The direct bandgap of gray α-tin investigated by infrared ellipsometry

Abstract

Using Fourier-transform infrared ellipsometry, the authors provide spectroscopic evidence about the valence band (VB) structure of diamond-like α-tin. The mid-infrared dielectric function of α-tin grown pseudomorphically on InSb or CdTe by molecular beam epitaxy shows a strong E¯0 peak near 0.41 eV. This peak is assigned to allowed intravalence band transitions from the Γ7− (electron-like) VB to the Γ8+v heavy hole VB and/or interband transitions from Γ7− to the Γ8+c light “hole” conduction band. The strength of this peak requires a hole density in the mid-1018 cm−3 range at room temperature, which might be caused by unintentional doping, by thermal electron-hole pair generation, or by the possibility that the L6+ conduction band might have an energy slightly lower than the Γ8+ VB maximum. Alternatively, this E¯0 peak might be enhanced by the M-shape of the Γ7− VB caused by interactions with the Γ7+ split-off hole VB. A sum-rule analysis of the dielectric function between 0.16 and 6.5 eV is consistent with a high-frequency dielectric constant of 24, which has at most a weak temperature dependence between 100 and 300 K.

Reversed Phase Transformation of β→α-Sn at Elevated Temperatures towards Quantum Material Integration on Silicon

“…Samples with a significant amount of α-Sn (annealed at 350°C and 375°C) show an additional absorption edge at ∼1750 nm wavelength compared to those with no or little α-Sn, and the absorption further increases with the decrease of wavelength up to 1250 nm. This additional optical absorption feature at ∼0.7-1 eV caused by α-Sn is consistent with a recent work 48 , and it can be attributed to a transition corresponding to the spin-orbit splitting energy of ∆ 0 = Γ 8v − Γ 7v ≈ 0.7eV 1,48 . Moreover, it has been recently demonstrated that pulsed laser can be used to change the quantum states of 3D TDS 39 , so the measured absorption spectrum of α-SnGe suggests that commonly used lasers for telecommunications at 1310-1550 nm may be used for quantum state switching with potential for integration with silicon integrated photonics.…”

Mid-infrared (3–8 μm) Ge1−ySny alloys (0.15 < y < 0.30): Synthesis, structural, and optical properties

“…19), but the discrepancy should be interpreted with caution because the E0 transition in α-Sn has a unique line shape that is not fully understood. 29 The difference between the LC&L prediction and the best fit in Fig. 6(b) has an important practical consequence: LC&L predict a vanishing band gap for y = 0.35, which implies that the 8-12 μm window could be easily covered with Ge-rich Ge1-ySny alloys.…”

Nonparametric Local Pseudopotentials with Machine Learning: A Tin Pseudopotential Built Using Gaussian Process Regression

“…For comparison, the electronic structure obtained with the semilocal ONV and GTH PP are given. α-Sn was characterized as zero-bandgap semiconductor, while other earlier experiments reported for α-Sn a bandgap of 0.08 eV . Besides this difference, it is clear that an accurate PP should produce a similar value (a zero or at least a very small bandgap) with a reasonable electronic broadening.…”