Assessment of persistent-photoconductivity centers in MBE grown Al _x Ga_1-x as using capacitance spectroscopy measurements

Abstract

Deep-level transient spectroscopy and thermally stimulated capacitance measurements were used to investigate the properties of deep traps in Si-dopedn-Al _x Ga_1−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.