ge(001)2×1 by low-temperature molecular beam epitaxy have been studied by Raman scattering. The results are characterized by a Ge–Ge longitudinal optical (LO) phonon line, which shifts to lower frequencies with increasing x. Samples capped with a 200-Å-thick Ge layer exhibit a second Ge–Ge LO phonon line whose position remains close to that expected from bulk Ge. For all samples, capped and uncapped, the frequency shift ΔωGeSn of the Ge–Ge LO phonon line from the Ge1−xSnx layer, with respect to the position for bulk Ge, is linear with the Sn fraction x (ΔωGeSn=−76.8x cm−1) over the entire composition range. Using the elastic constants, the Grüneisen parameter, and the shear phonon deformation parameter for Ge, we calculate the contribution of compressive strain to the total frequency shift to be Δωstrain=63.8x cm−1. Thus, the LO phonon shift in Ge1−xSnx due to substitutional-Sn-induced bond stretching in fully relaxed alloys is estimated to be Δωbond =−140.6x cm−1.

Laser CVD of Nanodisperse Ge–Sn Alloys Obtained by Dielectric Breakdown of SnH4/GeH4 Mixtures

“…The Raman spectrum of the deposit ( Figure 3) shows a broad band at 282-288 cm -1 and a sharp band at 518-520 cm -1 with a shoulder at 490 cm -1 , which are, respectively, assigned to the Ge-Ge bond in a Sn/Ge alloy, [11] the Si-Si bond in the silicon substrate and the Si-Si bond in Si/ M (M = Sn, [27] Ge [28] ) alloys. The Ge-Ge band being shifted from that of pure Ge (ca.…”

“…The Ge-Ge band being shifted from that of pure Ge (ca. 300 cm -1 ) corresponds [11] to the Sn Both vibrational spectra do not indicate the presence of interstitial hydrogen. [Although this species has not yet been detected for Sn and Ge/Sn, it is infrared active in Ge at 700 and 1880 cm -1 (ref.…”

“…Up to now, coevaporation of Sn and Ge and deposition to substrates kept at 100 K allowed [6] formation of amorphous single phase (x Յ 0.15) films, sputtering resulted in deposition of amorphous [7] and single-crystal or polycrystalline films (x Յ 0.15), [8] molecular beam epitaxy (MBE) enabled the growth of homogeneous crystalline (x = 0.2-0.5) [9][10][11] and fully strained (x Յ 0.26) [12] films on Ge, InSb [13] (x Յ 0.1) and CdTe [14] substrates, ion-assisted MBE yielded [15] crystalline d-c films (x = 0.3-0.34) on Ge, ultrahigh-vacuum chemical vapour deposition from Ge 2 H 6 and SnD 4 precursors allowed synthesis of crystalline strainfree films (x Յ 0.20) on silicon substrates [16][17][18] and, finally, pulsed laser annealing of amorphous Ge/Sn films resulted in the formation of metastable crystalline features with x = 0.22 on glass [5] and even x = 0.55 on Ge [19] substrates. Another laser technique enabling kinetic rather than thermodynamic control of the process is IR laser-induced gas-phase codecomposition of two different molecules, [20,21] which is capable of simultaneously generating clusters of several (two or more different) metals that will interact in the gas phase to yield "mixed nanosized systems" and deposit as such from the gas phase.…”

Ion-beam synthesis and thermal stability of highly tin-concentrated germanium – tin alloys

“…According to Ref. 19 , for a fully strained Ge-Sn alloy, the shift equation can be simplified to ∆ − = 76.8 × ∁ .…”

Simple chemical routes to diamond-cubic germanium–tin alloys

“…Thin films were deposited on oxidized and oxide-free Si by reactions of (Ph͒SnD 3 with Ge 2 H 6 at 350°C. [6][7][8][9] The chemical vapor deposition ͑CVD͒ sources that are normally used in synthesis of Si-based semiconductors are the hydrides SiH 4 , GeH 4 , Si 2 H 6 , Ge 2 H 6 and their chlorinated derivatives. As-deposited Ge 1Ϫx Sn x on oxidized Si displayed good crystallinity which improved significantly by annealing at 400°C.…”