InCrP:Zn was prepared using the implantation with Cr concentrations of 0.3% and 0.7%, respectively. It was confirmed that the photoluminescence peaks near 0.85(D, Cr)eV and 0.96(e,Cr)eV were Cr-correlated PL bands by the implantation of Cr. Especially, each 0.85(D, Cr)eV and 0.96(e,Cr)eV peaks were separately observed based on InP. In triple-axis x-ray diffraction patterns, the samples revealed a shoulder peak indicative of intrinsic InCrP. Ferromagnetic hysteresis loops measured at 10K and 300K were observed and the temperature-dependent magnetization showed ferromagnetic behavior ≥300K, which reveals obvious and enhanced ferromagnetic spin coupling mediated by hole.

We fabricated high quality epitaxial Bi0.9Ho0.1FeO3 thin films which exhibited the tetragonally stained structure with a c/a ratio of about 1.04. The Bi0.9Ho0.1FeO3 thin film showed a good ferroelectric property with the high remanent polarization (P-r) of about 80 mu C/cm(2). The ferromagnetic hysteresis loop with a clear remanent magnetization was shown. The coercive field and the remanent magnetization of the Bi0.9Ho0.1FeO3 film are 6200 Oe and 1.7 emu/g, respectively. The abrupt conduction due to space charge limited (SCL) was revealed in leakage current density versus electric field. (C) 2012 Elsevier B.V. All rights reserved.

One layer of self-assembled Ge quantum dots with Si barrier were grown on high resistivity (100) p-type Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. A presence of ferromagnetic structure was confirmed in the dilute magnetic quantum dots (DMQD). The DMQD through 10 min annealing was found to be homogeneous, and to exhibit p-type conductivity, insulating property, and ferromagnetic ordering with a Curie temperature, T c =170 K. On the other hand, the DMQD through 30 and 60 min annealing was found to be semi-insulating and ferromagnetic ordering with a Curie temperature over 300 K. The XRD data show that there is a phase separation of Mn rich phases Mn 5 Ge 3 from MnGe nanostructure. Therefore, it is likely that the ferromagnetic exchange coupling of sample with T c =170 K is hole-mediated and the ferromagnetism in sample with T c >300 K is due to Mn 5 Ge 3 phase.

Multistacked Ge quantum dots (QDs) with Si spacers of different thicknesses have been grown on (100) Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. The presence of a ferromagnetic structure was confirmed in the insulating (Si0.45Ge0.55)Mn-0.03 diluted magnetic quantum dots (DMQD) and semiconducting (Si0.45Ge0.55)Mn-0.05 DMQD. The DMQD materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with Curie temperatures T-C = 350 and 160 K respectively. The x-ray diffraction (XRD) data show that there is a phase separation of Mn5Ge3 from the MnGe nanostructure. Temperature-dependent electrical resistivity in the semiconducting DMQD material indicates that manganese introduces two acceptor levels in germanium at 0.14 eV from the valence band and 0.41 eV from the conduction band implying that Mn substitutes for Ge. Therefore, it is likely that the ferromagnetic exchange coupling of DMQD material with T-C = 160 K is hole-mediated due to formation of bound magnetic polarons and the ferromagnetism in the sample with T-C >300 K is due to Mn5Ge3 phase.

Ferromagnetic Ga1−xMnxAs layers (where x=1.4–3.0%) grown on (100) GaAs substrates by molecular beam epitaxy were characterized using Raman spectroscopy. As Mn is introduced into GaAs, a marked increase in disorder in the material occurs, as indicated by the growth of the disorder-allowed transverse-optical Raman line. Another important result is that as the Mn concentration in Ga1−xMnxAs increases further beyond ca. 2%, Raman-active coupled-plasmon-longitudinal-optical phonon modes arise, which signals the increasing presence of holes, and thus provides a useful tool for determining their concentration. Using the depletion-layer approach from the Raman spectroscopy data, we determined the carrier concentration for samples with x=2.2% and 3.0% was to be 7.2×1019 and 8.3×1020cm−3, respectively.

