AVS 50th International Symposium
    Semiconductors Tuesday Sessions
       Session SC-TuA

Paper SC-TuA1
Complex Formation between Magnesocene (MgCp@sub 2@) and NH@sub 3@: Origin of the "Memory Effect"

Tuesday, November 4, 2003, 2:00 pm, Room 321/322

Session: Compound Semiconductor Growth and Processing
Presenter: G.T. Wang, Sandia National Laboratories
Authors: G.T. Wang, Sandia National Laboratories
J.R. Creighton, Sandia National Laboratories
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Magnesocene (MgCp@sub 2@) is a common Mg precursor for the p-type doping of Group III nitride semiconductor materials. Unfortunately, difficulties remain with controlling the incorporation of Mg during MOCVD film growth, which often exhibits poorly understood memory effects. While the formation of a reaction product between magnesocene and ammonia has been previously speculated, one has never been experimentally isolated or identified. We have spectroscopically observed and identified, for the first time, the adducts formed between magnesocene and ammonia. Density functional theory (DFT) quantum chemistry calculations have also been performed on the system to determine the structures and energetics of the reaction products. It was found that ammonia can form complexes with magnesocene in both 1:1 and 2:1 ratios, i.e. NH@sub 3@:MgCp@sub 2@ and 2NH@sub 3@:MgCp@sub 2@, via NH@sub 3@ attack of the positively charged Mg center of MgCp@sub 2@. Adduct formation is reversible and the 1:1 and 2:1 products can be converted to one another by varying the NH@sub 3@ partial pressure. Both adducts are condensable at room temperature and their formation is the probable origin of the magnesium memory effects that have been observed during MOCVD of III-Nitride materials. Improved understanding of the equilibrium between condensed phase adducts, gas phase adducts, and precursors should allow for reactor and processing adjustments that reduce or eliminate the memory effects. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.