KEYWORDS: Thin films, Zinc oxide, Antimony, Thin film growth, Temperature metrology, Annealing, Gallium nitride, Zinc, Pulsed laser deposition, Chemical elements
We present the effect of post-annealing on the p-type ZnO:Sb thin film. The ZnO:Sb thin films were grown by pulsed
laser deposition (PLD) method. Undoped ZnO thin film was inserted between the ZnO:Sb thin films and GaN
template/sapphire substrate to reduce lattice mismatch. The ZnO:Sb thin films grown in the temperature range of 400 °C and 800 °C were all n-type in the as-grown state. However, when post-annealing was performed the film grown at
600 °C and annealed at 700 °C for 60 min showed p-type conductivity with a hole concentration of 1.4 x 1017 cm-3 and a
reasonable mobility of 6.7 cm2/Vs. The annealed ZnO:Sb thin film grown at a relatively low temperature of 400 °C was
highly resistive with a resistivity of 1.95 x 105 Ωcm. This was perhaps due to the low incorporation of Sb in the film.
ZnO:Sb thin film grown at a relatively high temperature of 800 °C showed n-type conductivity even after annealing, and
the carrier concentration only dropped from 1.32 x 1017 cm-3 of the as-grown state to 3.08 x 1015 cm-3 after annealing.
This may have been due to the formation of Sb compound in ZnO inhibiting the activation of Sb during post-annealing.
Therefore, post-annealing of ZnO:Sb grown at adequate temperature is crucial to obtain p-type ZnO thin film.
ZnO thin film growth and ZnO nanorods growth on a Si (100) substrate through a two-step, off-axis pulsed laser
deposition (PLD) are reported. ZnO morphologies were measured and the post-annealed ZnO films grown at Tg = 700 °C
had very smooth surfaces and the rms roughness was about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted
between ZnO epi-layer and GaN/sapphire substrates. It was confirmed by cathode luminescence (CL) spectrum that the
ZnO film grown at 700 °C had very low visible luminescence, which means a decrease of the deep level defects. In the
case of ZnO nanorods, controlling growth parameters during deposition enabled to adjust the dimensions of nanorods.
The diameters of the grown nanorods ranged from 50 to 700 nm and the lengths are from 2 to 10 μm. The CL spectra
were used to evaluate the states of defects within the ZnO nanorods. According to the CL results, the thinnest nanorod
arrays were found to have fewer defects, while more defects were inserted as nanorods became thicker.
This paper describes two topics. (1): Nano-processing by near-field optics can fabricate nano-scale structures even with
near-infrared 800 nmTi:saphire laser. New phenomena using particles, leading to a new nano-processing technique via
plasmonics, even with the use of dielectric particles is reported. The physics of nano-hole fabrication process is
switchable simply by the laser fluence. (2): ZnO nanorod arrays on Si (100) substrate were grown by pulsed laser
deposition (PLD) method, and then coated with Au. Two samples of Au-coated nanorod arrays with different average
diameters of 150 nm and 400 nm were prepared to investigate the size dependence of the surface enhanced Raman
scattering (SERS). The diameter of the nanorods was well controllable by the substrate position during PLD. High SERS
enhancement was observed from both Au-coated ZnO nanorod arrays. The Raman spectra of Rhodamine 6G (R6G) as
low as 1 nM were measured with average diameter of 400 nm at an excitation wavelength of 532 nm.
