In the upcoming information, digital, and multimedia age, light-emitting diodes (LEDs) based on wide-bandgap semiconductors have drawn much attention. The high efficiency, fast switching time, high color gamut, low power consumption, semipermanence, and low heat output of the LEDs have led to many new applications. The backlight units in liquid-crystal displays have been replaced by high-efficiency LEDs. As the efficiency of LEDs was further improved, many products equipped with LEDs have been reported. To meet the requirement of high-brightness LEDs for illumination, mobile appliances, automotive, and displays, it is necessary to develop new wide-bandgap semiconductors such as ZnO, which has excellent structural and physical properties compared to GaN.
Zinc oxide (ZnO) is a II-VI compound semiconductor with a hexagonal wurtzite structure. Recently, ZnO has attracted much attention for its application in various fields such as UV light-emitting devices, varistors, transparent high power electronics, optical waveguides and solar cells. In particular, ZnO has been considered as promising materials for short-wavelength optoelectronic devices because it has a direct bandgap of 3.3 eV and a low threshold voltage. ZnO also has a number of advantages over GaN, the wide-bandgap semiconductor currently utilized in the short-wavelength optoelectronics industry. Some of these advantages include a large exciton binding energy (~ 60 meV), a higher radiation hardness, simplified processing due to amenability to conventional chemical wet etching and the availability of large area substrates at relatively low material costs.
It has been compelling research attention for a long time because of its applications in many scientific and industrial areas such as piezoelectric transducers, optical waveguides, acousto-optic media, conductive gas sensors, transparent conductive electrodes, and varistors. It has now received increasing attention and is recognized as a promising candidate for applications related to its optoelectronic possibilities in the UV range. Furthermore, its piezoelectric properties could allow the development of SAW filters to be integrated in future analog circuits for portable electronics for which there is a strong need.
ZnO nanostructure can be easily produced by several growth techniques because ZnO have the preferred c-axis orientation due to the minimal surface energy in the ZnO wurtzite structure. The 1 dimensional (1D) ZnO nanostructures which include highly ordered nanowire arrays, nanorods, and nanobelts are promising candidates for nano-electronic and photonic. 1D ZnO nanostructures are found to be highly suitable for nanoscale applications such as room temperature laser, field effect transistor, nanoresonator, etc.