Ga Co-doped ZnO Films Research Articles

Optimization of photoelectric properties of transparent conductive B and Ga co-doped ZnO films for electrochromic applications

To improve the performance of electrochromic devices, it is urgently necessary to develop transparent indium-free conductive electrodes with high conductivity and transparency. In this study, thin films of Ga-doped ZnO (GZO) and B–Ga co-doped ZnO (BGZO) were prepared on glass substrates using the plasma-assisted atomic layer deposition (PEALD) technique, and their structural and optoelectronic properties were characterized. It is found that all thin films were consistent with hexagonal fibrous ZnO structure, and the surface morphology of the membrane was homogenous at nanoscale. UV spectroscopy analysis showed that the doping of B and Ga elements could increase the transparency of ZnO films. The electrical properties can be remarkably enhanced by doping with B and Ga elements. Further more, tungsten oxide (WO3) was deposited on the as-prepared BGZO films using magnetron sputtering method. We activated the sample by applying voltage and observed a color transition from transparent to dark blue. It has a modulation range of 65 % in the 633 nm spectrum and a coloring efficiency of 37.8 cm2C-1. This work opens up remarkable new opportunities for developing high-performance transparent conductive electrode in electrochromic devices.

Effect of GZO cap-layer thickness and post-annealing treatment on GZO/HGZO bi-layer films

Hydrogen and Ga-codoped ZnO (HGZO) films caped with different thickness of Ga-doped ZnO (GZO) films (0–80 nm) were prepared by RF magnetron sputtering at room temperature, and the influences of GZO layer thickness and post-annealing treatment on structural, electrical and optical properties of the GZO/HGZO bi-layer films were investigated. The results show that increasing GZO layer thickness weakens the (002) preferred orientation, decreases the crystallize size and increases compressive stress of the films. The electrically conductive properties of the films first enhance and then degrade with increase of GZO layer thickness, and the best conductive properties can be obtained at GZO layer thickness of 20 nm. As GZO layer thickness increases, transmittance in visible range (TVis) and bandgap (Eg) of the films show a decreased trend, but their Urbach energy (Eu) increases. The crystallite size of the films first greatly and then slightly increases with increasing annealing temperatures to 400 °C, and annealing atmosphere (air or vacuum) and time (10 min or 2 h) have little effect on the crystallite size at the same annealing temperature. With increasing annealing temperature, compressive stress greatly decreases firstly and then slightly decreases under vacuum annealing or converts to tensile stress under air annealing. The conductive properties of the films degrade after vacuum annealing for 2 h, but they degrade significantly even after air annealing for 10 min. Increasing GZO layer thickness can retard the decline of conductive properties of the films under vacuum annealing of 200–400 °C for 2 h or air annealing of 200–300 °C for 10 min. With increasing annealing temperature, the TVis of the films basically shows a trend of first increase and then decrease, and the Eg and Eu of the films basically decrease. After annealing at 400 °C, the decreased Eg and Eu values of films under air annealing are close for different annealing time, but they are larger than those under vacuum annealing. Basically, thicker GZO layer is more likely to restrain the decrease of Eg, but leads to obvious decrease of Eu. In addition, effect of hydrogen doping and out-diffusion, crystallize growth and stress relaxation mechanism under annealing, and carrier transport and Eg shift mechanisms are also discussed.

Ultrasonic spray pyrolysis-induced growth of highly transparent and conductive F, Cl, Al, and Ga co-doped ZnO films

In this paper, the ultrasonic spray pyrolysis (USP) technology, under normal pressure conditions was adopts in this study to deposited ZnO films. The cheap zinc acetate, ammonium fluoride, and gallium chloride was used as Zn source, F source, Ga source and Cl source, respectively for deposited F, Cl, Al and Ga co-doped ZnO (FCAGZO) films. The influence of substrate temperature (Ts) on the morphology, structure, optical and electrical properties of ZnO thin films was studied. X-ray diffraction analysis shows that the Ts does not change the crystal structure of the ZnO film, and all films have a hexagonal wurtzite structure. With increase of Ts only the preferred orientation of the film changes from (100) to (002). X-ray photoelectron spectroscopy further confirmed the successful doping of ZnO by F, Cl, Al, and Ga, which accounts for the enhancement in carrier concentration in the FCAGZO films over that of pristine ZnO. As Ts increases, the resistivity first decreases, and then gradually increases. When the optimal substrate temperature Ts = 400 °C, the prepared FCAGZO film has a resistivity of 1.47 × 10-3 Ωcm when rapid heat treatment in N2 atmosphere at 750 °C, and the average transmittance exceeds 85% in the range of 400–1400 nm.

