Abstract
Fourier transform infrared (FTIR) spectroscopy has proven to be an effective tool for the analysis of OMVPE growth. Both transmission and attenuated total reflection (ATR) provide information including identification and the relative concentrations of both reactants and products. Until recently we have only been able to apply transmission to the gas phase and ATR to in situ surface analysis. OMVPE is a heterogeneous process and ATR using a GaAs element is limited to temperatures where the sample is transparent,i.e. <400° C. Surface reactions are important to the overall process. We have recently developed a technique which effectively monitors the surface species in situ. All materials emit infrared radiation proportional toT 4. Under OMVPE growth conditions (400-70° C) this emission is considerable, particularly from the surface of the emitting sample. Emission spectra correspond directly to that of absorption spectra and can easily be collected with an FTIR spectrometer. The spectra yield the same information as transmission FTIR primarily for surface species. We have used this system to monitor the adsorption and reaction of TMGa and ammonia. We have identified adsorbed ammonia and TMGa on the surface and have been able to see how these molecules change as they decompose on the surface.
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