High quality, high efficiency and ultrahigh In-content InGaN QWs – the problem of thermal stability

InxGa1-xN/GaN quantum well (QW) structures with Indium concentrations above 30% suited for light emitters in the green and beyond have been investigated. The structures were optimized for homogeneous Indium distributions and abrupt interfaces. We obtained very high internal quantum efficiencies (IQE) of 80% and 70% for 460 nm and 510 nm emission wavelength, respectively. However, for high In concentrations the heterostructures are thermally less stable. This is evident from systematic studies including varied GaN cap temperatures and different post annealing procedures. For elevated temperatures we observe a reduction of the PL intensity, a broadening and a shift to higher energies of the PL lines without indication of phase separation. The reason is the soft indium-nitrogen bond, the degradation likely occurs by In interdiffusion or outdiffusion via defects in the structures. The critical temperatures are well below those typical for p-GaN contact layer growth and thus need to be considered in device applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)