An examination of the surface decomposition chemistry of lithium niobate precursors under high vacuum conditions

We employ a combination of high vacuum (chemical beam) epitaxy and in situ mass spectrometry to examine precursor surface decomposition chemistry duri ng film growth of LiNbO3 and its constituent metal oxides on sapphire and S i (001). The four most common CVD precursors for LiNbO3 - [Li(OBut)](6), Li (tmhd), [Nb(OEt)(5)](2), and Nb(tmhd)(4) - are examined (OBut = tertiary bu toxide, OEt = ethoxide, tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate). The metal diketonates are unstable at low pressures and temperatures, adversel y impacting both storage and use. The metal alkoxides, while of greater the rmodynamic stability, are subject to autocatalytic processes that can inhib it the film growth: these processes generate volatile metal-containing moie ties that subsequently desorb from the surface. The degree of crystallinity of niobium oxide films grown from [Nb(OEt)(5)](2) depends on the presence of one of the autocatalytic elements, water. The growth rate of lithium nio bate films depends strongly on the Li/Nb precursor ratio, suggesting a chem ical interaction between the two precursors. (C) 2000 Published by Elsevier Science B.V. All rights reserved.