Effects of growth temperature on structural properties of ZnO thin films
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Effects of growth temperature on structural properties of ZnO thin films Kwang-Sik Kim, Jung-Ho Lee and Hyoun-Woo Kim School of Materials Science and Engineering, In-ha University, #253, Yonghyun-Dong, Nam-Gu, Incheon 402-751, Korea. ABSTRACT Highly-oriented ZnO thin films have been successfully deposited on (100)Si by metal 400 . We report on the structural organic chemical vapor deposition (MOCVD) at 250 properties of ZnO thin film at various temperatures. The crystallinity of thin films improved and the surface smoothness decreased with increasing growth temperature. In x-ray reflection analysis with respect to ZnO (0002) peak, the full width at half maximum (FWHM) of 0.4 was achieved at 400 .
℃∼ ℃
°
℃
INTRODUCTION ZnO has rapidly emerged as a promising optoelectronical material due to its large band gap of 3.37eV, low power threshold for optical pumping at room temperature (RT), and highly efficient UV emission resulted from a large exciton binding energy of 60 meV. Various deposition techniques, including sputtering [1], pulsed laser deposition (PLD)[2,3], chemical vapor deposition (CVD)[4,5], atomic layer deposition (ALD)[6], spray pyrolysis[7], metalorganic chemical vapor deposition (MOCVD)[8], and also molecular beam epitaxy(MBE)[9] have been employed for the growth of ZnO films. ZnO is also widely used in surface acoustic wave device and sensors. Because structural properties strongly affect the performance of a device, it is important to improve the quality of ZnO films. Most researchers grow ZnO films on sapphire substrates. We use silicon as a substrate to deposit ZnO film because it is more useful for optical-electronic integration in the future. We reveal that the ZnO films deposited on Si (100) substrates by MOCVD using diethylzinc (DEZ) and O2 can generate stronger emission in spite of lattice-mismatch between ZnO and Si. The structure and photoluminescence (PL) properties of the ZnO films depend on the growth temperature. We investigate the surface texture, morphology, crystal-orientation and film composition and reveal a relationship between crystallinity and surface smoothness of ZnO thin films. EXPERIMENTAL DETAILS The ZnO films were deposited on p-type (100) Si substrates (20 mm × 20 mm) by MOCVD system using Zn(C2H5)2 (99.9999% purity DEZ (Diethylzinc)) and O2 (99.999% purity). The DEZ was carried by Ar (99.999% purity) gas. Fig. 1 shows a schematic diagram of the MOCVD reactor used in our experiments. The deposition condition of each samples are listed in Table 1. Table 1. Growth condition in our experiments Temp 250
℃
Ar : O2 = 2 : 1
Sample A
300
℃
Sample B
400
℃
Sample C
K7.16.1 Downloaded from https:/www.cambridge.org/core. Columbia University Libraries, on 09 Jun 2017 at 06:03:23, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-722-K7.16
Figure 1. Schematic diagram of MOCVD system
λ
The crystal structures were characterized by x-ray diffraction (XRD: CuKa1 =1.5405). The surface morphology of ZnO fi
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