Solid State Science and Technology, Vol. 13, No 1 & 2 (2005) 226-233 ISSN 0128-7389 226 DETERMINATION OF THE BAND-GAP ENERGY OF CERAMIC ZnO DOPED WITH MnO BY PHOTOPYROELECTRIC TECHNIQUE Azmi Zakaria, Zahid Rizwan, Mansor Hashim, Abdul Halim Shaari, W. Mohmood Mat Yunus, Elias Saion. Department of Physics, Faculty of Science, Universiti Putra Malaysia 43400 Serdang, Selangor. E-mail: azmizak@fsas.upm.edu.my ABSTRACT Photopyroelectric spectroscopy (PPES) is used to study the band-gap energy (E g ) of ZnO doped with MnO of 0.1 to 2.0 Mol % and sintered at various isothermal sintering temperature ranged from 850 o C to 1300 o C. The wavelength of incident light is kept in the range from 300 nm to 800 nm at a modulation frequency of 9 Hz. The photopyroelectric spectrum with reference to the doping level and sintering temperature is discussed. E g is estimated from the plot ( ) 2 ν ρh vs hν and is about 3.0 eV for samples with 850 o C sintering temperature at all doping levels. At higher sintering temperatures the value of E g decreases with the MnO mol %; beyond 1 mol % E g becomes constant at about 2.0 eV. The x-ray diffractrometry shows that the crystal structure of ZnO doped with different mol % of MnO at all sintering temperatures remains to be of hexagonal type but a small peak is found related to the new phase ZnMn 2 O 4 only at 1050 o C sintering temperature at 2 mol % of MnO doping level. Density is decreased from 95.5% to 87% with the increase in sintering temperature and doping level. INTRODUCTION The ZnO based ceramic semiconductors are widely used as gas sensors (Lin et al, 1998), piezoelectrics, electrodes for solar cells, phosphors, transparent conducting films (Look, 2001), and varistors. Varistors possess high energy absorption capability against various surges. They are extensively used as protective devices to regulate transient voltage surges (Choon, 2003) of unwanted magnitudes which refer to the damaging voltage transients that exceed more than 10% of the operating voltage of the equipments being protected. ZnO based varistors have super-fast response to over-voltage transients as they sense and clamp transients in nano-second speed, repeatedly in thousands of times without being destroyed (David,1999). They can perform surge-suppressing functions equally in both polarities even in ac and dc circuits over a wide range of voltages. They have high energy-absorption capability with energy density up to 300 J/cm 3 with low power loss of only 10-100 mW/cm 3 with long life spans under hostile