Investigations of undoped and Mg-doped wurtzite GaN with luminescence-detected paramagnetic resonance in the 4 mm band

Abstract

Nominally undoped and Mg-doped wurtzite GaN grown with MOVPE on sapphire substrates were investigated with photoluminescence-detected electron paramagnetic resonance (PL-EPR). For enhanced resolution a microwave frequency of 72GHz (V-band) was used. PL-EPR was measured via the yellow luminescence in undoped and via the blue Mg-related luminescence in Mg-doped samples. The Mg-doped samples were as-grown and annealed at 650°C in N2. In undoped GaN a new isotropic donor-like resonance with g=1.958 was detected which is usually hidden underneath two dominant and well-known signals attributed to a residual shallow donor and a deep defect when using K- or Q-band microwave sources (approx. 24 and 36 GHz, respectively). This observation indicates that the yellow luminescence is caused by recombination processes where at least two different donors are involved. In the different Mg-doped samples three resonances were observed probably due to different Mg-related defects. The donor resonances around g‖=1.960 (c-axis) in Mg-doped GaN are different from those measured in nominally undoped material.