FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDY OF PREDEPOSITION REACTIONS IN METALLOORGANIC CHEMICAL VAPOR-DEPOSITION OF GALLIUM NITRIDE .2.

This is the second paper regarding the predeposition reactions that occur during metalloorganic chemical vapor deposition (MOCVD) of gallium nitride (GaN). Studies of the reactions between trimethylgallium (TMGa) and the nitrogen sources ammonia (NH3) and nitrogen trifluoride (NF3) have been reported previously. In the present work, triethylgallium (TEGa) was used as the Ga source, and reactions between TEGa and the nitrogen sources NH3 and NF3 were studied with Fourier transform infrared (FTIR) spectroscopy. Just as for the TMGa + NH3 system, the reaction between TEGa and NH3 went to completion immediately after mixing at room temperature. The resulting mixture of reactants and adduct, TEGa:NH3, was observed in the gas phase via FTIR spectroscopy. Assignments of the IR absorption bands of gaseous TEGa:NH3 were made. The room-temperature vapor pressure of TEGa:NH3 is lower than that of TMGa:NH3, which will inhibit transport of the Ga species to the deposition zone in MOCVD of GaN using TEGa as the Ga source. At 150-degrees-C, chemical equilibrium was established between the gaseous adduct, TEGa:NH3, and unreacted TEGa and NH3. The forward rate constant of this predeposition reaction is 3.12 x 10(-3) Torr-1 s-1, which is less than the value determined for TMGa + NH3 (5.89 x 10(-3) Torr-1 s-1). When either TMGa or TEGa was mixed with NF3, no evidence of gas-phase adduct formation was observed at either room temperature or 150-degrees-C.