InxGa1-xN/GaN quantum well (QW) Structures grown on c-plane and m-plane surfaces have been investigated intended for long wavelength light emitters. On c-plane InxGa1-xN QWs reached indium concentrations of x(ln) >= 35% with good optical and structural quality. For QW thicknesses d(QW)<= 2 nm a fully strained layer structure is observed and the indium concentration is quite homogenous. Under the same growth conditions of the QW region we find similar or even slightly larger indium concentrations on m-plane surfaces. QWs of such high indium concentrations, however, are very sensitive to the growth conditions of the subsequent layers and we observe degradation such as indium outdiffusion or partial relaxation for high growth temperatures. (C) 2008 Elsevier B.V. All rights reserved.