Sol - Gel Prepared Zno Thin Films

Zinc oxide (ZnO) as a wide band-gap (3.3eV) compound semiconductor with wurtzite crystal structure, is gaining importance for the possible application as a semiconductor laser, due to its high exciton binding energy of 60 meV. Al-doped ZnO (AZO) thin films are emerging as an alternative potential candidate for ITO (Sn-doped In₂O₃) flims recently not only because of their comparable optical and electrical properties to ITO films, but also because of their higher thermal and chemical stability under the exposure to hydrogen plasma than ITO. There are many techniques used to deposition ZnO thin films, such as sputtering, chemical vapor deposition (CVD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE) and so on. However, from a practical standpoint, these processes have the disadvantage of the need for vacuum apparatus. Yet, the sol-gel method not only has voided the disadvantage, but also has the potential for preparation of films of large area and complicated forms on various substrates. In this work, ZnO thin films were prepared by sol-gel method on the glass and silicon substrates in order to study the influence of the process conditions on the crystallization, orientation and morphology of the films. Then the films with the optimum properties were obtained by improving the process conditions. The relations between the structure of the Al-doped ZnO thin films and resistivity and transmittivity were found. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) and ultraviolet-visible (UV-vis) spectrum were used to characterize the crystallization behavior, orientation and surface morphology of the ZnO thin films. It is revealed that the pre-treatment temperature is significant to the c-axis orientation and the optimal temperature is 300℃. The relations between the sol concentration, post-treatment temperature, the thickness of the films and orientation and transmittivity were researched. Four point resistivity test system and ultraviolet-visible (UV-vis) spectrumeter were used to measure the electrical and optical properties of the Al-doped ZnO thin films. The results suggest that at higher pre-treatment temperatures the resistivity is high, as...