DETERMINATION OF THE BAND-GAP ENERGY OF CERAMIC ZnO DOPED WITH MnO BY PHOTOPYROELECTRIC TECHNIQUE

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°C to 1300°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 vs h and is about 3.0 eV for samples with 850°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 diffractometry 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 ZnMn₂O₄ only at 1050°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.