Structural and Magnetic Properties of Nitrogen Acceptor Co-doped (Zn,Fe)Te Thin Films Grown in Zn-Rich Condition by Molecular Beam Epitaxy (MBE)

Abstract

We have investigated the structural and magnetic properties of (Zn,Fe)Te:N thin films grown under Zn-rich condition with Fe composition fixed at 1.4% and N concentrations varying in the range [N] = 1.8 × 1018–5.1 × 1019 cm−3. Structural analysis by x-ray diffraction (XRD) detects some additional extrinsic diffraction peaks possibly from Fe-N compounds in the N-doped film with [N] = 5.1 × 1019 cm−3 only. Accordingly, x-ray absorption fine structure (XAFS) analysis reveals the shifting of Fe atoms from substitutional position for N-doped films with high N concentrations, [N] ≥ 1.8 × 1019 cm−3, whereas N-doped films with intermediate N concentrations [N] ≤ 4.3 × 1018 cm−3 are composed of pure diluted phase with substitutional Fe atoms in the valence state deviating from Fe2+. Magnetization measurement using SQUID confirms drastic change of magnetic properties; the linear dependence of magnetization on magnetic field, typical of van Vleck-type paramagnetism in the film without N-doping changes into room temperature ferromagnetic behaviors with hysteretic magnetization curves for N-doped films. The observed weak room temperature ferromagnetic behavior of the N-doped films with [N] ≤ 4.3 × 1018 cm−3 may reflect the deviation of substitutional Fe valence state from Fe2+ to Fe2+/3+ mixed states. On the other hand, the robust room temperature ferromagnetic behavior exhibited by N-doped films with [N] ≥ 1.8 × 1019 cm−3 may originate from precipitates of Fe-N compounds with Fe being in Fe2+/3+ or other valence state.