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The magnetization of p-GaN or p-AlGaN/GaN superlattices was measured after implantation with high doses (3–5×1016 cm−2) of Mn, Fe, or Ni and subsequent annealing at 700–1000 °C. The samples showed ferromagnetic contributions below temperatures ranging from 190–250 K for Mn to 45–185 K for Ni and 80–250 K for Fe. The use of superlattices to enhance the hole concentration did not produce any change in ferromagnetic ordering temperature. No secondary phase formation was observed by x-ray diffraction, transmission electron microscopy, or selected area diffraction pattern analysis for the doses we employed.

High concentrations of Cr (3–5at.%) were incorporated into GaN during molecular beam epitaxy. There was no evidence of significant formation of deep midgap states due to substitutional Cr acceptors. The results of optical absorption measurements and microcathodoluminescence measurements point to formation of a proper solid solution with the band gap lower than undoped GaN. GaCrN shows n-type conductivity. Increasing the Cr concentration increases the electrical resistivity, leads to a stronger optical absorption in the above-band-gap region, enhances the intensity of the yellow band near 2.3eV, and promotes the formation of electron traps with the activation energy of 0.2eV.

The spin injection dynamics of GaMnN∕InGaN multiquantum well (MQW) light emitting diodes (LEDs) grown by molecular beam epitaxy were examined using picosecond-transient and circularly polarized photoluminescence (PL) measurements. Even with the presence of a room temperature ferromagnetic GaMnN spin injector, the LEDs are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN MQW, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection. Typical photoluminescence decay times were 20–40ns in both commercial GaN MQW LEDs with emission wavelengths between 420–470nm and in the GaMnN∕InGaN multi-quantum well MQW LEDs. In the wurtzite InGaN∕GaN system, biaxial strain at the interfaces give rise to large piezoelectric fields directed along the growth axis. This built-in piezofield breaks the reflection symmet...

Doping of AlN with Cr at percent level concentrations produces ferromagnetism persisting to above 300K. We have examined the electrical and optical properties of Cr-doped AlN grown by molecular beam epitaxy under conditions that produce single-phase or multiple phase material, as measured by x-ray diffraction. The band gap of single-phase AlN decreases from 6.2 to 6.1eV for a Cr concentration of 2at.%. This change originates from the Franz-Keldysh broadening of the band edge due to potential fluctuations caused by heavy Cr doping. The effect was more pronounced in multiple-phase samples (the secondary phases are Cr2N and AlxCry), producing an apparent band gap of 5.8eV. Two strong defect absorption bands with thresholds of 3 and 5eV are introduced by the Cr doping. The resistivity of single-phase AlCrN samples is higher than the resistivity of similarly grown undoped AlN films. Multiple-phase AlCrN samples show a high conductivity of the hopping type. The optical transmission spectra of multiphase AlCrN i...

Ion implantation of Mn at concentrations of 1–5 at. % was performed in AlxGa1−xP:C (x=0, 0.24, 0.38, and 0.54) epilayers grown by gas source molecular beam epitaxy. Ferromagnetic-like ordering at 300 K was observed for Mn doses up to 3 at. % for all Al subfractions in superconducting quantum interference device measurements. The calculated magnetic moment was found to peak at 3 at. % Mn in plots of magnetization versus Mn for all four Al subfractions. For a given Mn concentration, the magnetic moment was found to initially increase then decrease in plots of magnetization versus Al subfraction. Structural characterization revealed the presence of the Mn2P and Mn3Ga phases in Al0.54Ga0.46P:C layers implanted with 5 at. % Mn, while no second phases were observed in any other combinations of Al and Mn. A substantial increase in magnetic ordering temperature predicted by theory for AlxGa1−xP:C films compared to GaP:C films with Mn incorporation was not observed.

The magnetization of the dilute magnetic alloy GaMnP:C prepared by the implantation of Mn into p-GaP:C or by direct molecular-beam epitaxy is reported. The material implanted to produce a Mn level of 3% produces ferromagnetic behavior that persists up to a temperature of 330 K, while the epitaxially derived material shows evidence of ferromagnetism at a temperature of 300 K. In both cases, no second phases were observed by x-ray diffraction, transmission electron microscopy, or selected area diffraction pattern analysis. A phase diagram of the GaMnP:C system, determined by epitaxial growth, is also reported.