Assessment of persistent-photoconductivity centers in MBE grown Al x Ga1-xas using capacitance spectroscopy measurements
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Deep-level transient spectroscopy and thermally stimulated capacitance measurements were used to investigate the properties of deep traps in Si-dopedn-Al x Ga1−xAl layers grown by molecular beam epitaxy. Two electron traps at electron emission activation energies of 0.44 and 0.57 eV have been detected. Both traps were studied in detail and found to be the origin of the persistent-photo-conductivity phenomenon in this material. The nature of both traps is the same as of the DX center in liquid phase epitaxial material reported by Lang et al. The electron capture cross-sections areσ n 1 =σ n 2=8.3×10−22cm2 atT=205K. Activation energies ofE σ 1= 0.33eV andE σ 2=0.37eV at temperatures higher than 125 K were determined by DLTS measurements and by direct measurements of the capture transient. In order to allow for the variation of the free-electron concentration during the capture process, a new method for the evaluation of the electron capture crosssection was developed.
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