I–V performances of aligned ZnO nanorods/Mg0.3Zn0.7O thin film heterojunction for MESFET applications

Abstract

Zinc oxide (ZnO) is a promising candidates for electronics devices applications due to its unique properties that being extensively explored nowadays. Having a large bandgap of 3.4 eV at room temperature and large exciton binding energy of 60 meV [1] has made ZnO to become transparent to visible light. MgZnO also transparent to visible light where the bandgap can be tailored to reach almost 4.6 eV [2]. By introducing these two transparent materials in MESFET applications, such transistor could be particularly useful in display technologies as the transistor will no longer block the light. Mg0.3Zn0.7O with the resistance of 106 Ω/cm [3], can acts as a semi-insulating material in MESFET structure, was deposited on quartz substrate before being immersed in ZnO solution for 4.5 hours. The ZnO solution of 0.05M was prepared one day earlier, was stirred and heat, before being left at room temperature to get better solubility. This chemical bath deposition technique was believed to be very easy, low cost technique, yet can produced a very uniform, aligned ZnO nanorods. Field emission scanning electron microscope (FESEM) depicts that an aligned ZnO nanorods were successfully grown as in Fig. 1 on Mg0.3Zn0.7O that in the other way has acted as a catalyst for the better growth of aligned ZnO. The diameter of the nanorod has found out to be in the average of 75 nm while the thickness is around 1.6 µm. X-ray diffraction spectra has recorded that this aligned ZnO shows very intense (002) peak, which was between 15° and 60°, indicating a high degree of crystallinity. Keithley measurement system has been employed to study the IV response of this heterojunction of ZnO/Mg0.3Zn0.7O. It is well understood that different metal used as a contact will resulted in a different behavior of IV responses. Due to that, 4 different metals has been used to study the IV responses. For the metallization purposed, electron beam evaporator has been employed to deposit aluminum, gold, platinum and nickel as a metal contact. It shows that these 4 selected metals gave different behavior of IV responses due to different work function of each metal. To study the performance of aligned ZnO/Mg0.3Zn0.7O heterostructures, the IV response of thin film ZnO, thin film ZnO/Mg0.3Zn0.7O, and thin film Mg0.3Zn0.7O has been taken as a reference. It obviously revealed that aligned ZnO/Mg0.3Zn0.7O heterostructures gave better performance of IV responses compared to others which will be discussed further in this paper. It is suggested that this heterostructures can be used in MESFET applications due to its simplicity in fabrication and the IV performance that suitable for the use of transparent transistor in display technologies.