Low-energy cathodoluminescence and photoluminescence spectroscopy was used to characterize the formation of charge states deep within the ZnSe band gap, and localized near to the ZnSe/GaAs interface. It was noted that these deep levels were a common feature of the ZnSe/GaAs heterostructure, and depended sensitively upon the growth conditions and post-growth annealing treatment. Measurements were made of deep-level formation near to the ZnSe/GaAs interface during post-growth annealing, and of their marked dependence upon the initial epitaxial growth conditions. Electron beam energies of 1 to 2keV were used, together with HeCd and HeNe excitation, in order to obtain emission spectra that were characteristic of the free ZnSe surface, the ZnSe bulk, and the ZnSe/GaAs(100) interface. Annealing under ultra-high vacuum, at temperatures ranging from 300 to 500C, produced a new emission feature at 1.9 to 2.0eV whose intensity increased exponentially with temperature, and had an associated activation energy of 1.10eV. This feature was enhanced or suppressed in structures which had been prepared under Se-rich or Zn-rich growth, respectively, and its intensity could therefore be related to the Zn vacancy concentration or to Ga in-diffusion. It was concluded that these results demonstrated the importance of the local composition in the formation of interface deep-level defects, and their subsequent effects upon luminescence efficiency and hetero-junction stability.

A.D.Raisanen, L.J.Brillson, L.Vanzetti, A.Bonanni, A.Franciosi: Journal of Vacuum Science and Technology B, 1995, 13[4], 1705-10