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

Single crystals of β-In2S3 were grown by chemical vapor transport method using ICl3 as a transport agent. The below and above band-edge transitions in β-In2S3 have been characterized using optical absorption and photoluminescence (PL) measurements in the temperature range 20-300 K. Thermoreflectance (TR) and photoconductivity (PC) measurements were carried out to verify the band-edge nature of the diindium trisulfide tetragonal crystals. Experimental analyses of the transmittance, PL, PC, and TR spectra of β-In2S3 confirmed that the chalcogenide compound is a direct semiconductor with a band gap of about 1.935 eV at 300 K. β-In2S3 is familiar with its defect nature. For the β-In2S3 crystals, two defect emissions and two above band-edge luminescences were simultaneously detected in the PL spectra at low temperatures. The energy variations of the defect emissions showed temperature-insensitive behavior with respect to the temperature change from 20 to 300 K. Temperature dependences of transition energies of the near-band-edge (NBE) transitions below and above band gap are analyzed. The origins for the NBE transitions in the β-In2S3 defect crystals are discussed.