Sn–Ga co-doping in sol-gel derived ZnO thin films: Studies of their microstructural, optical, luminescence and electrical properties

Sn–Ga co-doped ZnO films with different proportions synthesized by the sol-gel spin-coating technique have been investigated for their microstructural, optical, luminescence, and electrical properties using a variety of characterization techniques. All the films exhibit c-axis orientation along the (0 0 2) plane having a hexagonal wurtzite structure of zinc oxide. The crystallinity of the films improves upon doping and co-doping. Morphological images reveal that the films possess the granular morphologies with varying features. The co-doped films have a higher root mean square (RMS) roughness in comparison to the undoped and doped ZnO films. In general, relative to the undoped film, the transmittance of the film improves upon doping and co-doping. The direct energy band-gap has a maximum value of 3.26 eV for the undoped ZnO film, which decreases upon doping and co-doping. In the visible region, the refractive index exhibits a minimum value of 2.12 for the 1T3GZO film at the wavelength of 600 nm. The photoluminescence spectra of the films consist of one near-band edge (NBE) emission peak related to the recombination of free excitons, and a few broad emission peaks linked to the native defects in the films. Among the co-doped ZnO films, the 1 at% Sn–Ga co-doped film (1T1GZO) has the optimum transmittance and electrical conductivity.

Optimization of physical properties of transparent conductive F and Ga co-doped ZnO films for optoelectronic applications

Highly transparent conductive F and Ga co-doped ZnO films were deposited on a glass substrate with radio frequency magnetron sputtering at various growth temperatures. Growing the films at a substrate temperature of 480 °C produced the lowest resistivity of 6.84 × 10−4 Ωcm, a carrier concentration of 2.3 × 1020 cm−3, and a mobility of 39.7 cm2/Vs. These parameters were significantly improved to 3.53 × 10−4 Ωcm, 3.08 × 1020 cm−3, and 57.5 cm2/Vs, respectively, after a rapid thermal annealing treatment. All the films showed a high average transmittance of 90% in the optical range 380–1400 nm.

B-doping and annealing on the properties of B and Ga co-doped ZnO films

Transparent conducting boron (B) and gallium (Ga) co-doped ZnO (BGZO) films were deposited by radio frequency (RF) magnetron sputtering. The influence of B-doping and annealing treatment on properties of BGZO films was investigated. The results indicate that all samples have hexagonal wurtzite structure with (002) preferential orientation and the film crystallinity is improved with increasing annealing temperature. The hall mobility of films increases and the carrier concentration decreases with the increasing of annealing temperature. The films also show red shift of the optical bandgap with the increasing of annealing temperature. The incorporation of B increases the thermal stability of electrical properties of the BGZO film.

Effect of Homo-buffer Layers on the Properties of Sputtering Deposited Ga2O3 Films

β- Ga2O3 films were grown by radio-frequency magnetron sputtering method. The influence of Ga2O3 buffer layers and annealing treatment on the structural, optical, morphological and electrical properties of Ga2O3 films was studied. The results revealed an improvement of crystalline quality and transmittance of annealed β- Ga2O3 films prepared with homo-buffer layers. Ga2O3 film UV photodetectors were fabricated with a new B and Ga co-doped ZnO films (BGZO)/Au interdigitated electrode. A good ohmic contact was formed between the film and the electrode. For the detector based on Ga2O3 films with buffer layers, a higher value of photo response and faster response times was obtained.

