Chalcoarsenate semiconductors as emerging mid-IR second harmonic generation materials: A combined experimental and theoretical study.

摘要

Non-centrosymmetric (NCS) semiconductors exhibit second harmonic generation (SHG) and other nonlinear optical (NLO) responses. Of much current interest is the mid-IR (2--20 mum) region, a spectral range of importance for molecular spectroscopy, atmospheric sensing, and various optoelectronic devices. The synthetic investigation in the arsenic chalcogenide based material area is motivated by the fact that the non-centrosymmetric material with asymmetric pyramidal AsQ3 (Q = S, Se) units and a stereochemically active lone-pair of electrons on the arsenic atoms could act as an enhancing factor for the SHG response. Novel semiconductors AAsQ2 (A = Li, Na; Q = S, Se) with pyramidal unit AsQ3 were synthesized and characterized by single-crystal X-ray diffraction analysis. They show remarkably high SHG response, which can reach up to ∼75 times relative to the commercial bench-mark SHG material AgGaSe2. The first principles SHG susceptibility calculation showed a static SHG coefficient [chi(2)] of 324.6 pm/V (for gamma-NaAsSe 2), which is the highest SHG coefficient reported to date. The search for better SHG materials was extended into the quaternary system A3Ta 2AsS11 (A = K, Rb, and Cs) in an attempt to introduce two different asymmetric building units in one structure. Overall the thesis is about three different approaches used to design new materials with improved SHG response (Chapter 3, 4, and 5). The use of arsenic-rich polychalcogenide flux to stabilize the As3+ species instead of As5+ species is presented in Chapter 6, 7, and 8.