The Fermi level dependence of the optical and magnetic properties ofGa1−xMnxN grown by metal–organic chemical vapour deposition

Abstract

The suppression of the ferromagnetic behaviour of metal–organic chemical vapour deposition grownGa1−xMnxN epilayers by silicon co-doping, and the influence of the Fermi levelposition on and its correlation with the magnetic and optical properties ofGa1−xMnxN are reported. Variation in the position of the Fermi level in the GaN bandgapis achieved by using different Mn concentrations and processing conditions aswell as by co-doping with silicon to control the background donor concentration.The effect on Mn incorporation on the formation of defect states and impurityinduced energy states within the bandgap of GaN was monitored by means ofphotoluminescence absorption and emission spectroscopy. A broad absorption detectedaround 1.5 eV is attributed to the presence of a subband introduced by Mn inducedenergy states due to temperature independent transition energies and linewidths.The intensity and the linewidth of the absorption band correlate with the Mnconcentration. Similarly, the magnitude of the magnetization decreases as the Fermilevel approaches the conduction band, as the Fermi energy is increased above theMn (0/−) acceptor state.Silicon concentrations>1019 cm−3 caused the complete loss of ferromagnetic behaviour in the epilayer. The absorption bandat 1.5 eV is also not observed upon silicon co-doping. The observed spectroscopic datafavour a double-exchange-like mechanism rather than an itinerant free carrier mechanismfor causing the ferromagnetism. This behaviour significantly differs from the propertiesreported for widely studied (Ga, In)MnAs.