Optical isothermal capacitance transient spectroscopy was used to characterize prominent mid-gap carrier traps in Si-doped n-type samples which had been grown by means of metal-organic vapor-phase epitaxy. Strong carrier photo-ionization was detected from 2 deep levels to the conduction band. The first level photo-ionized over a broad range, from below 1.8 to over 2.3eV. It was seen in all n-type material, was believed to be defect-related and to be involved in yellow luminescence. The second and more dominant peak developed with an incident photon energy of about 2.3eV. This was a previously unreported and unidentified impurity-related level.

P.Hacke, H.Okushi: Applied Physics Letters, 1997, 71[4], 524-6