Ah Cowley

Direct evidence for the β-hydride elimination mechanism in the decomposition of triethylgallium on GaAs(100)

Abstract Decomposition of the surface ethyl group formed by dissociative adsorption of triethylgallium (TEGa) on GaAs(100) is investigated using temperature programmed desorption. Deuterium labeling indicates that decomposition of the surface ethyl group proceeds exclusively through a β-hydride elimination reaction mechanism without any scrambling between α- and β-hydrogens. For undeuterated TEGa (TEGa-d0), the surface ethyl group decomposes and desorbs simultaneously as C2H4 and H2 at 600 K. For perdeuterated TEGa (TEGa-d15), the desorption of C2D4 and D2 occurs at a slightly higher temperature (630 K). Partially deuterated TEGa (TEGa-d6), with deuterium on the α-carbons, results in H2 and C2H2D2 as desorption products at 600 K. A kinetic isotope effect of 8 ± 5 kJ mol−1 for hydride versus deuteride transfer is determined, which is consistent with cleavage of the CβH bond in the transition state, and with tunneling.

Homolysis versus β-hydride elimination in the decomposition of trialkylgallium on GaAs(100)

Abstract The decomposition of various surface alkyl groups on GaAs(100), which were generated by dissociative adsorption of the corresponding trialkylgallium precursors R 3 Ga (R=Me, Et, Et- d 5 , n Pr , i Pr , n Bu and t Bu ), was studied by temperature programmed desorption. Two elimination pathways were observed, homolysis and β-hydride elimination. The former reaction results in the formation of alkyl radicals and the latter gives alkene and H 2 as products. On GaAs(100), both reactions are observed in the decomposition of all surface alkyl groups, except for methyl that reacts by homolysis. For each surface alkyl group, homolysis always occurs at slightly lower temperature than β-hydride elimination. Experiments with perdeuterated triethylgallium reveal that surface Et groups do not undergo coupling with coadsorbed deuterium on the surface to form ethane, and that ethane forms in subsequent wall reactions that involve Et radicals. The activation energy E a for homolysis followed the trend Me>Et> n Pr> n Bu> i Pr> t Bu , which reflects the strength of alkyl–surface bonds as well as the increased stability of the alkyl radical. The E a for β-hydride elimination follows closely the E a for homolysis and exhibits similar behavior in terms of magnitude and trend, i.e. Et> n Pr> n Bu≈ i Pr> t Bu , suggesting that breaking the alkyl–surface bond contributes to the activation energy for both homolysis and β-hydride elimination reactions. The alkyl–surface bond energy (Δ H h ) and the heat of reaction for β-hydride elimination (Δ H β ) for all surface alkyls are calculated from the desorption temperatures of their products.

A New Single Source Precursor Approach to Gallium and Aluminum Nitride

Single source precursors which contain preformed gallium-nitrogen and aluminum-nitrogen bonds are being considered for the growth of gallium and aluminum nitride because of their potential for overcoming problems associated with conventional precursors. Presented is the evaluation of dimethylgallium azide, Me 2 GaN 3 (1) , bisdimethylamidogallium azide, (Me 2 N) 2 GaN 3 (2) , and bisdimethylamidoaluminum azide, (Me 2 N) 2 AlN 3 (3) as potential precursors for A1N and GaN film growth. The compounds were evaluated for stability, ease of transport, temperature of decomposition and quality of film deposited. Amorphous thin films of GaN with a band gap of 3.4 eV were deposited with 2 at 250 °C. Increasing the substrate temperature to 580 °C resulted in the deposition of epitaxial GaN films. Polycrystalline A1N films were grown with 3 at 600 °C.