Modification of the Magnetic and Electronic Properties of Ordered Arrays of (II, Mn)VI Quantum Wires Due to Reduced Lateral Dimensions

Abstract

We present a novel way of synthesising highly ordered arrays of Cd1—xMnxS and Cd1—xMnxSe quantum wires with lateral dimensions of 3 nm separated by 2 nm SiO2 barriers by incorporating the (II, Mn)VI semiconductor with 0 ≤ x ≤ 1 into the pore system of mesoporous MCM-41 SiO2 matrices. The electronic and excitonic properties were studied using photoluminescence and photoluminescence excitation spectroscopy at low temperatures and in magnetic fields up to 7.5 T. Due to the quantum confinement of the excitons in the wires an increase of the direct band gap by about 200 meV for (Cd, Mn)S and by about 350 meV for (Cd, Mn)Se is observed. In addition, we observe a much stronger, p–d hybridisation related band gap bowing as a function of Mn-concentration in the wires compared to bulk. This effect is related to the increase of the band gap due to the quantum confinement which shifts the p-like valence band edge closer to the Mn-3d-related states in the valence band. Surprisingly, the s,p–d exchange induced giant Zeeman splitting of the excitons in the (Cd, Mn)Se wires compared to those in bulk material appears to be very small. The magnetic properties of the samples were studied by SQUID and electron paramagnetic resonance measurements in the temperature range from 2 to 300 K. Compared to the bulk (II, Mn)VI compounds, a reduced antiferromagnetic coupling between the magnetic moments of the Mn2+ ions is found. For x > 0.8, a suppression of the paramagnetic to antiferromagnetic phase transition of the Mn-system is observed because the lateral dimensions of the wires are smaller than the magnetic length scale of the antiferromagnetic ordering.