ZnCdO/ZnMgO and ZnO/AlGaN Heterostructures for UV and Visible Light Emitters
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0892-FF18-01-EE09-01.1
ZnCdO/ZnMgO and ZnO/AlGaN Heterostructures for UV and Visible Light Emitters A. V. Osinsky1, J. W. Dong1, J. Q. Xie1, B. Hertog1, A. M. Dabiran1, P. P.Chow1, S. J. Pearton2, D. P. Norton2, D. C. Look3, W. Schoenfeld4, O. Lopatiuk4, L. Chernyak4, M. Cheung5 A.N. Cartwright5 and M. Gerhold6 1
SVT Associates, 7620 Executive Drive, Eden Prairie, MN 55344 University of Florida, Gainesville, FL 32611 3 Wright State University, Dayton, OH 4 University of Central Florida, Orlando, FL 32819 5 University at Buffalo, Buffalo, NY 14260 6 U.S. Army Research Office, Durham, NC 2
ABSTRACT This paper reviews of some of the progress made in the development of ZnO-based light emitting diodes (LEDs). n-ZnO/p-AlGaN-based heterostructures have been successfully for the fabrication of UV emitting LEDs that have operated at temperatures up to 650K, suggesting an excitonic origin for the optical transitions. RF-plasma-assisted molecular beam epitaxy has been used to grow epitaxial CdxZn1-xO films on GaN/sapphire structure. These films have a singlecrystal wurtzite structure as demonstrated by structural and compositional analysis. High quality CdxZn1-xO films were grown with up to x=0.78 mole fraction as determined by RBS and SIMS techniques. Optical emission ranging from purple (Cd0.05Zn0.95O) to yellow (Cd0.29Zn0.71O) was observed. Compositional fluctuations in a Cd0.16Zn0.84O films were not detected by spatially resolved CL measurements, although intensity fluctuation with features of ~0.5 µm diameter were seen on the intensity maps. Time resolved photoluminescence shows multi-exponential decay with 21 psec. and 49±3 psec. lifetimes, suggesting that composition micro-fluctuations may be present in Cd0.16Zn0.84O film. INTRODUCTION The ZnO based material system has attracted considerable attention recently as a possible candidate for ultraviolet to visible emitters. ZnO has a much higher free-exciton binding energy of 60 meV [1, 2] than other wide band gap materials like GaN and SiC, leading to efficient excitonic optical transitions at elevated temperatures. It is also possible to tune the band gap of ZnO (~3.37 eV) by alloying to produce compounds with band gaps wider or narrower than that of ZnO alone. In particular, MgxZn1-xO compounds with band gaps of over 6 eV have already been successfully formed by alloying with the dielectric MgO which has a RT band gap of 7.9eV. Moreover, as suggested by results presented in this paper and elsewhere, ZnCdO is a promising candidate to cover the narrow band gap spectrum. This is not unexpected since CdO has a RT band gap of 2.3 eV and Zn and Cd atoms have similar ionic radii. The tunability of the ZnO band gap enables light emission over a broad spectrum, i.e., from the deep UV to the visible regime, and can also allow the formation of both energy barriers and quantum wells that can provide more effective quantum confinement and increased internal quantum efficiency. The tunability greatly increases the perspective applications for this material system.
0892-FF18-01-EE
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