Direct optically detected magnetic resonance observation of a copper centre associated with the green emission in ZnSe

Abstract

The green emission at 530 nm in zinc selenide has been studied by means of optically-detected magnetic resonance (ODMR). Observation of hyperfine structure shows unequivocally that copper ions are involved with the emission. The copper ions lie in C_2v symmetry with g_X=1.951+or-0.004, g_Y=2.214+or-0.004, g_Z=2.042+or-0.004, mod A_X mod -4 cm^-1, mod A_Y mod =(155+or-5)*10^-4 cm^-1 and mod A_Z mod -4 cm^-1, with X, Y and Z respectively parallel to (110), (110) and (001) or equivalent directions. The spectrum is attributed to Cu²⁺ either at the zinc substitutional site or at the interstitial site that is surrounded by four selenium ions. The lowering of the symmetry from T_d to C_2v is attributed to the presence of another ion in an (001) type direction relative to the copper. The results of previous workers suggest that this second ion is itself copper, so that the centre would be a copper-substitutional-copper-interstitial pair. The ODMR results show surprisingly that the emission is due to donor-acceptor recombination, the copper centre acting as a deep acceptor.