Properties of MOCVD GaN/AlGaN heterostructures grown on polar and non-polar bulk GaN substrates

In this work we present structural, optical and electrical properties of GaN epilayers and AlGaN/GaN MOCVD heterostructures obtained on polar and non-polar 10x10 mm(2), 1 and 1.5 inch bulk ammonothermal GaN substrates. The results were obtained based not only on a single-point measurement but also on mapping across the sample area. In contactless electroreflectance (CER) spectra CER resonances related to optical transitions between excited states were clearly observed for GaN/AlGaN QWs grown on c-plane GaN substrates, whereas such features were not noted in the case of GaN/AlGaN QWs grown on m-plane GaN substrates. This experimental result clearly shows that the polarization-related electric field leads to the quantum confinement of some extra states in the polar QW system. To check the advantage of homo-epitaxy using ammonothermal GaN, high electron mobility transistors (HEMTs), and light emitting diodes (LEDs) structures were grown on (0001) Ga-polarity, semi-insulating and conductive GaN substrates respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim