Zinc oxide nanocluster formation by low energy ion implantation
- PDF / 152,788 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 43 Downloads / 230 Views
B2.21.1
Zinc oxide nanocluster formation by low energy ion implantation I. Muntele*, P. Thevenard*,**, C. Muntele*, B. Chhay*, D. Ila* *
Center for Irradiation of Materials, Alabama A&M University, NORMAL AL-35762, USA ** LPMCN, UMR CNRS 5586, Universite Claude Bernard LYON, 699622 VILLEURBANNE Cedex FRANCE
Abstract Variable size nanocluster embedded in silicon substrate were obtained by low energy implantation methods. We used optical spectroscopy to measure the optical properties of the implanted samples. The implantation parameters like the ions energy, dose and sputtering rate were calculated with SRIM [13]. Most of the implanted Zn ions (83%) clustered and oxidized during the implantation process, with the remaining 17% being oxidized during annealing in air.
Introduction Zinc oxide is one of the most interesting wide band-gap semiconductor, due to its 3.37 eV direct band-gap and the large exciton energy of 60 meV1-2 at 300K. It is easily n-type doped1-2 while p-type doping3-5 is much more difficult, as in equivalent large band-gap semiconductors like GaN. This is due to the low dielectric constant and then impurity orbitals are very contracted4. Because of its optical, electrical and piezoelectric properties, ZnO is involved in many applications6-8 such as: UV light emitters, UV lasers, non linear optics, transparent electronics, solar cells, MEMS devices, gas sensors, field emission, spintronics. Due to quantum confinement effects, the ability to fabricate ZnO at controlled nanocluster sizes enhanced the potential for new applications9-11. Quantum confinement effects in ZnO quantum dots (QDs) of few nanometers, can lead to new applications in ultraviolet luminescent devices particularly when QDs are localized in very high electric field. The confinement of exciton wave functions increases the energy of the band gap compared with that in the bulk and divides it into a set of discrete levels. Quantum confinement has to be observed when the size of the nanoclusters approaches the Bohr radius of the exciton. The energy of the lowest excited state (comparable to the energy gap of the nanocluster) for a spherical particle of radius R is estimated by the following formula12:
E = Eg +
⎡ 1 h2 1 ⎤ 1.8e 2 ε − + ∞⎢ ⎥ 8mo R 2 ⎣ me* mh* ⎦ 4πε oε ∞ R
where E g is the band gap of the bulk material. The second term is a confinement term and varies as 1/R2 and the third term is the Coulomb attraction term varying as 1/R.
B2.21.2
The band gap optical absorption and the associated emission band are then strongly dependent on cluster sizes.
Experiment and Discussion Intrinsic silicon wafers were implanted at room temperature with 6x1015 20 keV Zn ions/cm2. The resulting samples were annealed for 30 minutes in air at 1000oC. Separately, silicon cuts from the same wafer were annealed in the same conditions for comparison purposes. The implantation was done 7 degrees of the (100) axis in order to avoid channeling effects. The total surface sputtering as calculated from SRIM was approximately 3 nm. Figure 1 shows the range
Data Loading...
