George, Kathryn, de Groot, Cornelis H., Gurnani, Chitra, Hector, Andrew L., Huang, Ruomeng, Jura, Marek, Levason, William, Reid, Gillian and Huang, R. (2013) Telluroether and Selenoether complexes as single source reagents for low pressure chemical vapor deposition of crystalline Ga2Te3 and Ga2Se3 thin films. Chemistry of Materials, 25 (9), 1829-1836. (doi:10.1021/cm400382j).
Abstract
The neutral complexes [GaCl3(EnBu2)] (E = Se or Te), [(GaCl3)2{nBuE(CH2)nEnBu}] (E = Se, n = 2; E = Te, n = 3), and [(GaCl3)2{tBuTe(CH2)3TetBu}] are conveniently prepared by reaction of GaCl3 with the neutral EnBu2 in a 1:1 ratio or with nBuE(CH2)nEnBu or tBuTe(CH2)3TetBu in a 2:1 ratio and characterized by IR/Raman and multinuclear (1H, 71Ga, 77Se{1H}, and 125Te{1H}) NMR spectroscopy, respectively, all of which indicate distorted tetrahedral coordination at Ga. The tribromide analog, [GaBr3(SenBu2)], was prepared and characterized similarly. A crystal structure determination on [(GaCl3)2{tBuTe(CH2)3TetBu}] confirms this geometry with each pyramidal GaCl3 fragment coordinated to one Te donor atom of the bridging ditelluroether, Ga–Te = 2.6356(13) and 2.6378(14) Å. The nBu-substituted ligand complexes serve as convenient and very useful single source precursors for low pressure chemical vapor deposition (LPCVD) of single phase gallium telluride and gallium selenide, Ga2E3, films onto SiO2 and TiN substrates. The composition and morphology were confirmed by SEM, EDX, and Raman spectroscopy, while XRD shows the films are crystalline, consistent with cubic Ga2Te3 (F‾43m) and monoclinic Ga2Se3 (Cc), respectively. Hall measurements on films grown on SiO2 show the Ga2Te3 is a p-type semiconductor with a resistivity of 195 ± 10 Ω cm and a carrier density of 5 × 1015 cm–3, indicative of a close to stoichiometric compound. The Ga2Se3 is also p-type with a resistivity of (9 ± 1) × 103 Ω cm, a carrier density of 2 × 1013 cm–3, and a mobility of 20–80 cm2/V·s. Competitive deposition of Ga2Te3 onto a photolithographically patterned SiO2/TiN substrate indicates that film growth onto the conducting and more hydrophobic TiN is preferred.
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