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.
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.
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