Growth and characterization of near-band-edge transitions in β-In2S3 single crystals

Sulfurization-induced growth of single-crystalline high-mobility β-In2S3 films on InP

“…Peak A was attributed to a radiative process involving the surface oxide (β-In 2 S 3(1-x ) O 3x ) or sulfur vacancyrelated states, and peak B was ascribed to the band edge emission of β-In 2 S 3 or a related donor-acceptor transition of an indium-rich phase. 12,22 Finally, peak C most likely corresponded to a higher energy state correlated with S 3p and In 5s states, and was also observed for ALD-grown polycrystalline β-In 2 S 3 films. 8,23 Importantly, no mid-gap states (1.5-1.6 eV) corresponding to intrinsic defects were observed.…”

“…Prior studies reported that the direct and indirect bandgaps of β-In 2 S 3 films varied within the ranges of 1.9-2.75 and 1.98-2.2 eV, respectively. 12,20,21 Additionally, Ho showed that single-crystalline tetragonal β-In 2 S 3 exhibits two dominant near-band-edge transitions, corresponding to direct bandgaps of 1.935 and 2.19 eV, as well as two defect state transitions with energies of 1.528 and 1.581 eV. 12 At RT, the PL spectra of β-In 2 S 3 films deposited on InP featured a broad peak at 400-800 nm (Fig.…”

“…Importantly, tetragonal β-In 2 S 3 thin films exhibit a wide range of bandgaps (1.64-3.7 eV) 10,11 e.g., a direct bandgap of 1.9 ± 0.3 eV was recently determined by photoluminescence (PL) and photoconductivity measurements. 8,12,13 Crystalline β-In 2 S 3 thin films exhibit n-type conductivity and feature carrier concentrations of 10 15 -10 18 cm -3 and mobilities of 0.2-5 (polycrystalline) or 100 cm 2 V -1 s -1 (single-crystalline). 8,14,15 Although highly crystalline tetragonal β-In 2 S 3 films can be prepared using atomic layer deposition (ALD), 8 In view of the scarce information on chemical vapor deposition-grown highly crystalline In 2 S 3 films, we herein used metalorganic chemical vapor deposition (MOCVD) to grow tetragonal singlecrystalline β-In 2 S 3 films on InP and characterized their structure and electrical characteristics by scanning electron microscopy (SEM), field emission SEM, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, scanning transmission electron microscopy (STEM), and Hall mobility measurements.…”

“…12,20,21 Additionally, Ho showed that single-crystalline tetragonal β-In 2 S 3 exhibits two dominant near-band-edge transitions, corresponding to direct bandgaps of 1.935 and 2.19 eV, as well as two defect state transitions with energies of 1.528 and 1.581 eV. 12 At RT, the PL spectra of β-In 2 S 3 films deposited on InP featured a broad peak at 400-800 nm (Fig. 4b), which could be deconvoluted into peaks A, B, and C at 574.7 (2.15), 648.5 (1.91), and 464.3 nm (2.67 eV), respectively, using Lorentzian fitting.…”

“…12 Further study including variable temperature (40-300K) steady-state PL analysis will be necessary to clarify the Varshini parameters. The electrical properties of β-In 2 S 3 films were probed by Hall measurements, which determined the charge carrier concentration (electrons, n-type), Hall mobility (µ H ), and resistivity (ρ) of as-grown In 2 S 3 films as 4.9 × 10 15 cm -3 , 1810.9 cm 2 V -1 s -1 , and 0.704 Ω cm, respectively.…”