Superlattices and Microstructures, Vol. 22, No. 1, 1997 The optical absorption of quantum-well wires S. Glutsch, F. Bechstedt Friedrich-Schiller-Universit¨ at, Institut f ¨ ur Festk¨ orpertheorie und Theoretische Optik, 07743 Jena, Germany D. S. Chemla Department of Physics, University of California at Berkeley and Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, U.S.A. (Received 15 July 1996) The optical absorption of quantum-well wires is studied theoretically. A single quantum- well wire is treated by means of the subband expansion which allows us to classify the optical transitions. The accuracy of this approximation for quantitative predictions is examined. For the first time, optical spectra of quantum-well-wire arrays are calculated, including Coulomb interaction and continuum states. The absorption shows Fano resonances and features of above-barrier excitons. As the band offsets increase, we observe a transition to decoupled quantum-well wires. c  1997 Academic Press Limited Optical properties of quantum-well wires have drawn much attention from both experimentalists [1 – 4] and theorists [5 – 10] in the last decade. Key results are the discovery of the center-of-mass quantization [ 1 ] and the prediction of Fano resonances in the optical absorption [ 7 ]. Much progress in fabrication has been reported recently [3 , 4] , which is an important step towards the extreme one-dimensional limit. Some of the difficulties encountered in the description of quantum wires are: (i) the singularity of the one-dimensional density of states, (ii) the 1/|x |-divergence of the one-dimensional Coulomb potential, and (iii) the wire width, which is, typically, larger than the size of the exciton. In a preceding publication [ 11 ] we analyzed the transition from a quantum well to a quantum-well wire. In this paper we study the influence of the subband coupling on the optical spectrum and the optical absorption of quantum-well-wire arrays for different band offsets. The optical susceptibility for a quantum-well wire is given by χ (1 D) (ω) = |µ| 2 ε 0 1 L  +L/2 −L/2 dy  +L/2 −L/2 dy ′  λ  λ (0, y , y ) ∗ λ (0, y ′ , y ′ ) E λ − ¯ h (ω + i ǫ) , where µ is the dipole matrix element of the allowed optical transition, ε 0 = 8.85419 As/(Vm) is the vacuum dielectric constant, ǫ is the homogeneous line widths, and L is the normalization length across the wire 0749–6036/97/050031 + 04 $25.00/0 sm960342 c  1997 Academic Press Limited