Above‐band gap optical excitation of non‐centrosymmetric semiconductors can lead to the spatial shift of the center of electron charge in a process known as shift current. Shift current is investigated in single‐crystal SnS2, a layered semiconductor with the band gap of ≈2.3 eV, by THz emission spectroscopy and first principles density functional theory (DFT). It is observed that normal incidence excitation with above gap (400 nm; 3.1 eV) pulses results in THz emission from 2H SnS2() polytype, where such emission is nominally forbidden by symmetry. It is argued that the underlying symmetry breaking arises due to the presence of stacking faults that are known to be ubiquitous in SnS2single crystals and construct a possible structural model of a stacking fault with symmetry properties consistent with the experimental observations. In addition to shift current, it is observed THz emission by optical rectification excited by below band gap (800 nm; 1.55 eV) pulses but it requires excitation fluence more than two orders of magnitude higher to produce same signal amplitude. These results suggest that ultrafast shift current in which can be excited with visible light in blue–green portion of the spectrum makes SnS2a promising source material for THz photonics.
Previous band structure calculations predicted Ag3AuSe2to be a semiconductor with a band gap of approximately 1 eV. Here, we report single crystal growth of Ag3AuSe2and its transport and optical properties. Single crystals of Ag3AuSe2were synthesized by slow‐cooling from the melt, and grain sizes were confirmed to be greater than 2 mm using electron backscatter diffraction. Optical and transport measurements reveal that Ag3AuSe2is a highly resistive semiconductor with a band gap and activation energy around 0.3 eV. Our first‐principles calculations show that the experimentally determined band gap lies between the predicted band gaps from GGA and hybrid functionals. We predict band inversion to be possible by applying tensile strain. The sensitivity of the gap to Ag/Au ordering, chemical substitution, and heat treatment merit further investigation.
more » « less- Award ID(s):
- 1720633
- PAR ID:
- 10369668
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Zeitschrift für anorganische und allgemeine Chemie
- Volume:
- 648
- Issue:
- 15
- ISSN:
- 0044-2313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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