Raman investigation of CdxZn1-xSe/ZnSe quantum wires: Strain relaxation and excitation profile

CdZnSe/ZnSe quantum wires with two different Cd contents and different wire sizes were investigated by resonance Raman spectroscopy. Depending on the Cd content, the longitudinal optical (LO) phonon signal of the wires shows an asymmetry or a clear separation into two peaks. This separation is cause d by an inhomogeneous strain parallel to the layer plane due to the strain relaxation at the wire edges. Thus, the observed signals can be attributed to LO phonons excited in the center and in the edge of the structures. Furt hermore, high outgoing resonances for the LO overtones (2LO and 3LO) can be observed. For two wire sizes [(a): length L=100 mu m, width W=18 nm; (b): L=49 nm, W=27 nm] excitation profiles of the LO fundamental and of the firs t overtone of Cd0.2Zn0.8Se quantum wires have been recorded. The excitation profiles clearly show structures attributed to the incoming and outgoing r esonances. The intensity ratio 2LO/1LO, which is also a good measure for th e electron-phonon coupling in a system, was determined for various wire siz es. The results point to a decrease of the electron-phonon coupling for dec reasing wire length (transition from wire to dot). (C) 2000 American Instit ute of Physics. [S0021-8979(00)03314-4].