Raman monitoring of selenium decapping and subsequent antimony deposition on MBE-grown ZnSe(100)

Epitaxial layers of ZnSe were grown on GaAs(100) substrates using molecular beam epitaxy at a substrate temperature of 300°C. Immediately after growth the samples were capped with thick layers of amorphous Se as a protection against contamination of the ZnSe surface during the exposure to air, e.g. during transport. Such samples were then investigated using Raman monitoring. This new technique is realised by the combination of a specially designed ultrahigh vacuum (UHV) chamber with a triple Raman spectrometer equipped with multichannel detection. As a result, Raman spectra can be taken on-line and in situ from the sample surface during desorption or deposition processes. While Raman spectra from the capped samples taken at room temperature show only a broad structure centred around 255 cm ^-1 , which is characteristic for amorphous Se, the evolution of Raman spectra during the annealing of the samples indicates the formation of crystalline Se for temperatures above 100°C, as can be judged from the appearance of the well known phonon features of trigonal Se. Further annealing results in the complete desorption of the Se cap. Thereafter Sb was deposited on such clean ZnSe(100) surfaces. The formation of the Sb overlayer was investigated for the first time using Raman monitoring. In this case the on-line technique allows the so called explosive phase transition in the overlayer, i.e. from the amorphous to the crystalline state of Sb, to be observed without interrupting the deposition process.