The first substituent‐induced “flip” from p‐ to n‐type conductivity as well as enhanced thermal stability and volatility are found for fluorocarbon‐functionalized sexithiophene 1 (relative to the fluorine‐free analogues 2 and 3). Evaporated films of 1 behave as n‐type semiconductors, and can be used to fabricate thin‐film transistors with field‐effect mobilities as high as 0.02 cm2 V−1 s−1—some of the highest reported to date for n‐type organic semiconductors.

The growth and properties of transparent conducting oxides (TCOs) have recently been the subject of intense academic and industrial investigation. [1] This reflects a plethora of technologically important TCO applications ranging from photovoltaic (PV) cells to flat-panel displays and organic light-emitting diodes. While tin-doped indium oxide (ITO) has been heavily studied as the TCO layer for a variety of opto-electronic applications (including transparent electrodes for PVs), [1] and reports have documented the growth of ITO films via numerous techniques, ITO is not ideally suited for use in future PV systems. Reasons include less than optimum conductivity and transparency, high cost, and cation diffusion between ITO and the Cd chalcogenide PV-active layers. [2] To address this problem, thin films of the Cd-containing TCO, cadmium stannate (Cd 2 SnO 4 ), have recently been grown by rf sputtering. [3] These films exhibit promising electrical and optical properties, including a high carrier mobility (59.6 cm 2 V ±1 s ±1 ). [3] However, the lack of suitable Cd precursors has so far impeded the growth of Cd 2 SnO 4 , or any other Cd-based TCO thin film grown by efficient CVD techniques. Thin films of the parent TCO, CdO, have been extensively studied and are known to be highly conductive, primarily due to various defect structures. While CdO has a modest intrinsic bandgap (~2.3 eV), [4] it serves as an excellent model material for the development of TCO CVD processes. Furthermore, previous work in this laboratory and elsewhere has shown that n-type aliovalent doping of CdO has profound effects on the electronic structure, significantly enhancing both the conductivity and the bandgap by introducing n-type charge carriers [5±8] and therefore blueshifting the band edge via a Burstein±Moss shift. [5,6,9] Metal±organic (MO) CVD is a widely used film growth process which complements physical vapor deposition techniques such as rf sputtering, and certain characteristics of MOCVD are particularly attractive for TCO thin film growth. Growth conditions are closer to ambient, growth at higher O 2 partial pressures is possible, conformal coverage over complex three-dimensional features can be achieved, and the process is amenable to very large-scale depositions. All these attractions afford a technique engineered for maximum overall growth efficiency and diverse applications. However, a crucial feature for a useful MOCVD growth process is the necessity of highly volatile, thermally stable, easy to handle, metal±organic precursors. Such precursors must decompose cleanly at the substrate surface during film growth since premature decomposition causes involatile metal species that remain in the precursor reservoir, while complexes that are too thermally stable decompose incompletely, thereby contaminating the reactor and resultant films.To date, growth of Cd-containing films via MOCVD has only been achieved using dimethylcadmium (CdMe 2 ) or its derivatives as precursors. While CdMe 2 can be used for the growth of the heavier C...

Indium–zinc oxide films (ZnxInyOx+1.5y), with x/y=0.08–12.0, are grown by low-pressure metal-organic chemical vapor deposition using the volatile metal–organic precursors In(TMHD)3 and Zn(TMHD)2 (TMHD=2,2,6,6–tetramethyl–3,5–heptanedionato). Films are smooth (rms roughness=40–50 Å) with complex microstructures which vary with composition. The highest conductivity is found at x/y=0.33, with σ=1000 S/cm (n-type; carrier density=3.7×1020 cm3; mobility=18.6 cm2/V s; dσ/dT<0). The optical transmission window of such films is broader than Sn-doped In2O3, and the absolute transparency rivals or exceeds that of the most transparent conductive oxides. X-ray diffraction, high resolution transmission electron microscopy, microdiffraction, and high resolution energy dispersive X-ray analysis show that such films are composed of a layered ZnkIn2O3+k phase precipitated in a cubic In2O3:Zn matrix.

A new class of volatile, low-melting, fluorine-free lanthanide metal-organic chemical vapor deposition (MOCVD) precursors has been developed. The neutral, monomeric Ce, Nd, Gd, and Er complexes are coordinatively saturated by a versatile, multidentate ether-functionalized beta-ketoiminato ligand series, the melting point and volatility characteristics of which can be tuned by altering the alkyl substituents on the keto, imino, and ether sites of the ligand. Direct comparison with conventional lanthanide beta-diketonate complexes reveals that the present precursor class is a superior choice for lanthanide oxide MOCVD. Epitaxial CeO(2) buffer layer films can be grown on (001) YSZ substrates by MOCVD at significantly lower temperatures (450-650 degrees C) than previously possible by using one of the newly developed cerium beta-ketoiminate precursors. Films deposited at 540 degrees C have good out-of-plane (Deltaomega = 0.85 degrees ) and in-plane (Deltaphi = 1.65 degrees ) alignment and smooth surfaces (rms roughness approximately 4.3 A). The film growth rate decreases and the films tend to be smoother as the deposition temperature is increased. High-quality yttrium barium copper oxide (YBCO) films grown on these CeO(2) buffer layers by pulsed organometallic molecular beam epitaxy exhibit very good electrical transport properties (T(c) = 86.5 K, J(c) = 1.08 x 10(6) A/cm(2) at 77.4 K).