Mass spectrometric study of the vapour composition in a hot-wall-reaction tube for CdTe

Abstract

During the past few years epitaxial layers of II–VI compound semiconductors were successfully grown by Hot-Wall Epitaxy (HWE). However, detailed knowledge about the processes in the reactor is rather poor. In order to investigate the gas in the reactor during growth, a Quadrupole-Mass Spectrometer was connected for the first time to the HWE system. We evaporated CdTe from a polycrystalline source and identified the different vapour species by testing the isotope distribution. Cd +, Te 2 + and Te + ions were observed. The Cd- and Te 2-ion currents were monitored as a function of the CdTe-source temperature. From this measurements the equilibrium enthalpy of evaporation was obtained in agreement with literature data. Intensities of Cd + and Te 2 + signals were studied as a function of different temperature profiles in the system. For all thermodynamic conditions investigated we found that the partial pressures are governed by the mass action law. This gives rise to the assumption that it is possible to grow CdTe layers with desired composition.