Study Of Optical Polarization And Photoluminescence Enhancement Of ZnMgO Films

As a novel II-VI direct band gap semiconductor material,Zno has large bandgap and high exciton binding energy,making it a potential candidate for electronic and optoelectronic devices,such as light emitting diode(LEDs),laser diode(LDs),UV detector and thin film transistors.In the past several decades,great peogress has been made in energy band engineering and optical properties of ZnO-based materials.At present,the research on ZnO-based materilas is mainly concentrated in the ZnMgO materials.However,the study of anisotropic optical properties is still lacking and the optical properties of ZnMgO need to be improved.Under this ground,we have studied the optical properties of ZnMgO films,mainly the optical anisotropic characteristic of nonpolar a-plane Zn1-xMgxO films and the photoluminesce enhancement of ZnMgO films by hydrogen plasma treatment.The main achievements are as follows:(1)Polarized Raman measurement and Polarized PL measurement are carried out to obtain the anisotropic strains and the degree of polarization of photo luminescence(p)in nonploar a-plane Zn1-xMgxO(x=0.01,0.03,0.1)films.Large p approximate to 1 is obtained in each nonpolar a-plane Zn1-xMgxO films,which is higher than the results of previous research.And the largest p(0.97)is obtained in nonploar a-plane Zn0.99Mg0.01O film,resulting from a largest difference in transition energy(30 meV)between E(?)c and E//c caused by a lift of the degeneracy of valence band structures under anisotropic in-plane strains(?yy = 0.4781%,?zz =-0.9251%).(2)Hydrogen plasma treatment has been carried out to improve the optical properties of Zn0.88Mg0.12O,ZnO,and Ga-doped ZnO films.105-fold enhancement of near-band-edge(NBE)emission is obtained in H-plasma treated Zn0.88Mg0.12O film,while 83-fold and 8.6-fold enhancements are obtained in ZnO and Ga-doped ZnO films.By measuring the changes in carrier concentration and the internal quantum efficiency,we attribute the NBE enhancement to the introduction of additional radiative recombination centers and the passivation of nonradiative recombination centers through H-plasma treatment.Besides,the pronounced NBE enhancement differences among Zn0.88Mg0.12O,ZnO,and Ga-doped ZnO films can be illustrated as follows:on one hand,Ga ion with positive trivalence is more repulsive to H ion with positive univalency compared with Zn and Mg ions,resulting in the decrease of the concentration of H in ZnO:Ga film;on the other hand,the passivation of nonradiative recombination centers by H is more prominent in Zn0.88Mg0.12O due to the poorer quality of Zn0.88Mg0.12O.