We investigate post-annealing effects using an epi-GaN substrates for ZnO thin film growth by pulsed laser deposition
(PLD). The growth of ZnO nanorods on a Si(100) substrate through a two-step process, annealing and off-axis PLD,
without a metal catalyst is demonstrated as well. The as-grown films were annealed for one hour under atmospheric
pressure air. ZnO morphologies after annealing were measured and the post-annealed ZnO films grown at Tg= 700oC
had very smooth surfaces and the rms roughness was about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted
between ZnO epi-layer and GaN/sapphire substrates. It was evident by AFM that growth temperature of 700oC helps the
films grow in a step-flow growth mode. It was confirmed by cathode luminescence (CL) spectrum that the ZnO film
grown at 700oC had very low visible luminescence, resulting in a decrease of the deep level defects. In the case of ZnO
nanorods, controlling growth parameters during deposition enabled the adjustment of the dimensions of nanorods. The
diameters of the grown nanorods ranged from 50 to 700 nm and the lengths are from 2 to 10 μm. The CL spectra were
used to evaluate the states of defects within the ZnO nanorods. According to the CL results, the thinnest nanorod arrays
were found to have fewer defects, while more defects were introduced as nanorods became thicker.
The ZnO nanorod possesses large surface area, high aspect ratio and quantum confinement effect. Therefore,
the ZnO nanorod would be a candidate for a gas sensor, dye-sensitized solar cell, etc. For device applications, it is very
important to control the growth of ZnO nanorods. Pulsed-laser deposition (PLD) is an effective method to grow ZnO
nanostructures. In this paper, we have fabricated the ZnO nanorods on Si substrate through a two-step process without a
metal catalyst. As for a first step, ZnO powder dispersed on Si substrate is thermally annealed in order to fabricate ZnO
seed layer. The seed acts as a catalyst of the ZnO nanorod growth, and is found to be zinc silicate (112) by XRD
measurement. Secondly, ZnO is deposited on the seed layer by PLD at an argon pressure of 10-2 Torr. The length of
nanorods is up to 4 μm with a typical diameter of 100 nm. The CL emission spectra are observed and the existence of
defects within the ZnO nanorods has been identified. By controlling the growth parameters, high-quality nanorods
without defects were fabricated by this two-step PLD method.
We demonstrate the effect of N-doping in various phases, where N-doped states, bandgap shifts, and photocatalytic efficiencies are determined. The N-doped TiO2 films were grown by pulsed-laser deposition using TiON targets. The crystal structures were analyzed using x-ray diffraction and Raman spectroscopy. The crystalline phases of TiO2 were artificially controlled by choosing appropriate substrates. The anatase and rutile were epitaxially grown on (100) LaAlO3 and (001) sapphire substrates. Rutile-anatase mixtured phase were grown on soda lime glass substrates. We here note that N-concentration strongly depends on the growth temperature, so that we kept the growth temperature at 300 °C in order to fix the N concentrations for respective specimens. Chemical bonding states of N within the matrix were investigated by x-ray photoelectron spectroscopy. The optical absorption and bandgap were measured using UV-VIS spectrometer. The photocatalytic activity of the films was evaluted by measuring the decompositon rate of methylene blue solution with the visible light illumination.
Among the well-known photo-catalytic materials, the anatase TiO2 is the most promising in terms of its chemical stability and high reactivity. It is known that the photo-catalytic activity under the visible light irradiation can be enhanced by nitrogen doping into the anatase, because the substitutional nitrogen produces an impurity state which absorbs the visible light. In this paper, we will report on the properties of the nitrogen doped films with different dopant concentrations. The anatase films are prepared by KrF excimer pulsed-laser ablation of TiO2-xNx targets. The films are deposited on the (100) LaAlO3 substrate which has a good lattice matching with anatase (~ 0.2%). First, we discuss the optimization of the growth conditions. To prepare the nitrogen doped anatase thin films, we have developed a low-temperature epitaxy. The growth of anatase-type TiO2 was confirmed using an x-ray diffraction (XRD). The nitrogen incorporation was evaluated by an x-ray photoemission spectroscopy (XPS). The as-grown films have very smooth surface and exhibit good amphiphilic properties. Then, we present the photo-catalytic activity of the films. The nitrogen doping concentration was varied by adjusting the amount of nitrogen in the ablation targets. The photo-catalytic activity was measured by the decomposition rate of methylene blue solution under a fluorescent light illumination.
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