Gallium hydride complexes stabilised by multidentate alkoxide ligands: precursors to thin films of Ga2O3 at low temperatures.
The donor-functionalised alkoxides {Me(3-x)N(CH(2)CH(2)O)(x)} (L(x); x = 1, 2) have been used to form gallium hydride complexes [{GaH(2)(L(1))}(2)] and [{GaH(L(2))}(2)] that are stable and isolable at room temperature. Along with a heteroleptic gallium tris(alkoxide) complex [Ga(L(1))(3)] and the dimeric complex [{GaMe(L(2))}(2)], these compounds have been used as single-source precursors for the deposition of Ga(2)O(3) by aerosol-assisted chemical vapour deposition (AACVD) with toluene as solvent. The resulting films were mostly transparent, indicating low levels of carbon contamination, and they were also mainly amorphous. However, [Ga(L(1))(3)] did contain visibly crystalline material deposited at a substrate temperature of 450 °C, by far the lowest ever observed for the CVD of gallium oxide.
Precursor Chemistry – Main Group Metal Oxides
This chapter describes precursor complexes that have been utilized to deposit thin films of main-group metal oxides. An overview of the wide range of precursors that have been reported for the growth of these oxides, which includes metal alkoxides and β-diketonates, is presented including synthetic details. A number of techniques have been used to deposit the metal oxide films, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), and sol–gel, and the technique employed is described. The focus of the chapter is on the chemistry of precursors to the thin films, although mention has also been made of techniques (such as ALD), which tend to utilize simple, commercially available precursors in combination with a secondary oxygen source. The first section describes precursors for the deposition of aluminum oxide, gallium oxide, and indium oxide. Group 13 oxides have a fascinating range of chemistry and find application as components of high-temperature superconductors, transparent conducting oxides (TCOs), and gas sensors. These applications tend to use doped-group 13 metal oxides, and precursors to these materials have been highlighted at the end of the section. The second section describes the range of precursors that have been used for the formation of group 14 oxide thin films. These materials find application in everyday life from silicon dioxide, or silica, which is widely used in electronics manufacturing, to tin dioxide that is commonly used for gas sensors as well as TCO applications. These oxides have been deposited using a variety of methods that can alter the final properties of the films. In most cases, commercially available precursors have been employed, for example, tin halides and organotin precursors for SnO 2 , with the addition of an oxygen source (usually H 2 O, H 2 O 2 , O 2 , and O 3 ); however, there are a few reported examples of more sophisticated precursors which are described as well as a brief overview of doped-group 14 metal oxides. The last section gives an overview of the precursors developed for the deposition of group 15 and 16 metal oxides – including antimony oxide, bismuth oxide, and tellurium oxide. Thin films of the binary group 15 and 16 oxides have limited applications in comparison to the corresponding group 13 and 14 oxides, for example, antimony oxide finds use in catalysis and gas sensor devices and bismuth oxide are of interest in high T c superconductors and potentially for fuel cells.
Dimethylaluminum and gallium amino alkoxides
Dimethylaluminum and gallium alkoxides of the type Me 2 MOR * were synthesized (M = Al; R = CH(CH 3 )CH 2 NMe 2 ( 1 ), CH(CH 3 )CH 2 NH 2 ( 2 ), M = Ga; R = CH(CH 3 )CH 2 NMe 2 ( 3 )) by reaction of Me 3 M (M = Al; Ga) with the corresponding amino alcohols. The resulting compounds 1–3 have been characterised by 1 H, 13 C and 27 Al NMR spectroscopy. The crystal structures of 1–3 were determined by X-ray diffraction. Compounds 1–3 were proved to be dimeric in solid state containing five-membered heterocyclic rings. 3 crystallises in the monoclinic space group P2 1 / n with Z = 4, a = 7.898( 2 ), b = 15.512(9), c = 8.453(2) A, and β = 103.70(2)°, V = 1000.1(9) A 3 . The Ga-N distance in 3 runs to 2.525(2) A which is significantly longer than the Al-N distances in the investigated Al compounds 1 and 2 (2.246(2) and 2.172(3) A).