Decoupling the effects of composition and strain on the vibrational modes of GeSn semiconductors

Abstract

We report on the behavior of Ge-Ge, Ge-Sn, Sn-Sn like and disorder-activated vibrational modes in GeSn semiconductors investigated using Raman scattering spectroscopy. By using an excitation wavelength close to E1 gap, all modes are clearly resolved and their evolution as a function of strain and Sn content is established. In order to decouple the individual contribution of content and strain, the analysis was conducted on series of pseudomorphic and relaxed epitaxial layers with a Sn content in the 5-17at.% range. All vibrational modes display qualitatively the same behavior as a function of content and strain, viz. a linear downshift as the Sn content increases or the compressive strain relaxes. Simultaneously, Ge-Sn and Ge-Ge peaks broaden, and the latter becomes increasingly asymmetric. This asymmetry, coupled with the peak position, is exploited to implement an empirical approach to accurately quantify the Sn composition and lattice strain from Raman spectra.Understanding the behavior of different vibrational modes in a semiconductor is of paramount importance to probe its crystal phase and symmetry, composition, lattice strain, isotopic content, electronic and phononic properties. [1][2][3] In this regard, Raman scattering spectroscopy has thus become an ubiquitous characterisation technique as information-rich spectra are acquired from straightforward and non-destructive measurements. Therefore, it is commonly used to evaluate the chemical composition and lattice properties of, for instance, group-IV semiconductors such as strained Si, 4-6 strained Ge, 7-10 SiGe, [11][12][13][14] and GeSn layers. [15][16][17][18][19][20][21][22][23][24][25] The latter are particularly of growing interest because of their relevance to Si-compatible light emission and detection applications in the short-and mid-wavelength infrared, [26][27][28][29][30][31][32][33][34][35] which can lead to the integration of optoelectronic and photonic circuits on complementary metal-oxide-semiconductor (CMOS) platforms. [36][37][38] Previous reports on the vibrational modes of GeSn mainly focused on Ge-Ge longitudinal optical (LO) mode as the analyses relied on the use of 488 nm 15,16 or 532 nm 18-24 excitation lines. Under these conditions, the signal-to-noise ratio is too low to clearly distinguish Sn-related vibrational modes in the vicinity of the more prominent Ge-Ge LO peak. This also applies to the study of ternary SiGeSn semiconductors. [39][40][41] When using a 633 nm excitation laser, the signal-tonoise ratio is significantly enhanced, thus allowing a clear distinction of Ge-Ge and Ge-Sn modes, in addition to other features such as disorder-activated (DA) and Sn-Sn like modes. This higher sensitivity is attributed to the increase in Raman scattering cross section when the excitation wavelength becomes close to the material's E1 gap. 39,42 Oehme et al. 25 and D'Costa et al. 17 provided a quantitative description of the evolution of peak positions as a function of the composition. However, in these studies, the investigated sampl...

Midinfrared Emission and Absorption in Strained and Relaxed Direct-Band-Gap Ge1−xSnx Semiconductors

“…The layers investigated in this work are grown on 4-in. Si (100) wafers in a low-pressure chemical vapor deposition (CVD) reactor using ultrapure H 2 carrier gas, and 10% monogermane (GeH 4 ) and tin-tetrachloride (SnCl 4 ) precursors, following a recently developed growth protocol [4,7,18,19]. First, a 600-700 nm-thick Ge-VS is grown at 450°C, followed by thermal cyclic annealing (>800°C) and additional Ge deposition.…”

“…First, a 600-700 nm-thick Ge-VS is grown at 450°C, followed by thermal cyclic annealing (>800°C) and additional Ge deposition. The Ge 0.83 Sn 0.17 sample with a uniform composition is grown using a Ge 1-x Sn x multilayer heterostructure, where the incorporation of Sn is controlled by the growth temperature [18]. The 17 at.…”

All‐Group IV Transferable Membrane Mid‐Infrared Photodetectors

“…The growth of GeSn multilayers was then performed at temperature below 350 °C for a variable growth time. The composition of each layer was controlled by the growth temperature, [ 64 ] while the Ge/Sn ratio in gas phase was kept constant or slightly increased with decreasing temperature to prevent phase separation during growth. In the Ge 0.895 Sn 0.105 sample the multilayers were grown at 340 °C (#1), 330 °C (#2), 320 °C (#3), and 310 °C (TL), while in Ge 0.87 Sn 0.13 an additional layer was grown at 300 °C (TL).…”

“…In the Ge 0.83 Sn 0.17 sample growth temperatures of 320 °C (#1), 300 °C (#2), and 280 °C (TL) were used. [ 35,45,64 ]…”

“…In the Ge 0.83 Sn 0.17 sample growth temperatures of 320 °C (#1), 300 °C (#2), and 280 °C (TL) were used. [35,45,64] Raman Measurements: Raman measurement was performed using an InVia Raman microscope with a 633 nm laser and equipped with a 1800/ mm diffraction grating. Note that in Raman spectra the contribution from the lower Sn content layers (#1-2) is negligible because of the penetration depth of the 633 nm excitation laser being limited to less than 30 nm, thus significantly smaller than the 17 at% TL thickness of 160 nm.…”