Study on the Effect of Mg Dopant on the Properties of ZnO Thin Film Prepared by Sol Gel

Abstract

Thin film technology is the field of thin film deposition process and it is linked to nanotechnology. Thin film technology has been applied in many fields. Mostly thin film is used in electronic components and electronic displays such as LED displays and lighting, thin film solar cell. Semiconducting material, insulating materials or metal silicide conductors are typically made up of these thin films. Doping is one of the methods to change the properties of thin film. There various types of materials could be used as doping element. Different types of element has different properties which will cause properties of ZnO thin film to be changed. Thin film of ZnO could change from semiconductor to insulator or conductor depends on types doping element. However, doping using Mg mostly will changed the band gap of thin film. , ZnO is chosen as semiconducting material since it is transparent conducting oxide. At room temperature, it has wide direct band gap with value of 3.37eV that in group II-IV semiconductor. Due to luminescence in visible and near UV range of spectrum, it is widely used in sensors, light emitting diodes or solar cells. The doping element being chosen is Mg because the similarity in ionic radius between Mg and Zn. After thin film of ZnO is doped with Mg, several properties of ZnO thin film is changed. The research shows that the surface of undoped ZnO thin film will contain much void and uniform grain size. However, the surface thin film that doped with Mg is dense and uniform while the void will decreases with concentration of Mg. This shows that there is improved in surface morphology. Sol gel techniques had many advantages compared to other method. Sol gel method requires low sintering temperature (200˚C to 600˚C). It is an economical method as it is low cost and it can be carried out using simple and inexpensive equipment. Sol gel method has the ability to change microstructure of film by changing the pH, temperature and viscosity of sol. This thesis discuss about the sol gel spin coating techniques to produce Mg doped ZnO thin films. Zinc acetate dehydrate, absolute ethanol and diethanolamine used as sol gel precursor while magnesium chloride as source of doping element. Sol gel was coated onto glass slides that wrapped with aluminium foil using spin coated instruments. After that, the thin film was annealing at 400˚C for one hour. The thin films with varying concentration of Mg and spin speed is characterized using XRD, FESEM, PL, UV-Vis and four point probes. Thin films that fabricated with 5 wt% Mg and spin speed of 2000 rpm has better result in term of characterization of XRD and FESEM among all Mg doped ZnO thin films since it has more crystal growth of MgO and it has the best surface morphology with uniform nanoparticles structure eventhough it has moderate transparency and energy band gap. Furthermore, the resistivity of this samples is also higher compared to sample with 5 wt% and 3000 rpm but lower than sample with 10 wt% and 2000 rpm. Sample with 10 wt% and 2000 rpm has the best results among all sample in application pf photonic since the intensity peaks of PL is the highest.