An electrically active defect was detected in epitaxial layers of 4H-type material which had been grown by means of vapor-phase epitaxy. This defect was characterized by a level at about 0.70eV below the conduction-band edge, an extrapolated capture cross-section of about 5 x 10-14cm2 and a concentration of approximately 1013/cm3. Secondary-ion mass spectrometry revealed no sign of Ti, V or Cr. After 2MeV electron irradiation, the 0.70eV level did not increase in concentration, but 3 new levels were observed at approximately 0.32, 0.62 and 0.68eV below Ec; with extrapolated capture cross-sections of 4 x 10-14, 4 x 10-14 and 5 x 10-15cm2, respectively. However, the defects which caused these levels were unstable, and decayed after some time at room temperature. This resulted in the formation of the 0.70eV level. The results strongly suggested that the 0.70eV level originated from a defect of intrinsic type. Such an unstable behavior by electron irradiation-induced defects had not been observed in the 6H polytype at room temperature.

J.P.Doyle, M.K.Linnarsson, P.Pellegrino, N.Keskitalo, B.G.Svensson, A.Schöner, N.Nordell, J.L.Lindström: Journal of Applied Physics, 1998, 84[3], 1354-7