INVESTIGATIONS OF UNDOPED AND MG-DOPED WURTZITE GAN WITH LUMINESCENCE-DETECTED PARAMAGNETIC-RESONANCE IN THE 4 MM BAND

Nominally undoped and Mg-doped wurtzite GaN grown with MOVPE on sapphi re substrates were investigated with photoluminescence-detected electr on paramagnetic resonance (PL-EPR). For enhanced resolution a microwav e frequency of 72 GHz (V-band) was used. PL-EPR was measured via the y ellow 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 degrees C in N-2. In undoped GaN a new isotropic donor-like res onance with g = 1.958 was detected which is usually hidden underneath two dominant and well-known signals attributed to a residual shallow d onor and a deep defect when using K- or Q-band microwave sources (appr ox. 24 and 36 GHz, respectively). This observation indicates that the yellow luminescence is caused by recombination processes where at leas t two different donors are involved. In the different Mg-doped samples three resonances were observed probably due to different Mg-related d efects. The donor resonances around g(\\) = 1.960 (c-axis) in Mg-doped GaN are different from those measured in nominally undoped material. (C) 1998 Elsevier Science B.V. All rights reserved.