The preparation of Sb contacts to molecular beam epitaxial ZnSe on GaAs(100) monitored by Raman spectroscopy

Epitaxial layers of ZnSe on GaAs(100) grown by molecular beam epitaxy (MBE) were capped with an amorphous selenium layer in order to protect the ZnSe surface against contamination during exposure to air. After transport the capping layer was removed again under ultrahigh vacuum conditions in a thermal desorption process, which was monitored by Raman spectroscopy. The spectra taken continuously while annealing the sample reveal the crystallization of the amorphous layer and then the complete desorption of Se at about 150°C. Thereafter, Sb was evaporated onto such clean ZnSe surface at room temperature (RT). The formation of the Sb contact was again monitored by Raman spectroscopy. Hereby the explosive phase transition from an initially amorphous to a crystalline Sb overlayer was observed online for the first time. In addition, the Sb desorption process was monitored for annealing up to 280°C. After this process new features occur in the Raman spectra, which are discussed in terms of scattering induced by interface roughening and cluster formation at the interface.