Disini saya membuat tulisan singkat tentang riset yang sedang saya lakukan. Just for practise :-)
ZnO has long been used in many applications such as food additive, cream to protect sunburn, rubber manufacturer, etc. Even though, ZnO has considered as semiconductor. The semicoconductor properties of ZnO have been studied since a long time ago. Based on semiconductor properties ZnO also has many wide applications such as piezoelectric transducers, optical waveguides, acoustic optic media, conductive gas sensors, transparent conductive electrodes, and varistor.
Nowadays ZnO has become promising candidate for application related to optoelectronics devices. These potential applications have improved research related to the growth of high quality ZnO thin films by a lot of different techniques, such as chemical vapour deposition (CVD), vapour phase transport (VPT), sputtering, molecular beam epitaxy (MBE), pulsed laser deposition (PLD), metal organic chemical vapor deposition (MOCVD), etc. Among of theses, Sputtering, PLD, MBE, and MOCVD are the most common in used for producing thin film and structure.
Instead of ZnO has simpler technology to growth the crystal and very unique properties for optoelectronic applications with the wide band gap (3.37eV) and large exciton binding energy (60 meV). It was also expected low cost production compared to GaN (GaN is one of III-V semiconductor common used in optoelectronic applications). However, ZnO is n type semiconductor which is hard be doped to become p type. This property called asymmetric properties semiconductor. In order to realize p type ZnO, various growth techniques and various dopant elements (N, P, As, etc) was reported in paper. Some of papers claimed have produced p type ZnO. Indeed, some of researchers doubt that p type of ZnO really stable.
In order to overcome this problem and to control the material properties, a clear understanding of physical processes (epitaxial growth, deposition, sputtering, etc) in ZnO is needed. It is useful in addition to obtaining low n-type background and realizes p type semiconductor of ZnO. In spite of many decades of investigations, some of the basic properties of ZnO still remain unclear. For example, the nature of the residual n-type conductivity in undoped ZnO films, whether being due to impurities of some native defect or defects, is still debatable. Some authors assign the residual background to intrinsic defects oxygen vacancies and interstitial zinc atoms, and others to non-controllable hydrogen impurities introduced during growth.