Autostoichiometric vapor deposition: Part II. Experiment
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An autostoichiometric vapor deposition method is implemented to achieve deposition of stoichiometric LiTaO3 using LiTa(OBut")6 precursor. Precisely stoichiometric LiTaO3 can be grown by this method. A simple low pressure reactor is used to facilitate the autostoichiometric vapor deposition through hydrolysis polycondensation of double alkoxides in the vapor phase. Typical deposition and annealing conditions are described. X-ray diffraction, SEM, and compositional analyses are performed on the films grown on fused silica, Pt, (100) sapphire, and LiNbO3(001). Rocking curve measurements indicated excellent epitaxial growth of LiTaO3 on (100) sapphire. Compositional analysis by measurement of lattice parameters confirmed that the present method can produce high quality stoichiometric LiTaO3. The nonstoichiometry factor for LiTa(OBut")6 is negligible. Mass spectrometric study of the precursor compound LiTa(OBut")6 suggests that the volatile species is Li2Ta2(OBut")12.
I. INTRODUCTION 1
In a previous paper it was suggested that an inherently stoichiometric method can be implemented for the vapor deposition of certain multicomponent oxides. One possible route is by using volatile double alkoxide precursors and the hydrolysis-polycondensation of precursors in a low pressure reactor. Precisely stoichiometric ferroelectrics such as LiNbO 3 , KNbO 3 , and LiTaO3 can be deposited according to the following reactions: ABn(OR)2m
+ 2fcH2O vaP°r-Phase, ABn(OH)2k(OR)2im-k)
+ ikHOR,
ABn(OH)2k(OR)2im-k)on-subslrile' ABnOk(OR)2(n- (n k) ABnOk(OR)2(m-k
(m - k)H2O
ABnOm
(1)
, (2)
°"- s " bstrate ,
+ 2(m - k)HOR.
(3)
In this paper, we shall demonstrate experimentally the feasibility of autostoichiometric vapor deposition of LiTaO3 from a LiTa(OBut")6 precursor. The choice of the oxide system and precursor compound is limited by the thermal stability of the precursor compound. Alkoxide chemistry2 suggests that, in general, the vapor pressure and stability of a double alkoxide increase with increasing alkoxy group length. In terms of the elements, stability decreases in the order of Li>Na>/f, and Ta>Nb. Therefore, it is natural to test the system LiTaO3 with a double alkoxide LiTa(OR)6 having a long chain alkoxy group. 2542
J. Mater. Res., Vol. 10, No. 10, Oct 1995
http://journals.cambridge.org
Downloaded: 17 Mar 2015
From the materials point of view, ferroelectric LiTaO3 is an excellent candidate for integrated optic applications due to its high electro-optic and piezoelectric coefficients. It is also an attractive candidate for IR detectors due to its relatively high pyroelectric coefficient, high Curie temperature, and fast response. Presently, there is considerable interest in LiTaO3 for second harmonic generations.3-4 For applications where relatively high power lasers are used, optical damage to the electro-optic waveguide caused by defects associated with off-stoichiometry in LiTaO35'6 becomes a critical issue. It is well known that LiTaOa has an offstoichiometric congruent melting point at 48.75 mol % of Li 2 O, 7
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