Investigation of optical, electrical and optoelectronic properties of SnSe crystals

Abstract

The optical, electrical and optoelectronic properties of tin selenide crystals are of immense significance for application in photodetectors and energy conversion and storage devices. The transition metal chalcogenides possess a layered structure that interacts with each other through van der Waal forces and can also offer sites for intercalation. The low molecular weight materials like GeSe and SnSe are found in an orthorhombic structure. In this article, the optical, electrical and optoelectronic properties of as-grown tin selenide crystals are investigated. The chemical composition of the crystals grown with the aid of direct vapour transport (DVT) technique is confirmed through energy Dispersive analysis of X-rays (EDAX), at the same time the morphological analysis is accomplished using optical microscopy and Scanning Electron Microscopy (SEM). The grown crystals are characterized by powder X-ray diffraction (XRD) method to assess the structural properties of the material. The XRD evaluation found out the orthorhombic structure of the crystals with the space group 2h16D (Pcmn) having lattice parameters a = 11.490 A, b = 4.440 A and c = 4.135 A. The crystallinity of grown samples was verified by transmission electron microscopy (TEM). The single crystalline nature of grown crystals was revealed by SAED pattern. The indirect optical band gap of 1.0065 eV, Urbach energy and steepness parameter are calculated utilising UV–VIS-NIR spectrophotometer. The optical absorption of as-grown SnSe crystals has been measured close to the fundamental absorption edge at room temperature. Both types of transitions, i.e. direct and indirect, are involved in the absorption process. Electrical transport properties like resistivity measurements (parallel and perpendicular path to the c-axis) had been carried out on these crystals within the temperature range 297–673 K. Anisotropy in resistivity measurements in both the directions, i.e. parallel and perpendicular direction to the c-axis was discovered. The p-type semiconducting nature was confirmed with the aid of Hall-effect measurements. For the photodetection properties of SnSe crystals, light source (670 nm) having an intensity of 3 mW/cm2 at distinctive biasing voltages is used. The outstanding detection properties are revealed from the responsivity, specific detectivity and external quantum efficiency (EQE) of pure SnSe crystals.