Thermal detection of electron spin resonance in the persistent photoconductive state of semi-insulating GaAs crystals grown from pyrolytic BN crucibles

Thermally detected electron spin resonance (TDESR) has been applied to paramagnetic defects characteristic of semi-insulating (SI) GaAs crystals grown from pyrolytic boron nitride (pBN) crucibles. A strong isotropic TDESR signal near g=2.2 and two anisotropic lines at higher fields were observed at T=4.2 K and 13 GHz after in situ optical excitation. Spin-dependent scattering of electrons, in their persistent photoconducting state, by paramagnetic defects is discussed as a possible cause of these resonances. Unsuccessful searches for this TDESR signal in semi-insulating GaAs crystals grown under non-pBN ambient conditions point to paramagnetic defects owing to the inclusion of some crucible material, e.g., nitrogen, as the source of the TDESR spectrum in pBN-GaAs.