Intersubband transitions in coupled wells with disorder

Abstract

Disorder due to doping or interface roughness in quasi-two-dimensional systems causes in-plane localization of the electrons and strongly affects their optical properties. We present numerical calculations of intersubband (IS) emission spectra for the case of a doped double-quantum-well, including disorder localization by an exact diagonalization method. It is demonstrated that the inhomogeneous line broadening of the IS peak is then determined by an interplay of correlation-effects in the single-particle spectrum and the spatially indirect nature of the IS inter-well transitions. The resulting line width is larger than in the case of intra-well transitions, but still considerably smaller than the typical fluctuations of the effective random potential. We further show how the energy selective tunneling injection of electrons into the upper subband of a coupled-well structure and the observation of the IS luminescence spectrum can yield valuable information about the physics of localization in multi-subband systems.