Recent development in the growth of ZnO nanoparticles thin film by magnetron sputtering.

Zinc oxide (ZnO) nanoparticles is an attractive candidate and gain attention for their novel properties and promising applications such as optoelectronic devices by virtue of their high surface to volume ratio and molecular absorption and desorption characteristics. Ultraviolet light emmiters, gas sensor (particularly for hydrogen) etc. are some of the potential applications of this wide direct band gap (E_g ~ 3.37 eV) semiconductor. Currently, there are considerable amount of research attention on the growth of p-type ZnO thin film and nanoparticles. Thus, in this paper we will discuss recent development in the growth of p-type and ZnO thin film in nanoparticles by magnetron sputtering. There are several important parameters (e.g. RF power/DC voltage, working pressure, substrates temperature and target to substrates distance) that we have to consider in order to attain small grain size (<100 nm). Grain size that are peculiarly small can be achieved by reducing kinetic energy of the sputtered material and lowering the growth rates either by increasing the working pressure or reducing RF power/ DC voltage. The temperature of the substrate is also believed to have some influence in slowing the kinetic energy of the sputtered atoms. For ZnO, n- type conductivity is easy to realize via excess zinc or with trivalent dopants such as Aluminium (Al), Gallium (Ga) or Indium (In) by substituting Zn²⁺ ions with Al³⁺ ions. Meanwhile, p-type doping has recently been achieved by doping with the group V elements. Most of the attempts have employed Nitrogen (N) as the acceptor to substitute Oxygen (O) by introducing either Nitrous Oxide (N₂O), Nitric Oxide (NO), Ammonia (NH₃) or Nitrogen (N₂) gas. Other elements of group V are Phosphorus (P), Arsenic (As) and Antimony (Sb). Recently, Phosphorus oxide (P₂O₅) has been doped in ZnO thin film and post deposition of rapid thermal annealing (RTA) h- - as been used to activate the dopants. Furthermore, a new method called codoping has been proposed to produce p-type ZnO, which was achieved using acceptors and reactive donors simultaneously to increase the solubility of Nitrogen in ZnO.