Emergence of Chalcopyrites as Nonlinear Optical Materials

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Abstract
Chalcopyrite nonlinear optical (NLO) semiconductors are presently enjoying a major renaissance. This rebirth of interest is due primarily to the success of recent materials research-and-development (R&D) programs that have dramatically improved the availability of large crackfree high-quality crystals. This overview provides a general review of chalcopyrites, of their application in laser systems that exploit second-harmonic generation (SHG) or optical parametric oscillation (OPO), and of the materials-selection criteria for laser crystals to assist in focusing R&D efforts. It also suggests broader application areas. The overview concludes with a number of specific recommendations for further R&D efforts to advance this materials technology.The archetype infrared NLO chalcopyrites are AgGaSe2 (a I-III-VI2 semiconductor) and ZnGeP2 (a II-IV-V2 semiconductor). Using samples of naturally occurring pyrites, Pauling correctly established the chalcopyrite's crystal structure (diamondlike where Zn and Ge cations are ordered) in 1932 after two previous false starts by others. Levine, who has extensively studied the nonlinear susceptibilities of a number of bond types, stated in 1973 that the chalcopyrite structure is so favorable for NLO properties that it will be difficult to ever find materials with larger nonlinearities in the infrared spectral region. That statement has proved to be prophetic.Goodman of Great Britain first reported that chalcopyrites were semiconductors. However the first observation that these materials were semiconductors is generally attributed to A.F. Ioffe and N. A. Goryunova of the A.F. Ioffe Physico-Technical Institute (IPT) in St Petersburg, Russia.