Browsing by Author "MUHAMMAD ASAD ALI"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Deposition of ZnO thin films by thermal evaporator
    (UMT, Lahore, 2015) MUHAMMAD ASAD ALI
    The ZnO films are deposited on glass substrate in oxygen environment by thermal evaporator for various applied voltages (130 V, 140 V and 150 V) while the constant parameters are: (i) source to substrate distance (0.5 cm), (ii) oxygen pressure (1 mbar) and deposition time (2 hours). The deposition of ZnO films by thermal evaporator is done through evaporation of Zn and transportation of involved species (Zn and O). The deposition rate of ZnO film strongly depends on oxygen pressure. The temperature of thermal evaporator plate (TEP) is found to be 420C at 130 AV which increases with the increase of applied voltage (AV). The deposited ZnO films are characterized by using XRD, SEM and SE techniques. XRD patterns reveal the development of diffraction peak related to ZnO (100) plane when deposited for different temperatures of thermal evaporator plate (TEP). The crystallinity of ZnO (100) plane is increased with the increase of temperature in TEP. The crystallite size, dislocation density and residual stresses developed in ZnO (100) plane are associated with the increase of temperature of TEP. SEM analysis demonstrates the formation of tree like microstructure of nano-particles. However, the microstructures of nano-particles are of different shapes like (nano-rod, nano-fiber, nano-canal and micro-rock) whereas the size of the nano-structures of rod, fiber is associated with the increase of temperature of TEP. Careful investigation reveals that a compact and uniform film that comprises of different shaped nano-structures is formed behind the upper layer of ZnO films. The changes in micro-structural features are associated with the increase of temperature of thermal evaporator plate. SE analysis shows the refractive index and thickness of ZnO films grown for different temperatures of TEP. The maximum optical energy band gap of ZnO film is found to be 2.1 eV for 420C temperature of TEP. The energy band gap is further decrease with the increase of temperature of TEP. Interestingly, the calculated value of energy band gap of ZnO film is smaller than its reported value. The decrease in energy band gap of ZnO films may be due to: (i) increase in crystallinity of ZnO films deposited for higher temperature and (ii) diffusion of oxygen species (as impurity) of different energy creating more micro-strains and defects (iii) low concentration of oxygen species.