Pt/Au and W/Pt/Au Schottky Contacts to Bulk n-ZnO.
- PDF / 102,374 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 88 Downloads / 196 Views
B10.1.1
Pt/Au and W/Pt/Au Schottky Contacts to Bulk n-ZnO. Kelly Ip1, Brent Gila1, Andrea Onstine1, Eric Lambers1, Young-Woo Heo1, David Norton1, Stephen Pearton1, Jeffrey LaRoche2 and Fan Ren2; 1 Materials Science and Engineering, University of Florida, Gainesville, Florida 2 Chemical Engineering, University of Florida, Gainesville, Florida. ABSTRACT UV-ozone cleaning prior to metal deposition of either e-beam Pt contacts or sputtered W contacts on n-type single-crystal ZnO is found to significantly improve their rectifying characteristics. Pt contacts deposited directly on the as-received ZnO surface are Ohmic but show rectifying behavior with ozone cleaning. The Schottky barrier height of these Pt contacts was 0.70 eV, with ideality factor of 1.5 and a saturation current density of 6.2 × 10-6 A⋅cm-2. In contrast, the as-deposited W contacts are Ohmic, independent of the use of ozone cleaning. Post-deposition annealing at 700 °C produces rectifying behavior with Schottky barrier heights of 0.45 eV for control samples and 0.49 eV for those cleaned with ozone exposure. The improvement in rectifying properties of both the Pt contacts is related to removal of surface carbon contamination from the ZnO. INTRODUCTION ZnO is currently under development for use in UV light emitters, spin functional devices, gas sensors, transparent electronics and surface acoustic wave devices(1-14). It has a direct bandgap energy of 3.3 eV and large exciton binding energy of 60 meV, which makes it well-suited to developing high brightness UV light sources and transparent electronics. To realize UV light emitters/detectors or field effect transistors ,it is necessary to develop reliable ,reproducible doping methods and Ohmic and rectifying contacts to this material in order to exploit these device opportunities. Previous reports have shown Au, Ag and Pd form rectifying contacts on n-type ZnO with Schottky barrier heights in the range of 0.6-0.8 eV (12-32) .However, the trend in barrier heights did not correlate with the metal work functions, suggesting that either intrinsic surface states or residual surface contamination is playing a role in determining the electrical properties of the contacts. In addition, the thermal stability of Au was extremely poor, with degradation occurring even at 60 °C (23-27). Various surface cleaning procedures prior to depositing contacts on ZnO have been reported, such as etching in concentrated phosphoric or nitric acid or organic solvent rinsing (23-25). However, in most cases the reported ideality factors are high, indicating the presence of transport mechanisms such as tunneling, the impact of interface states or the influence of deep recombination centers. In this letter we demonstrate the UV ozone cleaning of the n-type ZnO surface prior to deposition of either e-beam Pt or sputtered W contacts produces significant improvements in the rectifying properties of these contacts and that W contacts are stable up, to ~700°C. The samples were the (0001) undoped grade I quality bulk ZnO crystals from Cermet.
Data Loading...
