**7. ZnO nanorods based devices**

ZnO based nanorods have received a good interest in various optoelectronic nanoscale devices. These devices include the photovoltaic cells, UV laser diodes [46], LEDs, optical sensors, and UV photodetectors [47]. Several applications based on ZnO require a large surface area. The simplest method to increase the surface of the ZnO layer is by growing nanorods. The larger the surface area the more photons are expected to be absorbed by ZnO layer [48]. One way to improve the crystalline structure and the photoluminescence spectra of ZnO nanorods is by annealing process [48].

The ZnO nanorods are being fabricated using several methods. These fabrication methods include the hydrothermal method [49], metal oxide chemical vapor deposition method [50], pulsed laser deposition method [51], aqueous solution method [52]. In these methods, the surface morphologies, optical and electrical properties of ZnO nanorods are depending on the fabrication parameters. These parameters include the deposition time, temperature, and post deposition annealing. The ZnO nanorods are shown in **Figure 4**.

Other fabrication methods of the ZnO nanoshape films are including the sol-gel technique, RF magnetron sputtering, electron beam evaporation, spray pyrolysis (SP), and molecular beam epitaxy, electrochemical deposition [54]. The electrochemical deposition wet method is a well-established solution based process to obtain ZnO nanoshapes thin films [55]. It has many advantages including the low cost and the temperature deposition over other types of fabrication.

**Figure 4.** *ZnO nanorods [53].*
