Low temperature growth of ZnO thin film on Si(100) substrates by metal organic chemical vapor deposition

Abstract

In recent years, wide band-gap semiconductor materials have attracted a great deal of attention for use in blue light-emitting and short-wavelength diodes. Additionally, due to its high conductance, chemical and thermal stability, and high piezoelectric coupling coefficient, ZnO is also used for piezoelectric devices, such as surface acoustic wave (SAW) devices [1] and bulk acoustic devices [2]. Various deposition techniques, including sputtering [3, 4], pulsed laser deposition (PLD) [5, 6], ion beam deposition [7], chemical vapor deposition (CVD) [8, 9], atomic layer deposition (ALD) [10], metal-organic chemical vapor deposition (MOCVD) [11, 12], and molecular beam epitaxy (MBE) [13] have been employed for the growth of ZnO films. However, MOCVD has an advantage in achieving devices in commercial level since high deposition rate and highquality film is attainable, especially at low pressure. High quality ZnO films grown on Si substrate pave the way from integration of devices with Si IC technology. Also, amorphous substrates such as SiO2 and glass substrate have obvious technological advantages and potential applications [14]. Although most researchers have grown ZnO films on sapphire substrates, there are not many reports on growing ZnO thin films on Si or Sibased materials by MOCVD technique. Furthermore, there are rare reports on the MOCVD growth of ZnO at low temperatures below 300 ◦C. In this work, we investigate the growth of ZnO thin films on silicon substrate at the temperature range of 100–200 ◦C by employing the MOCVD technique. Since the material properties strongly affect the performance of a device, the influence of substrate temperature on the structural properties of the samples are presented. The ZnO films were deposited on p-type Si(100) substrates by MOCVD system using Zn(C2H5)2 (99.9999% purity DEZn (diethylzinc)) and O2 (99.999% purity). Fig. 1 shows a schematic diagram of the MOCVD reactor used in our experiments. Before loading into the reactor, the substrate was cleaned in acetone for 10 min, HF (20:1) for 1 min and then rinsed by deionized water for 1 min. High-purity Ar was passed through the DEZn bubbler and saturated with DEZn vapor to the reactor. For MOCVD growth of ZnO films, the gas phase reaction will result in particle formation, which will degrade the ZnO film quality. In order to minimize the gas phase reaction, Zn(C2H5)2