Observation of photoinduced intersubband transitions in one-dimensional semiconductor quantum wires

We report on midinfrared intersubband transitions between the quantized lev els of undoped GaAs/AlxGa1-xAs quantum wires that are grown on nonplanar su bstrates. Using photoinduced infrared absorption spectroscopy, we were able to resolve two absorption lines in the 120-160 meV range. The first absorp tion line follows the polarization selection rules for intersubband transit ions and exhibits photoinduced excitation profile that resembles the photol uminescence excitation spectrum of the quantum wires. The second absorption resonance, at a higher energy, is not polarized and resembles the photolum inescence spectrum of the side quantum wells. Based on these results and en ergy level calculations, we assign the first absorption resonance to inters ubband transition between the quantized subbands of the quantum wires. The origin of the second resonance is less clear. We propose a model that attri butes this resonance to an interface localized exciton mode that arises fro m interface roughness of the side quantum wells and the wires.