Materials Processing for ZnO

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This project focuses on two research areas related to utilization of ZnO as a technological mate-rial-ohmic contact formation, and the exploration and potential exploitation of ferromagnetism in doped ZnO. Greater understanding of fundamental materials science associated with stable, low resistance ohmic contacts to ZnO; plasma chemistries for dry etching of ZnO; implanta-tion/isolation needed in selective area doping for contact formation and for intra-device electrical and optical isolation; and the role of hydrogen on electrical and magnetic properties of ZnO is sought. Rationale for the project includes potential ZnO application to UV light emitters, varistors, transparent high power electronics, surface acoustic wave devices, piezoelectric transducers, gas-sensing and as a window material for display and solar cells. It has advantages relative to GaN because of its availability in bulk, single crystal form and its larger exciton binding energy (~60meV, cf. ~25meV for GaN). In addition, ZnO is lattice-matched to InGaN at an In composition of ~22%, raising the possibility of integration of the two materials to provide enhanced functionality. This may have applications in high-density data storage systems, solid-state lighting (where white light is obtained from phosphors excited by blue or UV light-emitting diodes), se-cure communications and biodetection. The properties of ZnO compare well with those of GaN. ZnO is a direct bandgap semiconductor with Eg = 3.2 eV. The bandgap can be tuned via divalent substitution on the cation site. Cd substitution leads to a reduction in the bandgap to ~ 3.0 eV. Substituting Mg on the Zn site can increase the bandgap to approximately 4.0 eV while still maintaining the wurtzite structure. The electron Hall mobility in ZnO single crystals is on the order of 200 cm2/V-sec at room temperature. The electron mobility is slightly lower than for GaN, but ZnO has a higher saturation velocity. %%% This project addresses basic research issues in a topical area of materials science with significant technological relevance, and places emphasis on the integration of research and education. At least two undergraduates will be included in this project. Persons from under-represented groups (women, minorities) will be particularly encouraged to participate. Additionally, as part of this grant activity, the PI will host 2 students attending the U. FL Student Science Training Program, which is run during the summer by the U. FL Center for Precollegiate Education and Training. This program, now in its 41st year, brings in 10th and llth grade students to actively participate in science and engineering research. The Center for Precollegiate Education and Training at the University of Florida also runs an NSF Teacher Research Update Experience (TRUE) program during the summer. The PI will present a lecture on ZnO at the program and will collaborate with interested teachers to translate the research experience here into modules, which can be taken back to the middle and high schools. ***