A View of the Past, and a Look into the Future by a Pioneer By Jacques I. Pankove This forword will be a brief review of important developments in the early and recent history of gallium nitride, and also a perspective on the current and future evolution of this exciting field. Gallium nitride (Ga N) was syn- thesized more than 50 years ago by Johnson et al. [1] in 1932, and also by Juza and Hahn [2] in 1938, who passed ammonia over hot gallium. This method produced small needles and platelets. The purpose of Juza and Hahn was to investiagte the crystal structure and lattice constant of Ga N as part of a systematic study of many compounds. Two decades later, Grim- al. [3] in 1959 employed the same technique to produce small cry- meiss et stals of Ga N for the purpose of measuring their photoluminescence spectra. Another decade later Maruska and Tietjen [4] in 1969 used a chloride trans- port vapor technique to make a large-area layer of Ga N on sapphire. All of the Ga N made at that time was very conducting n-type even when not deli- berately doped. The donors were believed to be nitrogen vacancies. Later this model was questioned by Seifert et al. [5] in 1983, and oxygen was pro- as the donor. Oxygen with its 6 valence electrons on a N site (N has 5 posed valence electrons) would be a single donor.
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