Soluble Semiconductors AAsSe2 (A = Li, Na) with a Direct-Band-Gap and Strong Second Harmonic Generation: A Combined Experimental and Theoretical Study

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• 作者：Tarun K. Bera ; Joon I. Jang ; Jung-Hwan Song ; Christos D. Malliakas ; Arthur J. Freeman ; John B. Ketterson ; Mercouri G. Kanatzidis
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：March 17, 2010
• 年：2010
• 卷：132
• 期：10
• 页码：3484-3495
• 全文大小：524K
• 年卷期：v.132,no.10(March 17, 2010)
• ISSN：1520-5126

文摘

AAsSeb>2b> (A = Li, Na) have been identified as a new class of polar direct-band gap semiconductors. These I−V−VIb>2b> ternary alkali-metal chalcoarsenates have infinite single chains of (1/∞)[AsQb>2b>⁻] derived from corner-sharing pyramidal AsQb>3b> units with stereochemically active lone pairs of electrons on arsenic. The conformations and packing of the chains depend on the structure-directing alkali metals. This results in at least four different structural types for the Lib>1−xb>Nab>xb>AsSeb>2b> stoichoimetry (α-LiAsSeb>2b>, β-LiAsSeb>2b>, γ-NaAsSeb>2b>, and δ-NaAsSeb>2b>). Single-crystal X-ray diffraction studies showed an average cubic NaCl-type structure for α-LiAsSeb>2b>, which was further demonstrated to be locally distorted by pair distribution function (PDF) analysis. The β and γ forms have polar structures built of different (1/∞)[AsSeb>2b>⁻] chain conformations, whereas the δ form has nonpolar packing. A wide range of direct band gaps are observed, depending on composition: namely, 1.11 eV for α-LiAsSeb>2b>, 1.60 eV for LiAsSb>2b>, 1.75 eV for γ-NaAsSeb>2b>, 2.23 eV for NaAsSb>2b>. The AAsQb>2b> materials are soluble in common solvents such as methanol, which makes them promising candidates for solution processing. Band structure calculations performed with the highly precise screened-exchange sX-LDA FLAPW method confirm the direct-gap nature and agree well with experiment. The polar γ-NaAsSeb>2b> shows very large nonlinear optical (NLO) second harmonic generation (SHG) response in the wavelength range of 600−950 nm. The theoretical studies confirm the experimental results and show that γ-NaAsSeb>2b> has the highest static SHG coefficient known to date, 337.9 pm/V, among materials with band gaps larger than 1.0 eV.