Optical and structural properties of doped ZnO nanocrystals
EMSL Project ID
42310
Abstract
Zinc oxide (ZnO) is a semiconductor that has attracted resurgent interest as an electronic material for energy applications. With a direct gap of 3.4 eV at room temperature, ZnO is a wide band gap semiconductor that emits light in the near-UV region of the spectrum. The high efficiency of the emission makes ZnO a strong candidate for solid-state white lighting. The use of nanoscale semiconductors provides several advantages over bulk materials, including band-gap tunability and applications such as dye-sensitized solar cells. While semiconductor nanocrystals have received a huge amount of attention, comparatively little is known about the fundamental properties of dopants in these materials. Dopants and defects in ZnO nanocrystals are only beginning to be understood. In the proposed work, we aim to: >Determine the microscopic structure of H complexes in ZnO nanocrystals >Investigate the effect of particle size on dopant concentration and charge state >Probe H and Cu energy levels as a function of quantum confinement, alloying, and pressure. >Investigate the effect of Cu doping on the optical properties of ZnO nanocrystals and ceramics >Achieve p-type doping of ZnO nanocrystals. To achieve these goals, we will pursue a coordinated program of synthesis and optical characterization at WSU and UI. Structural, compositional, and defect characterization will be performed at EMSL user facilities. The proposed work builds on a long-term collaboration between the three groups. At EMSL, x-ray diffraction (XRD) will be used to characterize the crystal structure and average diameter of ZnO nanocrystals. Transmission electron microscopy (TEM) will be used to obtain accurate data about particle size and dispersion, as well as surface layers such as Zn(OH)2. EMSL is currently in the process of procuring a new generation TEM/STEM system that will provide point-to-point resolution of better than 1 angstrom, enabling us to achieve a new level of detail. X-ray photoelectron spectroscopy (XPS) will be performed to characterize the concentration and charge state of Cu, Mg, and other elements. Secondary ion mass spectrometry (SIMS) will be utilized to quantify the concentration of impurities. Electron paramagnetic resonance (EPR) will be performed to probe electron and hole spins at temperatures from 5-300 K, providing quantitative information about donor and acceptor dopants. One graduate student (Samuel Teklemichael) has been trained on the TEM at EMSL, under the supervision of Dr. Chongmin Wang, and is working with the group of David Hoyt on EPR experiments. Additional graduate students will be trained and make regular trips to EMSL.
Project Details
Project type
Exploratory Research
Start Date
2010-12-27
End Date
2012-01-01
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Teklemichael ST, WMH Oo, MC Matthew, ED Walter, and DW Hoyt. 2011. "Acceptors in ZnO nanocrystals." Applied Physics Letters 98(23):Article No. 232112. doi:10.1063/1.3598411