Free Exciton Luminescence Of Zno : Zn Microcrystals Under Electron Beam Excitation

Cathodoluminescence in a ZnO:Zn microparticle has been investigated at room temperature. The luminescence band in the ultraviolet region is attributed to the recombination of free exciton (FE) which is hardly observed under photoexcitation due to the band bending near the particle surface due to ionized oxygen vacancies. The intensity of FE luminescence becomes large in high accelerating voltage where the penetration depth of injected electrons exceeds the width of depletion layer. The band bending is found to be reduced by means of direct injection of electrons to the oxygen vacancies near the surface, and the intensity of FE luminescence increases nonlinearly with the beam current due to the improvement of recombination efficiency by the reduction of surface electric field. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.