Bi Doped ZnO Films Research Articles

Effect of Bi dopant on morphological and optical properties of ZnO semiconductor films produced by the sol-gel spin coating process

Abstract In this study, undoped semiconductor ZnO thin film and Bi-doped ZnO thin films were produced using the sol-gel spin coating method. By changing each parameter of the spin coating method, the best conditions for the formation of the film were determined via the trial and error method. When the appropriate parameter was found, the specified parameter was applied for each film. The structural, superficial, and optical properties of the films produced were characterized via atomic force microscope (AFM), UV-visible spectroscopy, and Fourier transform infrared (FTIR), and the effects of Bi dopant on these properties were investigated. When the morphological properties of the undoped and Bi-doped ZnO films were examined, it was observed that they had a structure in a micro-fiber shape consisting of nanoparticles. When the surface roughness was examined, it was observed that the surface roughness values became larger as the rate of Bi dopant increased. By examining the optical properties of the films, it was determined that they were direct band transition materials and Bi-doped thin films were involved in the semiconductor range. In addition, optical properties changed positively with Bi dopant. Since Bi-doped ZnO thin film has a wide bandgap and good optical properties, it is a material that can be used in optoelectronic applications.

Optical and Electrical Characterization of Stable p-Type ZnO Thin Films Obtained by Bismuth Doping.

We report the growth of stable p-type ZnO thin films obtained by doping bismuth (Bi) in ZnO and deposited over ITO coated glass substrate. The Bi doped ZnO thin films have been deposited by a sol-gel spin coating method using zinc acetate and bismuth nitrate as main precursors. The structural, optical and electrical properties of annealed Bi doped thin films have been studied in detail using X-ray diffraction (XRD), Atomic force microscopy (AFM), ellipsometry, hot probe system and Hall measurement. The presence of strong diffraction peak along (101) obtained from the XRD spectra shows that the high-quality Bi doped ZnO nanostructures grow along (101) orientation. A number of important micro-structural parameters for the thin films such as grain size, lattice parameters, stress and texture coefficient have been calculated, in order to show the effect of Bi incorporation in ZnO thin film. Further, transmittance has been calculated over the range of 350- 800 nm wavelength regions. The optical band gap of Bi doped ZnO films have also been calculated for different concentrations of Bi using the data taken by an ellipsometer. Hot probe characterization method has been used to ascertain the type of semiconductor thin film and it was observed that films doped with the concentration of 10 mol% Bi show p-type nature that was found to be stable over the period of eight months. Further, in order to calculate the resistivity, hole concentration, and mobility of p-type Bi doped ZnO thin film Hall measurement have been performed.

Room temperature transparent conducting magnetic oxide (TCMO) properties in heavy ion doped oxide semiconductor

Bismuth doped ZnO (ZnBi0.03O0.97) thin films are grown using pulsed laser deposition. The existence of positively charged Bi, absence of metallic zinc and the Zn-O bond formation in Bi doped ZnO are confirmed using X-ray Photoelectron Spectroscopy (XPS). Temperature dependent resistivity and UV-visible absorption spectra show lowest resistivity with 8.44 × 10-4 Ω cm at 300 K and average transmittance of 93 % in the visible region respectively. The robust ferromagnetic signature is observed at 350 K (7.156 × 10-4 emu/g). This study suggests that Bi doped ZnO films should be a potential candidate for spin based optoelectronic applications.

Highly oriented and conducting Bi doped ZnO (BZO) layers chemically sprayed using nitrogen gas carrier

In this work, we have successfully prepared the highly conducting and transparent Bi doped ZnO (BZO) thin films using pneumatic spray pyrolysis technique with nitrogen (N2) carrier gas. The evolutions of structural, morphological and opto-electrical properties of the BZO films as a function of Bi concentration were analyzed. It is found that the films are uniform with no haze or visible clusters. X-ray diffraction shows that all the films were polycrystalline with hexagonal wurtzite structure, without secondary phases. All the BZO layers exhibit the classical preferential orientation of (002) plane and it changes in favor of (100) plane at 3wt% Bi. The BZO thin films showed 83% as a value of average optical transmittance in the visible region. The optical band gap values oscillated around 3.23 and 3.27eV. The SEM micrographs show clusters and nano-crystalline grains with special shape on the surface. The photoluminescence spectra of the films exhibits ultraviolet and green emissions. The electrical resistivity reaches a minimum value (8.4310−3Ωcm) at 1wt% Bi.

