Bulk ZnO: Current Status, Challenges, and Prospects
VIRGINIA COMMONWEALTH UNIV RICHMOND SCHOOL OF ENGINEERING
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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 capable of producing freestanding ZnO wafers in large-scale for ZnO based device applications, which is the subject matter of this manuscript. Three competing approaches -- hydrothermal 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.