“…At temperatures higher than about 350 K, other scattering mechanisms interplay and could even become predominant over the grain boundary one . Other authors have also reported kinks in the ln[σ( T ) T 1/2 ] vs T -1 dependencies in temperature ranges from 350 to 390 K. , Therefore, only the first crystal boundary activation energy may be considered as accurate enough in the sense of being free of contributions from other scattering mechanisms, while the other values should be considered with caution. 4 Plot of ln(σ T 1/2 ) vs 1/ T in the temperature interval from 25 to 310 °C, constructed from the temperature-dependent conductivity data for a nanocrystalline SnSe thin film sample.…”
Charge-carrier transport properties in chemically deposited thin films composed of close-packed tin(II) selenide
nanocrystals were studied both in the dark and under conditions when internal photoelectric effect is manifested
in the nanostructured material. Stationary and time-resolved experiments were performed to characterize the
photophysics of quantum-confined nanocrystals synthesized in thin film form. The charge-carrier transport
through the films was found to occur predominantly by the thermionic emission mechanism in temperature
range from 300 to 585 K. The corresponding crystal boundary barrier height in the case of as-deposited films
is ≈160 meV, and the trap states which cause a partial charge-carrier depletion of the nanocrystals are situated
below the Fermi level. Thermal band gap energy was found to be 0.90 eV, which is somewhat lower than the
value calculated from optical spectroscopic data (1.10 eV). A physical basis for these differences is proposed.
Both the internal photoelectric effect and the crystal boundary barrier height modulation upon illumination
were found to contribute to the photoresponse of nanocrystalline films, the surface and bulk recombination
velocities being comparable. Indirect and direct band gap energy values of 1.23 and 1.54 eV were calculated
for the nanocrystalline films on the basis of photoresponse data. The nonequilibrium conductivity was found
to relax exponentially with a time constant of 1.78 ms, which corresponds to the average lifetime of minority
charge carriers (electrons). Lux-ampere characteristics of the films further support the linear photoconductivity
relaxation mechanism, contrary to what is usually found in the case of amorphous materials.
“…At temperatures higher than about 350 K, other scattering mechanisms interplay and could even become predominant over the grain boundary one . Other authors have also reported kinks in the ln[σ( T ) T 1/2 ] vs T -1 dependencies in temperature ranges from 350 to 390 K. , Therefore, only the first crystal boundary activation energy may be considered as accurate enough in the sense of being free of contributions from other scattering mechanisms, while the other values should be considered with caution. 4 Plot of ln(σ T 1/2 ) vs 1/ T in the temperature interval from 25 to 310 °C, constructed from the temperature-dependent conductivity data for a nanocrystalline SnSe thin film sample.…”
Charge-carrier transport properties in chemically deposited thin films composed of close-packed tin(II) selenide
nanocrystals were studied both in the dark and under conditions when internal photoelectric effect is manifested
in the nanostructured material. Stationary and time-resolved experiments were performed to characterize the
photophysics of quantum-confined nanocrystals synthesized in thin film form. The charge-carrier transport
through the films was found to occur predominantly by the thermionic emission mechanism in temperature
range from 300 to 585 K. The corresponding crystal boundary barrier height in the case of as-deposited films
is ≈160 meV, and the trap states which cause a partial charge-carrier depletion of the nanocrystals are situated
below the Fermi level. Thermal band gap energy was found to be 0.90 eV, which is somewhat lower than the
value calculated from optical spectroscopic data (1.10 eV). A physical basis for these differences is proposed.
Both the internal photoelectric effect and the crystal boundary barrier height modulation upon illumination
were found to contribute to the photoresponse of nanocrystalline films, the surface and bulk recombination
velocities being comparable. Indirect and direct band gap energy values of 1.23 and 1.54 eV were calculated
for the nanocrystalline films on the basis of photoresponse data. The nonequilibrium conductivity was found
to relax exponentially with a time constant of 1.78 ms, which corresponds to the average lifetime of minority
charge carriers (electrons). Lux-ampere characteristics of the films further support the linear photoconductivity
relaxation mechanism, contrary to what is usually found in the case of amorphous materials.
“…Furthermore CdS has remained a focus of the material science community due to its important band gap, conversion efficiency, high absorption coefficient, stability and last but not the least its significantly low cost [8]. The current transport mechanisms in CdS thin films have been reported [9] and there exists a vast literature covering theoretical and experimental studies of electronic band structure [10]. CdS has a wide and direct band gap (2.42 eV), ntype semiconducting material [11] and found in two crystalline forms; cubic (zinc-blend) phase and hexagonal (wurtzite) phase.…”
“…In other words, it should overcome the potential barrier ϕ(x). In Seto's model, this energy is given in the case of thermionic emission as (3) where q is the carrier charge, and ε is the film permittivity. Furthermore, the grain conductivity in this model can be obtained as (4) where L is the grain length (size).…”
Section: Comparison With Theoretical Resultsmentioning
confidence: 99%
“…Many researchers have focused their work on the enhancement of the optical and electrical properties of pure and doped CdS films to produce high efficiency solar cells. [1][2][3] This enhancement has been in progress for some time now and the efforts to deposit large-grain CdS films on low cost substrates are still ongoing. In general, it has been realized that mixing CdS with chlorine has a substantial effect on the electrical properties of these films.…”
The CdS:Cl thin films have been prepared using thermally evaporated, CdCl 2 -mixed CdS powder at 200°C substrate temperature. The percentage of CdCl 2 in the mixture varied from 0% to 0.20%. The electrical properties and the grain size of the deposited films were investigated. The results show that light doping, resistivity, carrier concentration, and mobility follow Seto's model for polycrystalline material. However, with heavy doping, these properties undergo a saturation trend. The saturation behavior can be understood in terms of the rapid formation of the A-center complexes in the films. The deposited films were annealed at 250°C and 300°C.The resistivity of pure and lightly doped CdS films increased with annealing temperature, whereas carrier concentration and mobility in these films decreased. However, for the higher doping concentrations, the resistivity decreased, whereas carrier concentration and mobility showed improvement. These changes in electrical properties of the deposited films with annealing and doping concentration are attributed to a reduction in the lattice defect sites in CdS upon annealing. The experimental results are interpreted in terms of a modified version of Seto's model for polycrystalline materials.
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