Influence of Bi concentration on structural and optical properties of Bi doped p-type ZnO thin films prepared by sol–gel method

This paper reports the growth of stable p-type ZnO film on p-Si substrate. The bismuth doped ZnO (Bi doped ZnO) thin films have been grown by sol–gel spin coating method followed by thermal annealing. The structural studies performed exhibits that Bi doped ZnO thin film possess highly crystalline nature with c-axis orientation. The electrical conductivity of the deposited film has been determined by Seeback voltage measurement and its stability has been studied as function of time. Interestingly it was observed that ZnO thin films retain p-type nature even after 150 days. Further, optical band gap and reflectance of Bi doped ZnO films have also been determined with varying concentrations of Bi using the data taken by ellipsometer.

Fabrication and characterization of Au/p-ZnO Schottky contacts

This paper reports the electrical characteristics of gold contacts on p-type ZnO thin films synthesized by spin coating the sol containing zinc acetate and bismuth nitrate as main precursors. The structural, morphological and optical properties of the deposited thin film have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and Ellipsometry, respectively. Further, hot probe measurement has been used to ascertain the type of deposited film and it was observed that films doped with the concentration of 10mol% Bi shows p-type nature that was found to be stable over the period of five months. Moreover, reflectance of the Bi doped ZnO with varying Bi concentrations, have also been calculated over the wavelength range of 300–800nm. The optical band gap of Bi doped ZnO films have also been determined for different concentrations of Bi using the data taken by ellipsometer. The gold (Au) contacts have been deposited on the p-ZnO thin films using low cost thermal evaporation method. Electrical parameters such as the reverse saturation current, barrier height and ideality factor have also been determined for Au/p-ZnO thin film based Schottky contact using conventional thermionic emission model and Cheung’s method. The conventional thermionic emission model yields barrier height ∼0.681eV and ideality factor ∼2.3 however Cheung method gives barrier height ∼0.556eV, ideality factor ∼2.186 and series resistance ∼923Ω. The present study establishes the fact that Cheung’s method can be the best and most realistic method for approximating the diode parameters including the effect of series resistance of the Au/p-ZnO Schottky diode under consideration.

Effect of annealing on the properties of Bi doped ZnO thin films grown by spray pyrolysis technique

The effect of annealing temperature on the structural, optical and electrical properties of transparent and conducting Bi doped ZnO (BZO) films deposited on glass substrate by spray pyrolysis technique was investigated. The BZO thin films were annealed in the temperature range from 450°C to 550°C for 4h in air atmosphere. The grain size of the BZO films increased with increasing annealing temperature. The annealed BZO films were electrically stable and there was a drastic change in the electrical conductivity after annealing. The films annealed at 500°C showed better conductivity and optical transmittance.

