The identification of species evolved in the evaporation of III-V compounds

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Abstract
Methods are discussed for distinguishing between volatile species in a direct evaporation flux from those produced by various background interactions, using mass-spectrometric techniques. It is shown that while flux modulation methods are essential, phase-sensitive detection at a single frequency is inadequate, and that measurements must be made over a wide frequency range. The improvement over frequency domain methods which can be achieved using time representation of the pulsed signal with signal-averaging and fast Fourier transforms is illustrated. In addition, a means of minimizing mass discrimination effects in the mass spectrometer is described. Results obtained by the application of various forms of data acquisition and signal processing to the Knudsen and Langmuir evaporation of InP, GaP and GaAs are presented, and some thermodynamic implications of the new vapour pressure values examined.