Influence of InN and AlN concentration on the compositional inhomogeneity and formation of InN-rich regions in In_xAl_yGa_1−x−yN

The application of quaternary In _xAl _yGa _{1-x- y}N active regions is a promising path towards high efficiency UVB-light emitting diodes (LEDs). For the utilization of In _xAl _yGa _1-x-yN, detailed knowledge of the interplay between growth parameters, adatom incorporation, optical and structural properties is crucial. We investigated the influence of the trimethylaluminium (TMAl) and trimethylindium (TMIn) flux on the composition and luminescence properties of In _xAl _yGa _1-x-yN layers by multi-mode scanning electron microscopy. We found that varying the molar TMIn flow from 0 to 17.3 μmol min ^-1 led to an InN concentration between 0% and 3.2% and an emission energy between 4.17 and 3.75 eV. The variation of the molar TMAl flow from 3.5 to 35.4 μmol min ^-1 resulted in a AlN composition between 7.8% and 30.7% with an emission energy variation between 3.6 and 4.1 eV. Cathodoluminescence hyperspectral imaging provided evidence for the formation of nanoscale InN-rich regions. Analyzing the emission properties of these InN-rich regions showed that their emission energy is inhomogeneous and varies by ≈150 meV. We provide evidence that the formation of these InN-rich regions is highly dependent on the AlN and InN composition of the layer and that their formation will strongly affect the performance of In _xAl _yGa _1-x-yN LEDs.