Nonradiative investigation of hole photoionization spectrum of EL2 in carbon concentration controlled semi-insulating GaAs

Piezoelectric photoacoustic (PPA) measurements were carried out before and after secondary light illumination to investigate EL2 in carbon concentration controlled semi-insulating (SI) GaAs. The PPA spectra before secondary light illumination show a broad peak around 0.95 eV and a hump up to the band gap energy and are attributed to hole and electron photoionizations of EL2, respectively. The photoionization spectra of EL2 were obtained from PPA measurements. We also found that the hole photoionization of EL2 is not influenced by secondary light illumination even after a long period of illumination.