We have investigated the temperature and composition dependent photoluminescence (PL) spectra in Ga1−xMnxN layers (where x≈0.1–0.8%) grown on sapphire (0001) substrates using the plasma-enhanced molecular beam epitaxy technique. The efficient PL is peaked in the red (1.86eV), yellow (2.34eV), and blue (3.29eV) spectral range. The band-gap energy of the Ga1−xMnxN layers decreased with increasing temperature and manganese composition. The band-gap energy of the Ga1−xMnxN layers was modeled by the Varshni equation and the parameters were determined to be α=2.3×10−4, 2.7×10−4, 3.4×10−4eV/K and β=210, 210, and 230K for the manganese composition x=0.1%, 0.2%, and 0.8%, respectively. As the Mn concentration in the Ga1−xMnxN layers increased, the temperature dependence of the band-gap energy was clearly reduced.

We have investigated the temperature-dependent photoluminescence (PL) spectra in Ga1−xMnxN layers (where x≈0.1–0.8%) grown on sapphire (0 0 0 1) substrates using the plasma-enhanced molecular beam epitaxy technique. All the layers doped with manganese exhibited n-type conductivity with Curie temperature over 350 K. The efficient PL are peaked in the red (1.86 eV), yellow (2.34 eV), and blue (3.29 eV) spectral range. It was found that the blue band at 3.29 eV is mostly associated with the formation complexes between donors (e.g., N vacancy) and Mn acceptors, which results in forming donor levels at 0.23 eV below the conduction band edge. The yellow band is attributed to intrinsic gallium defects. The broad band at 1.86 eV is attributed to inner 5D state transition (T2 to E) of Mn ions.

Ten and twenty layers of self-assembled Ge QDs with 44 and 59-nm-thick Si barrier were grown on high resistivity (100) p-type Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. A presence of ferromagnetic structure was confirmed in the insulating GeMn diluted magnetic quantum dots (DMQD) and semiconducting GeMn DMQD. The DMQD materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with a Curie temperature, TC=350 and 230K. The X-ray diffraction (XRD) data show that there is a phase separation of Mn5Ge3 from MnGe nanostructure. Temperature dependent electrical resistivity in semiconducting DMQD material indicates that manganese introduces two acceptor levels in germanium at 0.14eV from the valence band and 0.41eV from the conduction band implying Mn substituting Ge. Therefore, it is likely that the ferromagnetic exchange coupling of DMQD material with TC=230K is hole-mediated due to formation of polarons and the ferromagnetism in sample with TC>300K is due to Mn5Ge3 phase.

Capacitance-voltage (C-V) and Deep-level transient spectroscopy (DLTS) measurements on AlxGa1-xN/GaN heterostructures were performed to investigate the existence of the carriers and the behavior of the deep levels in the AlxGa1-xN/GaN heterointerface. The C-V depth profile showed that the carrier concentration existed at the AlxGa1-xN/GaN heterointerface was 4 × 1012 cm2. The DLTS results showed two deep levels. The capture cross-section of the deep level related to the two-dimensional electron gas decreased with increasing depth, resulting from the existence of the different deep levels in each region.

Si1−xMnx diluted magnetic semiconductors with x≈5% with a ferromagnetic structure were formed through Mn ion implantation and post-annealing. The temperature- and magnetic field-dependent magnetization were measured by magnetometry using a superconducting quantum interference device. The Si0.95Mn0.05 materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with a Curie temperature (TC) above room temperature. The low-temperature (T=10K) photoluminescence spectra exhibited Mn-related free-to-donor pair transitions for the Si1−xMnx materials with x≈5%. A Mn double-donor level in these samples was found to be Mn substituted for Si (MnSi) and located around 290meV above the valence band, suggesting that the ferromagnetism observed in Mn-implanted Si material is hole-mediated ferromagnetism.

Ferromagnetic Ga1−xMnxAs layers (where x≈4.7–5.5%) were grown on (100) GaAs substrates by molecular beam epitaxy. These p-type (Ga,Mn)As films were revealed to have a ferromagnetic structure and ferromagnetism is observed up to a Curie temperature of 318K, which is ascribed to the presence of MnAs secondary magnetic phases within the film. It is highly likely that the phase segregation occurs due to the high Mn cell temperature around 890–920°C, as it is well established that GaMnAs is unstable at such a high temperature. The MnAs precipitate in the samples with x≈4.7–5.5% has a Curie temperature Tc≈318K, which was characterized from field-cooled and zero-field-cooled magnetization curves.

Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.

