Composition-Dependent Phonon and Thermodynamic Characteristics of C-Based XxY1−xC (X, Y ≡ Si, Ge, Sn) Alloys

Abstract

Novel zinc-blende (zb) group-IV binary XC and ternary XxY1−xC alloys (X, Y ≡ Si, Ge, and Sn) have recently gained scientific and technological interest as promising alternatives to silicon for high-temperature, high-power optoelectronics, gas sensing and photovoltaic applications. Despite numerous efforts made to simulate the structural, electronic, and dynamical properties of binary materials, no vibrational and/or thermodynamic studies exist for the ternary alloys. By adopting a realistic rigid-ion-model (RIM), we have reported methodical calculations to comprehend the lattice dynamics and thermodynamic traits of both binary and ternary compounds. With appropriate interatomic force constants (IFCs) of XC at ambient pressure, the study of phonon dispersions offered positive values of acoustic modes in the entire Brillouin zone (BZ)—implying their structural stability. For XxY1−xC, we have used Green’s function (GF) theory in the virtual crystal approximation to calculate composition x, dependent and one phonon density of states . With no additional IFCs, the RIM GF approach has provided complete in the crystallographic directions for both optical and acoustical phonon branches. In quasi-harmonic approximation, the theory predicted thermodynamic characteristics (e.g., Debye temperature ΘD(T) and specific heat Cv(T)) for XxY1−xC alloys. Unlike SiC, the GeC, SnC and GexSn1−xC materials have exhibited weak IFCs with low [high] values of ΘD(T) [Cv(T)]. We feel that the latter materials may not be suitable as fuel-cladding layers in nuclear reactors and high-temperature applications. However, the XC and XxY1−xC can still be used to design multi-quantum well or superlattice-based micro-/nano devices for different strategic and civilian application needs.

Strain-Dependent Effects on Confinement of Folded Acoustic and Optical Phonons in Short-Period (XC)m/(YC)n with X,Y (≡Si, Ge, Sn) Superlattices

“…Ge . C) ∆ SLs, the perusal of Figure 3a,b reveals some interesting features: (a) in agreement with the existing results of phonon dispersions for binary zb SiC and GeC materials [146,154], our simulations of ω (q ⃗) in SiC/GeC SLs confirms the FAPs (see: Figure 3b) appearing between 0 to 350 cm −1 [the common overlapping acoustic phonon region of SiC-GeC] while the other acoustic modes fall in the frequency range of 350 to 630 cm −1 and behave as confined modes in the SiC layer, (b) the calculations of FAPs by M-LCM have corroborated the results derived earlier using Rytov s model (see: Table 2), (c) the FAPs are weakly affected by varying ∆, and (d) the COMs are significantly influenced by ∆ (≡ 3) causing downward (upward) shifts of higher (lower) frequency optical modes (cf. Section 3.1.5).…”

“…Recently, theoretical simulations of phonon dispersions ω (q ⃗) for the zb XC (X = Si, Ge, and Sn) materials have appeared in the literature [146,154]. A closer look confirms significant divergences in their optical and acoustical phonon branches.…”

“…Calculations of phonon dispersions ω (q ⃗) for the bulk zb XC, YC materials are available [146,154] along the high-symmetry directions in the BZ. With the appropriate bulk phonon frequencies, the necessary force constants of the M-LCM method are obtained to simulate ω (q ⃗) for ideal (XC)m/(YC)n SLs, considering m = n = 10.…”

“…In the lack of such data for novel C-based (XC)m/(YC)n SLs, it is necessary to simulate Raman intensity profiles. Although the lattice dynamical calculations are known for the bulk SiC, GeC, and SnC materials [146,154], there exist either limited [153] or no reports for comprehending the phonon dispersions ω (q ⃗) of their SLs. To understand the impact of interfacial layer thickness on ω (q ⃗) as well as on Raman spectra, we presented here our systematic results for both the ideal (XC)m/(YC)n and graded (XC) ∆ /(X .…”

“…Except for a preliminary report [153], no methodological studies are available on the phonon dispersions ω q ⃗ of novel strained layer XC /(YC) SLs, especially for comprehending the prospects of FAPs, COMs, and IPMs. Due to the large lattice mismatch between SiC-GeC (~5.0%), GeC-SnC (~10.5%), and SiC-SnC (~15.0%) [154], one would expect stress in the planes parallel and perpendicular to the SL interfaces. The optical and electrical processes in GaN-, AlN-, and InN-based MQWs and SLs are remarkably influenced by the existence of graded interfaces [155].…”