2 results
Effects of Hydrogen Ion Implantation on Structural Properties of Silver Implantation in ZnO Crystals
- Faisal Yaqoob, Mengbing Huang
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1394 / 2012
- Published online by Cambridge University Press:
- 29 February 2012, mrsf11-1394-m12-20
- Print publication:
- 2012
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In this work, we study the effects of implanted hydrogen ions on defect formation and impurity redistribution in ZnO crystals implanted with silver ions. Hydrogen was first implanted at room temperature in ZnO with energy of 30 keV to a dose of 2 × 1016 /cm2. The ZnO samples with and without prior H implantation were implanted with Ag ions at four different energies, 30, 75, 150, and 350 keV, to doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, resulting in a uniform concentration profile of Ag from the surface to depth ~ 150 nm. These samples were annealed at temperatures 850-1050°C for 30 minutes in an oxygen gas flow. The distribution of Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering (RBS) combined with ion channeling. Following Ag ion implantation, the damage level in the ZnO lattice, measured along the <10-11> crystalline direction is higher in the sample without H ion implantation than the sample with H. Lattice damage was found to recover faster in the sample without H implantation than the sample with H, e.g., for Zn signals, the normalized RBS yield χmin for the without H-implanted sample dropped from 27.5% following Ag implantation to 4.3% after annealing at 1050 ˚C, whereas the Zn χmin value for the sample with H implant decreased from 17.6% following Ag implantation to 5.3% after annealing at 1050 ˚C. On the other hand, the χmin values for the Ag dopants before annealing in the H-implanted sample are the same in the sample without H. Post-Ag-implantation annealing resulted in much higher χmin values for Ag in the sample with H implant. For the as-implanted samples, 26.6% of the implanted Ag atoms are on substitutional sites in the sample with H, as compared to 30.3% of the implanted Ag being on the substitutional sites in the sample without H. After annealing at 1050 ˚C, the fraction of substitutional Ag is 73.7% in the H-implanted sample, in contrast to the fraction of 61.6% for substitutional Ag in the sample without H implant. Similar to other oxide crystals, H ion implantation and thermal annealing can result in the formation of nanocavities in the ZnO lattice. We discuss these findings in the context of the effects of nanocavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals.
Diffusion of ion implanted indium and silver in ZnO crystals
- Faisal Yaqoob, Mengbing Huang
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1394 / 2012
- Published online by Cambridge University Press:
- 25 April 2012, mrsf11-1394-m01-10
- Print publication:
- 2012
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We report on diffusion behavior for ion implanted indium and silver atoms in ZnO crystals. Both In and Ag ions were implanted at room temperature at 7-10° relative to c-axis to avoid channeling effects during implantation. In ions were implanted at four different energies (40, 100, 200, and 350 keV, respectively) and doses (4.20×1013, 6.70×1013, 8.10×1013 and 3.10×1014 /cm2, respectively), resulting in a total dose of 5 ×1014 /cm2. For another set of ZnO samples, Ag ions were implanted at energies 30, 75, 150, and 350 keV at doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, to reach a total dose of 5×1014 /cm2. Both In and Ag implants resulted in a uniform concentration profile of the implanted dopants from surface to depth ~ 150 nm. The samples were annealed for 30 minutes at temperatures between 850-1050 °C in an oxygen gas flow. The distributions of In and Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering combined with ion channeling. The diffusivities for nonaligned (interstitial) and aligned (substitutional) dopants atoms were determined to vary with annealing temperature via the Arrhenius relationship. The diffusion activation energies (Ea) along the <10-11> direction for substitutional impurity atoms were lower than those for interstitial dopants atoms e.g., in the case of In, Ea ~ 1.52 eV for <10-11> aligned In atoms and Ea ~ 2.61 eV for interstitial In atoms between <10-11> atomic rows and in the case of Ag, Ea ~ 1.77 eV for the interstitial Ag atoms between the <10-11> atomic rows and 1.11 eV for <10-11> aligned Ag atoms. The diffusion activation energies showed a different trend for the two dopants as measured along the <0001> crystalline direction. For Ag implanted in ZnO, the activation energy of Ea ~ 0.91 eV for the aligned Ag atoms along <0001> direction and Ea ~ 1.55 eV were found for the interstitial Ag atoms, whereas in the case of In along the <0001> direction, the interstitial In was found to migrate with a higher activation energy (Ea ~ 1.78 eV) than the substitutional In (Ea ~1.42 eV). These results will be compared with first-principle calculations for understanding the energetics of defect formation and migration in both n- and p-type doping cases.