Variable-Range Hopping and Thermal Activation Conduction of Y-Doped ZnO Nanocrystalline Films

Abstract

ZnO and Y-doped ZnO nanocrystalline films were separately fabricated on the glass substrates by sol-gel spin-coating method. X-ray diffraction patterns of the films show the same wurtzite hexagonal structure and (002) preferential orientation. SEM images show that grain size and thickness of the nanocrystalline films decrease with increasing doping concentration. The decrease of optical bandgap with the increase of Y doping is deduced from the transmittance spectra. Temperature-dependent resistivity reveals a semiconductor transport behavior for all ZnO and Y-doped ZnO nanocrystalline films. The resulting conductivity originates from the combination of thermal activation conduction and Mott variable range hopping (VRH) conduction. In the high temperature range, the temperature-dependent resistivity can be described by the Arrhenius equation, σ(T)=σ 0 exp[-(E a /kT)], which shows the thermal activation conduction. The activation energy E a increases from 0.47 meV for ZnO film to 0.83 meV for Zn 0.98 Y 0.02 O film. On the contrary, in the low temperature range, the temperature-dependent resistivity can be fitted well by the relationship, σ(T)=σ h0 exp[-(T 0 /T) 1/4 ], which indicates the behavior of Mott VRH. The results demonstrate that the crystallization and the corresponding carrier transport behavior of the ZnO and Y-doped ZnO nanocrystalline films are affected by Y doping.

The influence of Y contribution on crystallographic, topographic and optical properties of ZnO: A heterojunction diode application

“…The E g values for pure and Y incorporated ZnO samples are a good agreement with values varied between 3.151 eV and 3.42 eV for Ga, In, Al and B doped ZnO samples [32,[36][37][38]. Unlike our results, Lin et al [25] found that E g value for pure ZnO dropped off from 3.2827 eV to 3.2656 eV with Y contribution in a sol-gel spin coating study. However, in another sol-gel dip coating study made by Yu et al [18], it was found that 0.5 at.% Y doping caused an increase in E g of pure ZnO from 3.30 eV to 3.37 eV and more Y doping brought about a decrease in the optical band gap.…”

“…It is seen a shift to the small angles with Y doping. A shift to small angles with Y doping was also found by Lin et al [25] and Anandan and Muthukumaran [12]. The interplaner distance values (d) for each peak are determined with Bragg's law and interplaner distance values continuously increased with Y doping ratio.…”

“…Pure and Y doped ZnO structures may be deposited with several chemical and physical growth methods such as hydrothermal method, spray pyrolysis, sol-gel spin coating, DC magnetron sputtering, electrochemical deposition, and pulsed laser deposition [4,[24][25][26][27][28]. The sol-gel spin coating is a very appropriate thin film fabrication technique owing to its low costs, simplicity [29], the capacity of homogenous film production [30], and easy intervention [31].…”

A novel WS2 nanowire-nanoflake hybrid material synthesized from WO3 nanowires in sulfur vapor

“…ln ( R ) vs. T −1 ) gives an excellent fit for our dataset with a reasonable barrier of 0.29 eV obtained from the slope of the fitting parameter, thus thermally activated conduction is a plausible mechanism. Note, the variable range hopping model for 3-dimensional conduction (in which ln ( σ ) is linearly proportional to T −1/4 , where σ is the conductivity) 30 31 fits also very well (not displayed here) to our data. However the extracted values for localization length as well as density of electronic states are unphysical thus this latter model for the conduction mechanism may be ruled out.…”

Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS2 Crystals

“…For n -type semiconductors, the conduction process is mainly contributed by electrons that transition from the donor level to the conduction band. The relationship between resistivity ρ and temperature T can be expressed as [ 29 , 61 , 62 , 63 ] where ρ 0 is a constant, k B is the Boltzmann constant, and E a is the activation energy, which approximately measures the energy difference between the bottom of the conduction band and the donor level. The lower the activation energy, the easier it is for the donor electrons to jump to the conduction band.…”