Journal of the Korean Physical Society, Vol. 60, No. 10, May 2012, pp. 1539∼1542 Growth of ZnO and ZnMgO Nanorods on Si Substrates by Using Ultrasonic Spray Pyrolysis Hai Dong Nguyen, Rina Pandey, Shavkat Yuldashev, ∗ Dong Jin Lee and Tae Won Kang † Department of Physics, Dongguk University, Seoul 100-715, Korea (Received 4 July 2011, in final form 19 December 2011) We demonstrate the growth of ZnO and ZnMgO nanorods on Si substrates through a two-step process without a catalyst by using a simple ultrasonic spray pyrolysis method. First, a ZnO thin film was deposited on a Si substrate to make a seed layer; then, ZnO and ZnMgO nanorods were deposited on that seed layer. ZnO and ZnMgO nanorods with a p-n junction were obtained by using nitrogen doping for p-type nanorods, and gallium doping for n-type nanorods. A distinct electroluminescence was observed at room temperature from the ZnO and the ZnMgO nanorod structures under forward bias conditions. PACS numbers: 81.10.Bc, 61.46.Km, 78.55.Et Keywords: ZnO and ZnMgO nanorods, Ultrasonic spray pyrolysis, Luminescence DOI: 10.3938/jkps.60.1539 I. INTRODUCTION ZnO nanorods are the most promising nanostructures because of their large surface area, high aspect ratio, and unique shape. A large surface area is important for high-sensitivity sensors for gas detection. The high as- pect ratio of ZnO nanorods allows excellent field emis- sion for a high-efficiency electron source. More recently, ZnO nanorods have provided possibilities for valuable applications, such as light emitting diodes (LEDs) and solar cells, owing to their structural advantages over thin films [1,2]. For the realization of light-emitting devices operating in a wider wavelength region, the band gap of ZnO can be increased by Mg doping [3,4]. The ZnMgO alloy is also an important material for constructing het- erojunctions or superlattices to obtain high-performance light-emitting devices [5–9]. Ultrasonic spray pyrolysis is a method in which a nanostructure is deposited by spraying a solution with an ultrasonic nebulizer onto a heated surface, where the constituents react to form a desired chemical compound. In comparison with conventional methods, the ultrasonic spray pyrolysis method provides advantages such as low equipment cost, good thickness uniformity over a large area, low-temperature, and low-vacuum requirements in processing, and so forth. ZnO thin films grown on Si substrates by using ultrasonic spray pyrolysis have been reported [10], as has the growth of ZnO nanorods by using ultrasonic spray chemical vapor deposition with a * On leave from the Department of Thermophysics, Academy of Sciences of Uzbekistan † E-mail: twkang@dongguk.edu Au catalyst [11]. However, metal catalysts can remain as contaminants within nanorods and can produce un- desirable defects. Thus, a catalyst-free growth process is desired. Realizing size control is also desired for evalu- ating the size dependence of defects in nanorods and for various potential applications. In this paper, we report the growth of ZnO and Zn- MgO nanorods on Si substrates by using catalyst-free ultrasonic spray pyrolysis. The ZnO and the ZnMgO nanorods with a p-type conductivity were also obtained by using nitrogen doping. II. EXPERIMENT We employ an ultrasonic nebulizer with a frequency of 2.5 MHz for atomization of a solution. The high fre- quency of the ultrasonic source produces small droplets of the spraying solution with a uniform distribution. The geometry of the atomization chamber balances the grav- itational force in such a way that large droplets cannot be transported by the carrier gas into the growth cham- ber. The small precursor droplets are decomposed in the growth chamber before they reach the hot substrate sur- face, and the deposition occurs from the vapor phase. These growth conditions are similar to those of chemical vapor deposition (CVD). In order to prepare ZnO and ZnMgO nanorods, we used zinc acetate and magnesium acetate as the zinc and the magnesium sources, respectively. De-ionized water was used as a solvent, and oxygen gas as a carrier gas. n and p-type Si wafers were used as substrates for the -1539-