IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC-MoA

Paper SC-MoA7
Search for the Missing Group-III Flux during AlGaN OMVPE

Monday, October 29, 2001, 4:00 pm, Room 124

Session: GaN Surfaces, Interfaces, and Devices
Presenter: J.R. Creighton, Sandia National Laboratories
Authors: J.R. Creighton, Sandia National Laboratories
M.E. Coltrin, Sandia National Laboratories
R.P. Pawlowski, Sandia National Laboratories
Correspondent: Click to Email
At normal operating conditions, most AlGaN OMVPE reactors exhibit non-ideal behavior with respect to the group-III precursor concentration. The deposition rate can be considerably less than the predicted transport-limited rate, and the solid AlGaN alloy composition is typically a nonlinear function of the gas-phase composition. It is generally thought that gas-phase "parasitic" reactions between trimethylgallium (TMGa), trimethylaluminum (TMAl), and ammonia are responsible for removing group-III material from the deposition process. We have explored many possible mechanisms for the parasitic pathways using both experimental techniques and complex reactive flow simulations. As expected, TMGa and TMAl react with ammonia to form adducts, which we have unambiguously identified with mass spectroscopy and FTIR. We have measured the vapor pressure of the adducts and their mixtures near room temperature and found that physical condensation can be an important process, especially at higher reactor pressures and higher TMAl concentrations. However, over the 0-100°C range we have found no evidence of significant irreversible decomposition reactions, such as methane elimination, which have often been postulated to be the source of the decrease in group-III flux. As the temperature is raised in this range, the adducts simply dissociate back into the original reactants at rates consistent with equilibrium calculations. The lack of evidence for a low temperature parasitic reaction pathway is consistent with our reactive flow simulations, which indicate that the parasitic reaction pathway occurs at high temperatures near the growing surface. The simulations utilized deposition rate measurements from a rotating disk reactor over a wide range of operating conditions chosen to accentuate the differences between possible high-temperature and low-temperature pathways. Recent results examining possible high-temperature pathways will be presented.