Interband absorption due to dipole coupling and interference in isolated quantum-wire structures.

Abstract

We present a self-consistent field theory and numerical calculations for a set of temperatures and electron densities for the interband absorption coefficient and the frequency-dependent refractive index for an array of isolated quantum wires. The peaks in the absorption coefficient correspond to interband transitions, resulting in the resonant absorption of light. The peaks in the refractive index are slightly redshifted from those in the absorption coefficient because the former involve both the real and imaginary parts of the response function, whereas the latter is directly proportional to the imaginary part of the response and inversely proportional to the refractive index. There is interference between the real and imaginary parts when the derivative of the absorption coefficient is taken with respect to frequency, which greatly modifies the line shape in the absorption spectrum. The oscillations in the derivative spectrum are due to the quantization of the energy levels related to the in-plane confining potential for such reduced dimensional systems. There are appreciable changes in the absorption spectrum when the electron density or temperature is increased. One interband transition peak is suppressed in the high electron density limit and the thermal depopulation effect on the electron subbands can be easily seen when the temperature is high. We also find that the exciton coupling weakens the shoulder features in the absorption spectrum. This paper is relevant to optical characterization techniques.