Soluble semiconductors AAsSe{sub 2} (A = Li, Na) with a direct-band-gap and strong second harmonic generation : a combined experimental and theoretical study.
- Materials Science Division
AAsSe{sub 2} (A = Li, Na) have been identified as a new class of polar direct-band gap semiconductors. These I-V-VI{sub 2} ternary alkali-metal chalcoarsenates have infinite single chains of (1/{infinity})[AsQ{sub 2}{sup -}] derived from corner-sharing pyramidal AsQ{sup 3} 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 Li1-xNaxAsSe{sub 2} stoichoimetry ({alpha}-LiAsSe{sub 2}, {beta}-LiAsSe{sub 2}, {gamma}-NaAsSe{sub 2}, and {delta}-NaAsSe{sub 2}). Single-crystal X-ray diffraction studies showed an average cubic NaCl-type structure for {alpha}-LiAsSe{sub 2}, which was further demonstrated to be locally distorted by pair distribution function (PDF) analysis. The {beta} and {gamma} forms have polar structures built of different (1/{infinity})[AsSe{sub 2}{sup -}] chain conformations, whereas the {delta} form has nonpolar packing. A wide range of direct band gaps are observed, depending on composition: namely, 1.11 eV for {alpha}-LiAsSe{sub 2}, 1.60 eV for LiAsS{sub 2}, 1.75 eV for {gamma}-NaAsSe{sub 2}, 2.23 eV for NaAsS{sub 2}. The AAsQ{sub 2} 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 {gamma}-NaAsSe{sub 2} 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 {gamma}-NaAsSe{sub 2} has the highest static SHG coefficient known to date, 337.9 pm/V, among materials with band gaps larger than 1.0 eV.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 1008298
- Report Number(s):
- ANL/MSD/JA-69074; TRN: US201106%%386
- Journal Information:
- J. Am. Chem. Soc., Vol. 132, Issue Feb. 19, 2010
- Country of Publication:
- United States
- Language:
- ENGLISH
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