Optical and electronic properties of lead sulfide spherical nano particle

Abstract

In this paper optical and electronic properties of lead sulfide spherical nano particle are studied using the density functional theory. To this end, a lead sulfide unit cell with Fm-3 m(225) symmetry is converted to a 1 nm spherical nanocluster, and then is placed into a 2 nm supercell structure. Total density of state (DOS) and partial density of states (PDOS) are considered to study electronic properties. The highest energy level of the valence band and its lowest energy level originate from 3p of sulfur atom and 5d of Lead atom respectively. The absorption coefficient, conductivity, dielectric function, loss function, reflective index, and reflectivity spectrum are studied to investigate optical properties for radiation power up to 35 eV. The analyses identify that the imaginary part of dielectric function has two main regions representing the ohmic resistance of PbS at the regions. The real part of the dielectric function has a static dielectric constant of 6.5 (ε(0) = 6.4) representing the plasma frequency of lead sulfide spherical nano particle. Moreover, the material has maximum light absorption for photons with 10 eV energy which relates to the ultraviolet spectrum. However, it shows considerable absorption for photons with 5 eV and 30 eV energy. The static refractive index is found to be 2.5 (n(0) = 2.5) and maximum refractivity occurs in the visible region for photons with energy less than 3 eV. Analysis of the conductivity of lead sulfide spherical nano particle shows that it is a semiconductor material with a significant loss for photons with 2−6 eV energy at the visible range.

Introduction

Lead sulfide (PbS) is a narrow bandgap semiconductor which has attracted considerable attention of researchers. Varieties of photonic, optoelectronic and electronic devices have been designed and fabricated based on different forms of PbS (i.e., bulk, nanocrystal, nanosheets, and … PbS). Optical waveguides [1], optical fiber amplifiers [2], lasers [3], heterojunction photovoltaic devices [4], photon detectors [5,6], solar cells [[7], [8], [9]], saturable absorbers for passive Q-switching [10], gas sensors [11], and thin-film transistor gas sensors [12] are some examples of photonic, optoelectronic and electronic devices based on different forms of PbS.

Nanostructures have attracted great interest in recent years because of their unique electrical, physical, optical, and transport properties that are different from the bulk materials [13,14]. Several researches have been devoted to identifying structural characteristics of PbS but to the best of our knowledge, optical and electronic properties of PbS spherical nano particle have not yet been studied. Preobrajenski, and Chasse reported on the atomic and electrical structure of epitaxial PbS on InP [15]. The electronic structure of nanocluster PbS was studied theoretically by Kane et al. [16]. Properties of PbS nanostructure thin film were reported in 2014 [17]. Kim et al. investigated the impact of stoichiometry on the electronic structure of PbS quantum dots [18]. Characteristics of embedded PbS nanocrystal in zirconia sol-gel film were reported in reference [19]. The properties of PbS nanowires and nanorods are studied by Saraidarov et al. [20]. Li et al. reported the nonlinear optical properties of PbS nanoparticles [21]. The impact of Cu doping on the electronic and optical properties of PbS thin films was investigated by Touati et al. [22]. In our previous article, the characteristics of bulk PbS is studied and we showed that it shows good absorption and reflection for ultraviolet electromagnetic waves [23]. In this research, optical and electronic properties of PbS spherical nano particle are analyzed and reported. The reported electronic and optical properties of PbS spherical nano particle can be used in the designing, modeling, and simulating the operation and evaluating the performance of electrical sensors and optoelectronic device based on the PbS nano particle. The calculation method is explained in section two. Section three provides theoretical results and discussions about optical and electronic properties of PbS spherical nano particle. Section four ends the paper with the conclusion and summarizing the results.