Defect studies with positrons: what could we learn on III-nitride heterostructures?

We have applied positron annihilation spectroscopy to study 400 – 500 nm InGaN-based LED structures, as well as InGaN and AlGaN materials with varying In and Al contents. We find that the effect of adding In to GaN on the annihilation parameters obeys the Vegard's law, while in the case of AlGaN the possible effect of Al is completely screened by efficient formation of cation vacancies. The results obtained in the InGaN LED structures are indistinguishable from defect-free GaN, suggesting that the positrons annihilate preferentially in the barriers of the MQW system.