Deep electronic levels of Al x Ga1-x N (0.25<x<0.60) were investigated by deep level transient spectroscopy (DLTS) and photocapacitance methods. Si-doped AlGaN layers were grown on an AlN/sapphire template by metal–organic vapor phase epitaxy. DLTS analysis using a sampling time window of up to 100 s showed two dominant deep levels with activation energies (ΔE) higher than 1.0 eV in Al x Ga1-x N with x=0.25 and 0.37. The densities of those levels were higher than 1×1016 cm-3. For the Al0.60Ga0.40N sample, the deeper levels (ΔE>1.5 eV) were detected by photocapacitance measurement. It was found that the energy position of the dominant deep level closely followed the Fermi level stabilization energy reported by Walukiewicz et al. [J. Cryst. Growth 269 (2004) 119], indicating that the origin of the dominant deep level in AlGaN is related to a defect complex including anti-site defects and divacancies.

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