Electromodulation spectroscopy of the ground and excited state transitions in GaInN/AlInN multi-quantum wells

Abstract

Contactless electroreflectance (CER) has been applied to investigate energies and intensities of optical transitions in GaInN/AlInN multi-quantum wells (MQWs) with the various QW widths (1.55 and 1.8 nm) and barrier thicknesses (3 and 6 nm). In addition to the ground state transition, optical transitions related to excited states (2H–1C and 1H–2C transitions, where kH– lC denotes a transition between the kth valence and the lth conduction subbands) have been observed in CER spectra. It has been found that the intensities of 2H–1C and 1H–2C transitions (i.e., transitions which are forbidden for non-polar square-like QWs) are comparable with the intensity of the ground state transition. In addition, it has been observed that the relative intensities of QW transitions depend on both the QW width as well as the barrier thickness. This experimental observation has been confirmed by theoretical calculations performed in the framework of the electron effective mass approximation model taking into account polarization effects in wurtzite III-N alloys. The calculations clearly show that the intensity of QW transitions for GaInN/AlInN MQWs strongly varies with the QW width as well as the barrier thickness.