Optical and structural study of Ga and In co-doped ZnO films

Doping with different metals leads to effective modification of structural, morphological, optical, electrical and chemical properties of ZnO films. Ga and In co-doped ZnO thin films have been succesfully obtained by the sol-gel method, using spin coating. FTIR detailed studies of undoped ZnO, In or Ga doped and In-Ga- ZnO films reveal that Ga and In co-doping affects the shapes and the intensity of the absorption bands. No clear traces of Ga–O and In–O bonds are detected. XRD analysis shows that In and Ga co-doped ZnO films posses lower crystalization compared to ZnO and ZnO:Ga. Respectively, the crystallite sizes of co-doped systems are significantly smaller compared to ZnO crystallites and closed to that of ZnO:Ga 3 films. The lattice parameters, texture coefficients are determined from XRD data. Optical characterization shows that the In and Ga co-doped ZnO films are found to be less transparent compared to sol-gel derived ZnO and ZnO:Ga films. The optical band gaps of co-doped films are estimated as a function of the annealing temperatures, ranging from 3.41 up to 3.28eV. It has been observed that the optical band gap values of In-Ga-Zn-O films are strongly dependent on the indium doping concentration.

The effects of substrate temperature on properties of B and Ga co-doped ZnO thin films grown by RF magnetron sputtering

Abstract In this work, B and Ga co-doped ZnO (BGZO) films were fabricated by RF magnetron sputtering method. The effects of substrate temperature on the electrical, optical, structural and morphological properties of B and Ga co-doped ZnO films were investigated. XRD results revealed that deposited films were textured along c-axis and maintain wurtzite crystalline symmetry. As substrate temperature increased up to 200 °C, the film crystallinity was improved and the crystallite sizes became larger. At the substrate temperature of 200 °C, the films showed lower resistivity, higher Hall mobility and higher optical band gap. It was also observed that all films showed high transparency in the visible range (400–800 nm), which did not change obviously with the substrate temperature.

Effect of Sputtering Pressure on the Properties of Boron and Gallium Co-doped ZnO Thin Films

B and Ga co-doped ZnO films were fabricated by RF magnetron sputtering method. The effects of sputtering pressure on the electrical, optical, structural and morphological properties of the films (BGZO) were investigated. As sputtering pressure increased up to 6mTorr, the film crystallinity was improved. At the sputtering pressure of 6mTorr, the films showed smooth and dense of film surface, lower resistivity and higher Hall mobility. It was also observed that all films showed high transparency in the visible range. The film showed blue shift of optical band gap with increaseing of sputtering pressure.

The effects of thickness on properties of B and Ga co-doped ZnO films grown by magnetron sputtering

We investigated the effects of thickness on the electrical, optical, structural and morphological properties of B and Ga co-doped ZnO (BGZO) films grown by radio frequency (RF) magnetron sputtering. All the prepared BGZO films showed preferentially c-axis orientation and structure of hexagonal wurtzite. The results also indicated that with an increase in film thickness, the crystallite sizes of the films were increased and the optical band gap (Eg) was decreased. Below a critical thickness of about 210nm, the thickness of the BGZO films significantly affected the electrical properties of the films. The average transmittance for all the grown films did not change obviously with the thickness.

The effects of thickness on the electrical, optical, structural and morphological properties of Al and Ga co-doped ZnO films grown by linear facing target sputtering

We investigated the effects of thickness on the electrical, optical, structural, and morphological properties of Al and Ga co-doped ZnO films (AGZO) grown by linear facing target sputtering (LFTS) for use as a transparent contact layer (TCL) in GaN-light emitting diodes (LEDs). Below a critical thickness of 200 nm, the resistivity and optical transmittance of the AGZO films were significantly affected by the thickness of the AGZO films. However, above a thickness of 200 nm, the AGZO films had similar resistivities and optical transmittances due to the stable columnar structure, which developed at a thickness of 200 nm. Due to the change of the growth mode with increasing thickness, the microstructure and surface morphology were also affected by the film thickness. Based on the figure of merit values, we determined that the optimized thickness of the LFTS-grown AGZO film was 200 nm, which was applied in a GaN-LED as a TCL. Successful operation of GaN-LEDs with an optimized AGZO film without plasma damage indicates that the LFTS-grown AGZO film is promising plasma damage-free TCL for use in GaN-LEDs.

Co-Doped ZnO Transparent Conductive Films for LCD and UV Detectors

Zr,Ga co-doped ZnO transparent conductive films were deposited on glass substrates by DC magnetron sputtering at room temperature.The influence of sputtering pressure on the structural,electrical,and optical properties of Zr,Ga co-doped ZnO films was investigated by X-ray diffraction,scanning electron microscopy (SEM),digital four-point probe,and optical transmission spectroscopy.The lowest resistivity of the Zr,Ga co-doped ZnO film is 3.01×10-4Ω﹒cm.All the films present a high transmittance of above 91% in the visible range.These results make the possibility for liquid crystal display (LCD) and UV photoconductive detectors.

