Hetero-epitaxial layers of Si-doped n-type Ga0.88Al0.12N which had been grown by means of metalorganic chemical vapor deposition onto SiC substrates were characterized by using capacitance transient spectroscopy. The use of conventional deep-level transient spectroscopy revealed the presence of a dominant deep level with an activation energy, for electron emission to the conduction band, of 0.61eV. The activation energy of this deep level exhibited a marked field dependence, as deduced from double-correlation deep-level transient spectroscopic data. This indicated the existence of a deep donor level in n-type semiconductors. A deep level was observed, by means of optical deep-level transient spectroscopy, with a threshold energy (for electron photo-emission to the conduction band) of 0.77eV. This appeared to be of identical origin to the predominant deep level that had been detected by using deep-level transient spectroscopy. Two additional deep levels were detected, in the upper half of the band gap of these samples, with threshold energies of 0.83 and 1.01eV.

W.Götz, N.M.Johnson, M.D.Bremser, R.F.Davis: Applied Physics Letters, 1996, 69[16], 2379-82