Rediscovered in the last decade, zinc oxide (ZnO) has attracted much attention as a promising material for many optoelectronics and to some extent microelectronics applications. However, a clear majority of effort expended in this fast developing field has been limited to heteroepitaxial structures grown on foreign substrates with lattice-parameter and thermal-expansion mismatch with ZnO which is detrimental. Recognizing the importance, the effort has shifted to include developing technologies

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... apable of producing freestanding ZnO wafers in large-scale for ZnO based device applications, which is the subject matter of this manuscript. Three competing approacheshydrothermal method, melt growth (modifications of the well known Bridgman technique), and seeded vapor transport growth (or sublimation) -have now reached the level which can be construed as commercialization. In this article, we discuss the progress, outstanding problems, and prospects of these growth methods employed for commercial manufacturing of ZnO wafers. Index Terms-Zinc oxide, single crystals, hydrothermal method, Bridgman method, vapor transport solvent, which forms metastable products with the ZnO solute (nutrient). The KOH/LiOH mineralizer is used to enhance the solubility of the nutrient. Although somewhat slow, the hydrothermal method driven by a small amount of supersaturation of the solution is viewed as a scalable process for production of large quantities of large area ZnO. However, the hydrothermally grown ZnO contains relatively large amount of K and, especially, Li incorporated from the mineralizer, which have detrimental effects on the epitaxial films grown on hydrothermal-ZnO wafers due to outdiffusion. Below we discuss basic characteristics, current status, commercial potential, and challenges facing the three aforementioned growth methods in some detail. A. Melt growth Melt crystal growth involves the controlled deposition of atoms onto a single-crystal seed from molten raw materials by making use of the liquid-to-solid phase transition caused by the temperature gradient. The Czochralski and Bridgman methods are the most common melt-growth techniques used for production of bulk single-crystal ingots. The Bridgman Bulk ZnO: Current Status, Challenges, and Prospects A brief overview of the recent achievements in mass production of ZnO single crystals Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. Same as Report (SAR) 18. NUMBER OF PAGES 11 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 Vitaliy Avrutin received M.S. degree in Electrical Engineering with Honors from