Electron and hole trap levels in semi-insulating GaAs investigated by a temperature variation of piezoelectric photo-thermal spectra

Temperature variation of the piezoelectric photo-thermal (PPT) spectra of semi-insulating (SI) GaAs from 15 K to room temperature was measured. Curve fitting procedure was carried out for the experimental results in terms of a theoretical analysis based on rate equations for electrons in conduction band (CB) having regard to deep levels. We identified that the observed peaks were due to the nonradiative electron transitions into the deep electron trap levels. By changing the wavelength of an excitation light, new peaks were observed. Considering a photo-ionization cross section spectra for electrons and holes in GaAs, these peaks are considered due to hole traps.