InGaN/GaN multiple quantum wells (MQWs) were grown on (0001) sapphire substrates, which were first coated with thick GaN or AIN films, at relatively low temperatures (650 degrees C). At this growth temperature, we found by x-ray diffraction that the MQWs show distinct higher order superlattice peaks, indicating that the interfaces between wells and barriers are abrupt with little interdiffusion between the layers. However, photoluminescence and cathodoluminescence studies provide evidence that at such low growth temperatures, the inhomogeneities in the InGaN alloys are enhanced due to spinodal decomposition in these alloys.