Band gap energy fluctuations in InGaN films grown by RF-MBE with changing nitrogen supply rate investigated by a piezoelectric photothermal spectroscopy

In this study, non-radiative recombination center in InGaN films with varying III/N ratio grown by rf-molecular beam epitaxy was investigated directly by piezoelectric photothermal spectroscopy (PPTS). To clarify the influence of the III/N supply ratio during the InGaN layer growth, the nitrogen flow rate was changed from 1.0 to 2.0 sccm. Since metallic-indium droplets and phase separation were observed for the samples grown by low nitrogen flow rate, it was found that these have been grown under a group-III-rich condition. With increasing nitrogen flow rate, the indium content in InGaN films increased. The estimated non-radiative recombination edges determined from PPTS method (PPT edge) red-shifted with increasing the nitrogen flow rate. The energy difference between estimated band edge and the PPT edges increased with increasing flow rate under group-III rich condition, and became saturated under the N-rich condition. It is considered that the existence of the phase separation is related to this behavior. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)