Optical in situ quantification of the Arsenic content in GaAsP graded buffer layers for III-V-on-Si tandem absorbers during MOVPE growth

The established approach for integration of direct bandgap III/Vs on silicon utilizes GaAsP graded buffer layers. Here, we study graded GaAsP(001) growth in situ with reflection anisotropy spectroscopy (RAS). With increasing As supply, a characteristic spectral fingerprint of the surface reconstruction shifts towards lower photon energies, which is well observable at growth temperature and for a broad range of As concentrations. Within a simplified empirical model, this shift depends approximately Iinearly on the As content in the GaAsP layer. The As content of individual GaAsP layers can thus be quantified in situ during growth which is beneficial for process control.