Implantation of acceptor ions into ZnO crystals

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SR_2006-019-pdf
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Kennedy, J.V.; Rudolphi, M.; Markwitz, A. 2006 Implantation of acceptor ions into ZnO crystals. Lower Hutt, N.Z.: GNS Science. GNS Science report 2006/19 14 p.

Abstract: Progress in zinc oxide (ZnO) research for optoelectronic applications remains limited due to constraints encountered in producing p-type materials in either thin films or bulk crystals. Production of p-type ZnO material would create a major advance towards producing materials with superior electronic and optical properties given that as grown ZnO typically has n-type conductivity. The aim of the present study is to establish an implantation protocol for nitrogen as an acceptor ion, into n-type ZnO crystals to produce p-type ZnO for various optoelectronic applications. DYNAMIC-TRIM calculations have been performed to obtain N profiles for the various doses used between 1x1014 ions cm-2 and 1x1017 ions cm-2. The calculations revealed a mean projected range of 45 nm coupled with a maximum implantation depth of ~ 80 nm. For these fluences, the N peak concentration varies between 0.05 and 17 at.%. At fluences larger than 1 x 1016 N cm-2, the N profile intersects with the surface. We have successfully implanted 23 keV N with various fluences ranging from 1x1014 ions cm-2 to 1x1017 ions cm-2 using the newly established ion implantation facility at GNS. The implanted N concentration has been measured by ion beam analysis technique of nuclear reaction analysis (NRA). It was found that the measured concentrations are very close to the calculated values. NRA results have also shown that we can detect N as low as 8x1014 ions cm-2 in the ZnO materials. Raman spectroscopy has been used to study the structural properties of N implanted ZnO. Raman measurements on the N implanted samples have suggested three additional modes at 275, 504, and 644 cm-1, in comparison with un-implanted ZnO crystals. As per literature, the mode at 275 cm-1 originates from vibration of Zn atoms, where some of its first nearest neighbour O atoms are replaced by N atoms in the crystal lattice. The other two modes probably arise from the optical phonon branch at the zone boundary induced by damage of the crystal lattice. It was found that the intensity of the mode at 275 cm-1 increase as the implantation fluences increases. The NRA and Raman results have provided information about the implanted N concentration, depth and its structural changes with respect to various nitrogen ion fluences, in order to establish the protocol to produce p-type ZnO using the GNS low energy ion implantation facility. (auth)