INFLUENCE OF ANNEALING TEMPERATURE ON CHARACTERISTICS OF BISMUTH DOPED ZINC OXIDE FILMS

In this study, Bismuth (Bi) doped ZnO thin films were deposited on quartz substrates by a sol-gel spin coating method and annealed at different annealing temperatures of 200, 300, 400, 500, 600 and 700°C, respectively. Structural and optical properties of nanocrystalline Bi-doped ZnO film on quartz were investigated by using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and UV-VIS spectrophotometer. The high annealing temperature of 700°C as a critical temperature causes the crystallographic reorientation plane in ZnO:Bi nanostructure mostly due to the initial formation of the polycrystalline phase with the inter-grain segregation of Bi dopant atoms. Bi-incorporating ZnO films with an increase in annealing temperature resulted in a blue wavelength shift of the photon absorption edge. The optical band gap of the films was increased from 3.27 eV to 3.34 eV. By decreasing the annealing temperatures from 700 to 200°C, the grain size of Bi-doped ZnO decreased from 18 nm to 8 nm. The effect of the annealing temperature on the electrical conductivity had been considered. The low electrical conductivity of 0.9 (Ω.cm)-1 was obtained for ZnO:0.2 film annealed at 600°C with good nano-crystallization. However, the Bi-doped ZnO films prepared by cost-effective spin coating technique provided to have a very high photon absorption coefficient (104-105 cm-1) and did not appreciably affect the optical transparency. ZnO films doped with 0.2% at. Bi can be used as a high resistive buffer layer for solar cell application.

Properties of ZnO:Bi thin films prepared by spray pyrolysis technique

Abstract Undoped and Bi doped zinc oxide thin films were deposited on glass substrate at 450 °C using spray pyrolysis technique. The X-ray diffraction studies shows that Bi doped ZnO films are polycrystalline hexagonal structure with a preferred orientation along (1 0 1) direction. Crystallites size of the films decreases with increasing doping concentration. Scanning electron microscope image shows change in the surface morphology. The composition of Zn, O and Bi elements in the undoped and Bi doped ZnO films were investigated by X-ray photoelectron spectroscopy. Bi doped ZnO thin films show a transparency nearly 75% in the visible region. The optical band gap of ZnO thin films reduces from 3.25 eV to 3.12 eV with an increase in Bi concentration from 0 to 5 at.% respectively. Electrical conductivity of ZnO thin films increased from 0.156 to 6.02 S/cm with increasing Bi dopant concentration from 0% to 5% respectively.

Preparation and optical properties of Bi doped ZnO thin films with (100) orientation by rf magnetron sputtering

Bi doped ZnO films with (100) orientation have been grown on glass substrates by rf magnetron sputtering followed by vacuum annealing at 400 °C for 3 h. X-ray diffraction (XRD) revealed that the film first growth along (002) direction was suppressed to form (100) plane with c-axis parallel to the substrate. After annealed at 400 °C for 3 h under vacuum, transmittance about 80% in visible region and near 100% absorption in UV region for (100) oriented Bi doped ZnO films are confirmed by the optical transmission spectra. The optical band gap is evaluated to be around 3.13 eV which is lower than (002) oriented films.

Bi-induced acceptor states in ZnO by molecular-beam epitaxy

Bi-doped ZnO films were grown on Si (111) substrates by molecular-beam epitaxy. X-ray photoelectron spectroscopy and diffraction measurements reveal that Bi was incorporated into ZnO films without any phase separation. Room-temperature Hall effect measurements show a significant reduction of electron concentration and an increase of resistivity for Bi-doped ZnO films. In addition, a 3.222eV photoluminescence emission was observed particularly in the Bi-doped ZnO films and was identified as a donor-acceptor pair transition by temperature-dependent and excitation power-dependent photoluminescence measurements. These results indicate the possibility of generating acceptor states by Bi doping.

Varistor performance of nanocrystalline Zn–Bi–O thin films prepared by reactive RF magnetron sputtering at room temperature

The Zn–Bi–O films were deposited by reactive radio frequency magnetron sputtering in oxygen atmosphere from ZnBi alloy target (wt% ratio Zn:Bi=9:1) on glass substrate at room temperature. The XRD patterns show that the films deposited on tin-doped indium oxide/glass substrates were nanocrystalline. The microstructure of Bi-doped ZnO films was studied by scanning electron microscopy in combination with energy dispersive X-ray spectroscopy. All the obtained layers had varistor-type non-linear current–voltage ( I– V) characteristics with low breakdown voltage varying from few tenths of a volt to few volts.