Ga 1− x Mn x N layers (where x ≈ 10.4–12.5%) containing Mn 3 GaN precipitates were grown on (0 0 0 1) sapphire substrates using molecular beam epitaxy, and were shown to exhibit two ferromagnetic phases. These p-type GaMnN films were revealed to have a well defined hysteresis loop up to T ∼ 200 K, which originates from the appreciable number of Mn 3 GaN precipitates imbedded in the GaN matrix. The precipitated GaMnN samples exhibited a ferromagnetism due to Mn 3 Ga clusters mixed with Mn 3 GaN precipitates in the high temperature region (above 200 K). The Mn 3 GaN precipitates and Mn 3 Ga clusters were identified by X-ray diffraction and transmission electron microscopy. Mn 3 GaN precipitates in the samples with a high Mn concentration have a characteristic transition temperature at T ∼ 200 K, which was characterized from field-cooled and zero-field-cooled magnetization curves.

One layer of self-assembled Ge quantum dots with Si barrier were grown on high-resistivity p-type Si(100) substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and postannealing. A presence of ferromagnetic structure was confirmed in the diluted magnetic quantum dots (DMQDs). The DMQDs through 10 min annealing were found to be homogeneous and to exhibit p-type conductivity, semiconducting property, and ferromagnetic ordering with a Curie temperature, T-C = 170 K. The DMQDs through 60 min annealing were found to be semi-insulating and ferromagnetic ordering with a Curie temperature over 300 K. The X-ray diffraction data show that there is a phase separation of Mn-rich phases Mn5Ge3 from MnGe nanostructure. Temperature-dependent electrical resistivity data indicates that manganese introduces two acceptor levels in germanium at 0.14 or 0.13 eV from the valence band and 0.46 or 0.43 eV from the conduction band, implying that Mn is substituting Ge. Therefore, it is likely that the ferromagnetic exchange coupling of the sample with TC = 170 K is hole-mediated and the ferromagnetism of the sample with T-C > 300 K is due to Mn5Ge3 phase. (c) 2007 The Electrochemical Society.

The magnetotransport properties of ferromagnetic Ga1−xMnxAs epilayers with Mn mole fractions in the range of x≈2.2%–4.4% were investigated using Hall effect measurements. The temperature-dependent Hall carrier concentration for a metallic sample with x≈2.2% was analyzed assuming an activation energy from two acceptor levels. It was found that the two acceptor levels with activation energies of 129.4 and 31.6 meV at B=0Oe decreased to 87.6 and 30.7 meV, respectively, at B=5kOe. The decrease in acceptor activation energy from 129.6 to 87.6 meV was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for the increase in carrier concentration. From magnetic-field-dependent Hall resistance data, the Curie temperature was estimated to be TC=60 and 70 K for Ga1−xMnxAs samples with x≈2.2 and x≈4.4%, respectively. The magnetoresistance measurements confirmed that the anomalous Hall effect existed in these samples that showed metallic and insulating behavior, respectively.

Gallium nitride heterostructures sandwiched between AlGaN layers have been grown on sapphire substrates using rf-plasma-assisted molecular-beam epitaxy (MBE), and their electrical properties investigated. Deep-level transient spectroscopy (DLTS) measurements reveal that the activation energies of the two electron levels were 0.21 eV and 0.23 eV relative to the conduction band, with capture cross sections of 5.0×10-15 cm2 and 7.4×10-17 cm2, respectively. From the capture kinetics of the deep-level defects, according to the filling pulse duration and the bias voltage, it is suggested that the 0.21 eV defect is associated with nitrogen vacancies and the 0.23 eV defect is associated with extended defects.

The magneto-transport properties of ferromagnetic Ga1−xMnxAs epilayers with Mn mole fractions in the range of x≈2.2–4.4% were investigated through Hall effect measurements. The magnetic field-dependent Hall mobility for a metallic sample with x≈2.2% in the temperature range of T=0–300K was analyzed by magnetic field-dependent mobility model including an activation energy of Mn acceptor level. This model provides outstanding fits to the measured data up to T=300K. It was found that the acceptor levels with activation energies of 112meV at B=0Oe decreased to 99meV at B=5kOe in the ferromagnetic region. The decrease in acceptor activation energy was due to the spin splitting of the Mn acceptor level in the ferromagnetic region, and was responsible for increase in carrier concentration.