Structural, optical, electrical and low temperature thermoelectric properties of degenerate polycrystalline Cu₇Se₄ thin films

Abstract

Polycrystalline copper selenide thin films of composition Cu7Se4 with thickness of the order of 350 nm are deposited on glass substrates at a temperature of 498 ± 5 K and pressure of 10−5 mbar using reactive evaporation with high purity copper (99.999%) and selenium (99.99%) as the elemental starting materials. X‐ray diffraction (XRD) shows the formation of Cu7Se4 thin films. Structural parameters such as lattice constant, particle size, dislocation density, number of crystallites per unit area and strain in the film are evaluated. The surface morphology and composition of the film are studied using 2D and 3D atomic force microscopy (AFM) and energy dispersive analysis of X‐rays (EDAX), respectively. Hall effect measurement is done at room temperature to determine the conductivity type, carrier concentration, carrier mobility and Hall coefficient of the film. The carrier concentration of the film at room temperature is found to be nearly 1021 cm−3 suggesting that the prepared films are degenerate semiconductors. The films possess a direct allowed transition with an optical band gap of 2.25 eV. High reflectance and low transmittance of the film in the near‐infrared region – a behaviour, which is typical of degenerate semiconductors is related to its high electrical conductivity (∼103 Ω−1 cm−1). Temperature variation of thermoelectric power (TEP) and electrical conductivity also suggests degenerate semiconductor like behaviour of the film. The observed positive Seebeck coefficient indicates p‐type conduction mechanism. The data from the analyses of Hall measurements and TEP have been combined to evaluate important material parameters such as mean free path, relaxation time, Fermi energy and effective mass. Certain possible applications of the prepared film in various fields are also discussed.

Structural, surface morphological, optical and thermoelectric properties of sol–gel spin coated Zn doped CdS thin films

“…It is also noticed that the Seebeck coefficient of the films increases with the temperature, which is consistent for a degenerate semiconductor. This observation is in well agreement with the general fact that higher conductivity exhibits low thermoelectric power [36].…”

Optical and low-temperature thermoelectric properties of phase-pure p-type InSe thin films

“…This technique provides stoichiometric films with excellent reproducibility, uniform deposition, large-area production and high deposition rate. The detailed experimental procedure has been described elsewhere [18]. Briefly, high-purity indium (99.999 %) and selenium (99.99 %) were evaporated simultaneously at suitable rates from two independently heated sources and were allowed to deposit on glass substrates kept at an elevated temperature of 473 ± 5 K. The deposition of thin film was carried out at a pressure of 10 -5 mbar.…”

“…The average crystallite size of the prepared InSe thin film was calculated using Scherrer equation [20] and was obtained as 48 ± 2 nm. The microstructural parameters such as dislocation density, number of crystallites per unit area and lattice strain in the film were estimated as 4.34 9 10 10 lines cm -2 , 15.37 9 10 10 cm -2 and 1.8 9 10 -3 , respectively [18]. Figure 2 shows the EDAX spectrum of the prepared InSe thin film.…”

“…The absorption coefficient (a) showed a high value of about 10 5 cm -1 , suggesting the possible use of the film as absorber layers in solar cells. The optical band gap of the film was determined using the well-known Tauc relation [18]. Figure 5a illustrates the (ahm) 2 versus hm plot of phase-pure InSe thin film.…”

Structural, morphological, optical and electrical properties of Cu0.87Se thin films coated by electron beam evaporation method

“…Okimura et al [6] prepared Cu 2-x Se-Si junction by conventional vacuum evaporation method and reported that the conversion efficiency of the junction is about 8.3 and 8.8 % for 3-and 2-mm-diameter Cu 2-x Se layer, respectively. Several chemical and physical methods such as chemical bath [2,[7][8][9][10][11], aerosol-assisted chemical vapor deposition [12,13], electroless [14], solgel [15], electrochemical deposition [16], electrophoretic deposition [17], brush electroplate deposition [18], cathodic deposition [19], dip coating [20], spray pyrolysis [21], vacuum co-evaporation [22], vacuum evaporation [6,23], pulsed laser deposition [4,24], selenization [25], magnetron sputtering [26], flash evaporation [27] and reactive evaporation [28] methods have been employed to deposit copper selenide thin films. Ting and Lee [17] prepared Cu 2-x Se nanocrystals by one-pot solution-phase method.…”