V3+ centres in GaAs and GaP: an ENDOR investigation
V3+ impurity centres in GaAs and GaP were investigated with electron nuclear double resonance (ENDOR) spectroscopy. The hyperfine interactions with the 51V impurity nucleus and several shells of As, P and Ga neighbours as well as quadrupole interactions could be determined accurately. An undistorted tetrahedral symmetry was found for V3+ in both crystals. The electron spin is S=1. From the interpretation of the hyperfine and quadrupole data it is concluded that V3+ is on a substitutional Ga site. A reinterpretation of published EPR/ENDOR data on Fe3+ centres in GaAs and GaP shows that also Fe3+ is on a substitutional Ga site and not interstitial as claimed previously. The distribution and localisation of unpaired spin density is discussed and compared with theoretical expectations.