From Molecular Gallium and Indium Siloxide Precursors to Amorphous Semiconducting Transparent Oxide Layers for Applications in Thin-Film Field-Effect Transistors

The syntheses, structural characterization, and thermal degradation of a series of the new indium and gallium siloxide dimers [{Me2In(OSiEt3)}2] (1), [{Me2Ga(OSiEt3)}2] (2), [{Me2In(OSi(OtBu)3)}2] (3), [{Me2Ga(OSi(OtBu)3)}2] (4), and In[OSi(OtBu)3)] (5) is reported. Compounds 14 are readily accessible by facile Bronsted reaction of InMe3 or GaMe3 with the corresponding silanols Et3SiOH and (tBuO)3SiOH, respectively. Compound 5 could be obtained by analogous protolysis of [In{N(SiMe3)2}3] with an excess amount of (tBuO)3SiOH. The suitability of 15 to serve as molecular precursors for low-temperature synthesis of amorphous indium and gallium oxide for electronic applications was probed. Thus their thermal degradation was studied by Thermogravimetric/differential thermogravimetry analysis (TGA/DTG). Compounds 14 were decomposed under dry synthetic air (20?% O2, 80?% N2) at low temperature to yield amorphous indium oxide and gallium oxide particles, respectively. In contrast, thermal degradation of 5 affords amorphous indium silicate. All of these products were analyzed by multiple techniques including powder X-ray diffraction analysis (PXRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). Thin-film field-effect transistors (FETs) could be fabricated through spin-coating of silicon-wafers with solutions of 1 in toluene and subsequent calcination under dry synthetic air at 350 degrees C. These films exhibit very good FET performance with a field-effect mobility of 3.0 x 10-1 cm2?V-1?s and an on/off current ratio of 108.