Microwave Growth of ZnO Bulk Crystals
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1035-L04-04
Microwave Growth of ZnO Bulk Crystals Jiping Cheng1, Yunjin Zhang1, and Ruyan Guo2 1 Materials Research Institute, The Pennsylvania State University, University Park, PA, 16802 2 Department of Electrical and Computer Engineering, The University of Texas at San Antonio, San Antonio, TX, 78249 ABSTRACT A novel approach for fabricating ZnO crystals using self-encapsulated microwave melt growth technique is developed, which permits idealized temperature profile for the nucleation of the ZnO crystals and their growth in a contamination-free environment. This paper reports that both un-doped ZnO and p-type doped ZnO (by P or Li:N doping) single crystals were successfully fabricated by this technique. The as-grown ZnO crystals were of light brown to clear in color depending on processing conditions. Their transparency and colorless form were restored after post-growth annealing in oxygen. INTRODUCTION Zinc oxide (ZnO) is a II-VI semiconductor with direct bandgap around 3.4 eV that has been studied and used for a long time due to its excellent piezoelectric, optical and semiconductor properties for a wide range of applications, such as piezoelectric transducers, varistors, optical waveguides, conductive gas sensors, acousto-optic media, and transparent electrodes. Starting in the middle of 1990’s, ZnO attracted a wide interest again due in a large part to the successes in producing large size single crystals, high quality epitaxial layers, nanorods, nanowires, nano/micro tubes, and quantum wells/dots, that have opened up the possibility of producing blue and UV optoelectronics, including light emitters, laser diodes, and high-temperature, high-power electronic devices [1-4]. ZnO has wurtzite structure analogous to GaN. The lattice constant mismatch between ZnO and GaN is
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