Low Temperature Laser-Assisted Gas Phase Reactivity of TMGa with NH 3 and Oxygen-Containing Compounds (H 2 O, CH 3 OH, O
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Low Temperature Laser-Assisted Gas Phase Reactivity of TMGa with NH3 and Oxygen-Containing Compounds (H2O, CH3OH, O(CH3)2) in Constrained Pulsed Expansions Alexander Demchuk1, Michael Lynch, Steven Simpson and Brent Koplitz Department of Chemistry, Tulane University, New Orleans, LA 70118, U.S.A. 1 APA Optics, Inc., 2950 NE 84th Lane, Blaine, MN 55449, U.S.A. ABSTRACT The present work reports on the study of III-V gas phase reactivity in constrained gas pulse expansions of trimethylgallium (TMGa) and oxygen derivative compounds (H2O, CH3OH, O(CH3)2) with and without ammonia. The precursors are introduced separately into a high vacuum chamber via a multipulsed gas nozzle assembly. The gas mixtures are then exposed to a UV pulse from an ArF excimer laser (λ=193 nm) and the products are mass analyzed with a quadrupole mass spectrometer. The efficient laser-assisted growth of Ga-O-containing clusters in the form of [(CH3)2GaOR]x, where R is H or CH3, has been revealed. Different behavior can be seen in the reaction of TMG and the oxygen species depending on the presence of H atoms bonded to the oxygen. Significant influence of NH3 on cluster formation and oxygen incorporation is demonstrated. INTRODUCTION Previously, we have reported on our efforts to explore low temperature III-V material growth in a gaseous environment by combining UV laser photolysis and the metalorganic chemical vapor deposition (MOCVD) technique using trimethylgallium (or trimethylaluminum) and ammonia as precursors [1-3]. The main gas phase reaction at low temperature in this process is directed by a strong interaction between the metal alkyls and ammonia to form the Lewis acidbase adduct compound (CH3)3M:NH3, where M is Al or Ga [4-8]. Laser irradiation of such gas mixtures with 193-nm photons revealed extensive (CH3)kMl(NH2)m(NH)n cluster formation in the gas phase as a result of photolysis reactions of the precursor and adduct molecules [1-3]. In the current paper, we present recent research the gas phase reactivity of TMGa with the oxygen-containing compounds: H2O, CH3OH and O(CH3)2, as well as ammonia. The reaction of TMGa with these oxygen compounds, especially H2O, can be used to study MOCVD side reactions, as water is a main impurity in commercial ammonia and could thus be a primary source for the oxygen found in nitride films.
EXPERIMENTAL The experimental apparatus consists of a high vacuum chamber equipped with a quadrupole mass spectrometer (QMS) and a specialized pulsed nozzle source that is described elsewhere [1,2]. The TMGa ((CH3)3Ga), ammonia (NH3), and oxygen compounds [water (H2O), methanol (CH3OH), and dimethylether (O(CH3)2)] are introduced into the high vacuum chamber via the nozzle assembly. TMGa is used with Ar as the carrier gas. The water and methanol (liquid in normal conditions) are heated to 100 oC and 60 oC, respectively, and introduced into the mixing
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region under their own vapor pressures. Pulsed flows of each sample gas (TMGa, oxygen compound, and/or NH3) are simultaneously and independently inje
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