Co-Doped ZnO Transparent Conductive Films for LCD and UV Detectors

Zr,Ga co-doped ZnO transparent conductive films were deposited on glass substrates by DC magnetron sputtering at room temperature.The influence of sputtering pressure on the structural,electrical,and optical properties of Zr,Ga co-doped ZnO films was investigated by X-ray diffraction,scanning electron microscopy (SEM),digital four-point probe,and optical transmission spectroscopy.The lowest resistivity of the Zr,Ga co-doped ZnO film is 3.01×10-4Ω﹒cm.All the films present a high transmittance of above 91% in the visible range.These results make the possibility for liquid crystal display (LCD) and UV photoconductive detectors.

Investigation of electronic and optical properties in Al−Ga codoped ZnO thin films

Electronic and optical properties of Al−Ga codoped ZnO thin films were investigated by post-annealing. The lowest resistivity of the Al–Ga codoped ZnO films was observed from the 450 °C-annealed sample. The Fermi-level shift of the Al−Ga codoped ZnO film was ∼0.6 eV from x-ray photoelectron spectroscopy, and the widening of optical-bandgap in the Al−Ga codoped ZnO film was ∼0.3 eV. The correlations of optical-bandgap with Fermi-level shift and conduction band filling were suggested by schematic band diagrams.

(Ga,N) and (Cu,Ga) Co-Doped ZnO Films for Improving Photoelectrochemical Response for Solar Driven Hydrogen Production

In this study, Bandgap-reduced p-type ZnO thin films were synthesized through Cu and Ga co-doping. The ZnO:(Cu,Ga) films were synthesized by RF magnetron sputtering in O2 gas ambient at room temperature and then annealed at 500° in air for 2 hours. We found that the carrier concentration tuning does not significantly change the bandgap and crystallinity of the ZnO:Cu films. However, it can optimize the carrier concentration and thus dramatically enhance PEC response for the bandgap-reduced p-type ZnO thin films. The co-doped ZnO:(Ga,N) films were deposited by co-sputtering at room temperature, followed by post-annealing at 500°. We found that the ZnO:(Ga,N) films exhibited greatly enhanced crystallinity compared to ZnO:N films doped with pure N. Furthermore, the ZnO:(Ga,N) films showed much higher N-incorporation than ZnO:N films. As a result, the ZnO:(Ga,N) films showed significantly higher photocurrents than ZnO:N films.

(Ga,N) and (Cu,Ga) Co-Doped ZnO Films for Improving Photoelectrochemical Response for Solar Driven Hydrogen Production

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P-type ZnO thin films prepared by in situ oxidation of DC sputtered Zn3N2:Ga

The feasibility of a new fabrication route for N and Ga codoped p-type ZnO thin films on glass substrates, consisting of DC sputtering deposition of Zn3N2:Ga precursors followed by in situ oxidation in high purity oxygen, has been studied. The effects of oxidation temperature on the structural, optical and electrical properties of the samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical transmittance and Hall effect measurements. The results were compared to a control film without Ga. XRD analyses revealed that the Zn3N2 films entirely transformed into ZnO films after annealing Zn3N2 films in oxygen over 500 °C for 2 h. Hall effect measurements confirmed p-type conduction in N and Ga codoped ZnO films with a low resistivity of 19.8 Ω · cm, a high hole concentration of 4.6 × 1018 cm−3 and a Hall mobility of 0.7 cm2/(V·s). These results demonstrate a promising approach to fabricate low resistivity p-type ZnO with high hole concentration.

Structural and magnetic properties of Co–Ga co-doped ZnO thin films fabricated by pulsed laser deposition

Co–Ga co-doped ZnO films were fabricated by pulsed laser deposition on quartz substrates. The obtained films exhibited a wurtzite structure with c-axes growth preference. Optical measurements showed the presence of the cobalt ions in a tetrahedral crystal field, which proved that the Co ion substitution in the ZnO lattice, acting as magnetic cation. Hall measurements indicated that the films were n-type conductive with the electron concentrations of ~ 10 20/cm 3. This value was much higher than that of the Co-doped films, suggesting the effective incorporation of Ga in the films. Room temperature ferromagnetism was observed for the Ga–Co co-doped thin films.