X-ray studies of group III-nitride quantum wells with high quality interfaces

This paper reports an investigation of a variety of (InGa)N/GaN multi-quantum-well (MQW) samples grown by metalorganic vapor phase epitaxy on sapphire substrates. Dynamical scattering theory has been used to simulate the x-ray diffraction profiles so as to model the structures and to assess the quality of the grown interfaces. There is good agreement between the theoretical predictions and the experimental data. A systematic comparison of a set of ten-period MQWs with different well widths is also reported together with a discussion of the comparison between a single quantum well (QW) with five- and ten-period MQWs all with the same well and barrier widths and alloy composition. The well and barrier widths deduced from the x-ray measurements agree within experimental error with those predicted from the growth parameters, however, the In content of the wells appears to be substantially lower than that expected. This is discussed in terms of a carbon incorporation model. In the better samples, the (InGa)N/GaN interface is good to within a few monolayers—this is comparable with the best that can be achieved in (AlGa)As/GaAs QWs.