Identification of hole traps in semi-insulating GaAs by means of the temperature-dependent piezoelectric photo-thermal measurements

Temperature dependence of the piezoelectric photo-thermal (P1PT) signal was measured to study the physical parameters of hole traps such as an activation energy, a concentration, and a capture cross section in semi-insulating GaAs. Since the electron and hole optical ionization spectra of EL2 have peaks at different photon energies, the wavelength of the probing light was set at 1240 nm for selectively generating free hole carries from EL2 centers. Four peaks at 40, 65, 90, and 155 K were observed. From the theoretical analysis based on the rate equations of free holes in the valence band and the relevant trap levels, four kinds of hole traps were characterized. Higher temperature peaks at 90 and 155 K are well identified as non-radiative hole transitions through so-called HL12 and HL15, respectively.