Optical-absorption study of synthetic pyrite FeS2 single crystals

Abstract

The optical-absorption study of synthetic pyrite FeS2 single crystals prepared by the chemical-vapor-transport method is reported over a temperature range from 4.2 to 300 K. At lower temperatures several features which occur below the absorption edge are superposed on the absorption curve. The origin of the sharpest peak is identified as the transition between the top of valence band and Cr3+ trapping center through comparison of the results with that of the low-temperature photoconductivity and the photoelectron paramagnetic resonance measurements. The nature of other weaker features is discussed. The existence of these features prevents the determination of the band gap of FeS2 by fitting the optical-absorption data to the form of (αhν)∝(hν−E0)n. Therefore, the energy gap of FeS2 at low temperatures is estimated by adding the thermal ionization energy of the shallow acceptor states to the photoionization energy between the (SCl)2− states and the bottom of the conduction band. The band gap of various temperatures is determined and its temperature dependence is analyzed by an empirical expression proposed by O’Donnell and Chen [Appl. Phys. Lett. 58, 2924 (1991)]. The parameters that describe the temperature dependence of Eg of the material are evaluated and discussed.

Characterization of near band-edge properties of synthetic p-FeS2 iron pyrite from electrical and photoconductivity measurements

“…5, the roomtemperature photoconductive band gap by using the Moss rule is determined to be 0.87 ± 0.02 eV. This value is in good agreements with the values of 0.83 ± 0.02 eV reported by Tsay et al [16], 0.93 eV by Yang et al [7], and 0.91 ± 0.1 eV by Bither et al [8]. As shown in Fig.…”

“…The solid curves are the experimental PC spectra measured at the temperatures of 10, 77, 200, 250, and 300 K, respectively. Observing the low-temperature PC spectra of 10 and 77 K, the impurity feature of Cr 3+ and the other imperfection peaks that were found in previous absorption and photoconductivity measurements of FeS 2 [7,15,16] were not obvious in the sample. The 6.…”

“…Single crystals of iron pyrite FeS 2 were grown by the chemical vapor transport method [1,7,17] using ICl 3 as a transport agent. Prior to the crystal growth, quartz tubes containing ICl 3 and the elements (Fe: 99.95% pure, S: 99.999%) were evacuated and sealed.…”

“…The impurity and defect effects of synthetic FeS 2 crystals had been characterized using the techniques of photo-paramagneticresonance (photo-EPR) [14], optical absorption [7], and photoconductivity measurements [15]. Some of unintentional Cr 3+ and Ni 2+ impurities and a (SCl) 2− defect were detected in the chalcogen-deficient FeS 2 crystals.…”

“…erties of FeS 2 , it is necessary to carry out a fundamental study on the synthetic compound with a controlled level of impurities and stoichiometry. High-purity synthetic FeS 2 can be grown by the chemical vapor transport method [1,7] and has been studied quite extensively both in synthetic form as well as in natural form [8][9][10][11]. From electrical measurements, both n-and p-type conduction behavior had been observed in natural crystals [12], whereas most of the synthetic FeS 2 crystals revealed n-type conductivity, but only one case (i.e.…”