Zinc oxide: a material for efficient light emission
EMSL Project ID
22290
Abstract
Zinc oxide (ZnO) is a semiconductor that has attracted resurgent interest as an electronic material for a range of applications. A wide-bandgap semiconductor, ZnO emits light in the blue-to-UV region of the spectrum. The efficiency of the emission is higher than more conventional materials such as GaN, making ZnO a strong candidate for energy-efficient white lighting. Despite its numerous advantages and potential applications, ZnO suffers from a major drawback: as grown, it contains a relatively high level of donors. These defects and impurities compensate acceptors or donate free electrons to the conduction band, thereby preventing p-type conductivity. We propose a coordinated program of growth and characterization of ZnO thin films doped with N acceptors. Our approach to produce p-type material involves the incorporation of neutral N-H complexes. The formation of such complexes, on first glance, would seem to be detrimental, since the passivation of acceptors prevents p-type doping. However, the formation of N-H complexes should suppress the formation of compensating donor defects. The hydrogen will then be driven off by post-growth annealing, as is commonly done with GaN:Mg.
Thin ZnO films will be grown using the metalorganic chemical vapor deposition (MOCVD) system at EMSL. Zn(TMHD)2 will be used as the precursors for ZnO, and N2 plasma will be used as the precursor for nitrogen doping. The growth temperature and gas flow rates will be varied systematically to optimize the crystal quality and maximize the concentration of N-H complexes.
IR spectroscopy will be performed on ZnO thin films, in order to determine the concentration and structure of N-H complexes. The high sensitivities of the Fourier transform infrared (FTIR) system will enable precise characterization of hydrogen in ZnO. Low-temperature spectroscopy, utilizing low-noise germanium detectors that operate at liquid-helium temperatures, will be used to provide the highest level of signal to noise. The concentration, mobility, and type (electron or hole) of charge carriers in ZnO will be measured with our variable-temperature Hall-effect apparatus. By varying the temperature over a wide range (80 to 700 K), it will be possible to determine the existence and activation energy of acceptors in ZnO.
A physics Ph.D. student will perform MOCVD growth at PNNL, under the supervision of Dr. Laxmikant Saraf. The student will perform sample characterization at WSU, under the supervision of Dr. Matthew McCluskey. During the first growth runs, we will grow thin films on silicon substrates. After reasonable growth parameters have been established, homoepitaxial growth will be performed on ZnO substrates obtained from Cermet, Inc.
IR spectroscopy will be used to determine the concentration of N-H complexes incorporated in the ZnO film. A series of isochronal anneals will be performed. As the N-H complexes dissociate, we should observe a decrease in the N-H IR signature and a corresponding increase in the free hole concentration.
Project Details
Project type
Exploratory Research
Start Date
2006-10-21
End Date
2007-08-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Hlaing Oo WM, LV Saraf, MH Engelhard, V Shutthanandan, and MD Mccluskey. 2009. "Suppression of conductivity in Mn-Doped ZnO Thin Films." Journal of Applied Physics 105(1):013715. doi:10.1063/1.3063730
Johnson GE, CM Wang, TA Priest, and J Laskin. 2011. "Monodisperse Au11 Clusters Prepared by Soft Landing of Mass Selected Ions." Analytical Chemistry 83(21):8069-8072. doi:10.1021/ac202520p
L.V. Saraf, W.M.H. Oo, Z.H. Zhu, C.M. Wang, M.H. Engelhard, D.R. Baer and M.D. McCluskey, "Solubility and Secondary Phase Segregation Relationship for Favorable Vs Unfavorable Dopants in Oriented/Epitaxial ZnO Films Grown by MOCVD," Spring 2008 MRS abstract.