Breakdown of optical selection rules in a highly biased quantum well

Optical transitions between electronic states in a quantum well are governed by symmetry of the states. The selection rule and its breakdown in electric fields have been intensively studied. However, most of such studies have concerned with ground states so far. Behavior of transitions between higher states in high electric fields has not been well revealed. In this paper, in order to investigate optical transitions of high-index states in electric fields, we carried out electroreflectance measurement for a quantum well embedded in a p–i–n diode. Measured electroreflectance spectra are rich in structure, indicating that many transitions between high-index states occur. With increasing applied voltage, these signals show significant red-shift as well as modulation of intensity. We show that the modulation of intensities is well understood from shapes of the wave functions and their deformation due to applied electric field.