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We calculate the formation enthalpies of PdHx (x = 0–3) by cluster expansion (CE) and calculations based on density functional theory. CE predicts the stable palladium hydride structures PdH, PdH2.67, and PdH2.75. The band structures and density of states indicate that the amount of hydrogen in the palladium lattice does not alter the metallic character of the palladium significantly. However, all PdHx structures with x > 1 have greater formation enthalpies than that of the given reaction path 4 PdH 2 = 2 PdH + 2 Pd + 3 H 2 and thus they are thermodynamically unstable. The shorter bond length of Pd–H and the smaller bond angle of Pd–H–Pd imply a higher cohesive energy in zincblende (ZB) PdH than that in rocksalt (RS) PdH. Bader charge analysis shows a stronger electronegativity of H atoms in ZB-PdH than that in RS-PdH. This results in a stronger Pd–H bond in ZB-PdH than that in RS-PdH. Thus ZB-PdH has lower formation enthalpy than that of RS-PdH. However, regarding the dynamic stability, we conclude that hydrogen atoms prefer to occupy the octahedral sites of the palladium lattice because of the lower zero-point energy and vibration free energy than that of occupying the tetrahedral sites.

In this paper we report the results on the study of the low-temperature photoluminescence of WO3 nanoparticles uncoated and coated by carbon. The photoluminescence spectra of WO3 nanoparticles at T = 15 K demonstrate the two sharp emission bands at 369 nm and 374 nm, respectively. The energy position, the small full width at half maximum (FWHM) of these bands and the strong quenching of the intensity with increasing temperature allowed us to attribute these emission bands to the radiative recombination of bound excitons. These excitons are localized on the donor states in the conduction band of WO3. The difference in the relative intensities of the bound exciton emission bands in the uncoated and the carbon coated WO3 nanoparticles is explained by the charge (electrons) transfer from the WO3 nanoparticles to the carbon coating layer.

The realization and application of optoelectronics, photonics, and sensing, such as in solar diode sensors and photodiodes, which are potentially useful from ultraviolet to infrared light sensing, is dramatically advanced when ZnO is integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Here, we compare and analyze the fundamental features of the Si-ZnO coaxial nanorod heterostructures (Si@ZnO NRs) grown on semi-insulating (100)-oriented Si substrates at growing temperatures of 500°C, 600°C, 650°C, and 700°C of the Si layer for device applications. ZnO NRs were grown by a vapor phase transport, and Si layers were made by rapid thermal chemical vapor deposition. X-ray diffraction, field emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy, and Raman experiments showed that ZnO NRs were single crystals with a wurtzite structure, while the Si layer was polysilicon with a zincblende structure. Furthermore, FESEM revealed that Si shell thickness of the Si@ZnO NRs increases with increasing growing temperatures of Si from 500°C to 700°C.

Above room temperature, ferromagnetic behavior is achieved in Si through Fe ion implantation. The incorporation of Fe in Si was confirmed by an X-ray diffraction and a superconducting quantum interference device. Fe-implanted Si magnetic semiconductors annealed at 800 and 900 ∘C for 25 min were found to have a ferromagnetic ordering with a Curie temperature above room temperature. X-ray diffraction (XRD) measurements strongly revealed that iron silicide were formed, suggesting that the ferromagnetism observed in Fe-implanted Si magnetic semiconductor is due to phase segregation into iron silicide. Even at low implantation dose, we observed the formation of Fe silicide phase responsible for the high temperature magnetic behavior. These measurements strongly support the formation of Fe silicide phase and provide strong evidence of the existence of the Fe silicide phase that determines Curie temperature.

The thermodynamic behavior of excitonic emission properties in manganese- and zinc-codoped indium phosphide (InMnP:Zn) diluted magnetic semiconductor (DMS) layers was investigated. Compared to the InMnP:Zn DMS layer (Mn ≈ 0.06%), the inhomogeneous thermal-broadening of the excitonic-emission line-width in InMnP:Zn DMS layer (Mn ≈ 0.29%) is dominant at lower temperatures. This is attributed to the increase of ionized impurity scattering from Mn ions and results in the increase of exciton–phonon coupling strength. As a consequence, high Mn content can lead to low excitonic emission efficiency, although generally a larger Mn content is favorable to increase the Curie temperature of a DMS material.

The p-type InMnP:Be epilayers, which were prepared by thermal diffusion of Mn through in-situ deposition of Mn layer using molecular beam epitaxy (MBE) onto MBE-grown InP:Be epilayers and subsequent in-situ annealing at 300–350 °C, were investigated. InMnP:Be epilayers prepared by the above sequence clearly showed the Mn-related emission band at 1.1–1.2 eV, which indicates the effective incorporation of Mn 2+ ions into the host layer InP:Be. The samples demonstrated very large ferromagnetic hysteresis loops with enhanced coercivity, and the ferromagnetic-to-paramagnetic transition of the samples was observed to occur at ∼85 K. These results suggest that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be effectively formed by the above-mentioned sequential in-situ processes.

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)Mn0.03 diluted magnetic quantum dots (DMQD) and semiconducting (Si0.45Ge0.55)Mn0.05 DMQD. The DMQD materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with Curie temperatures TC = 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 TC = 160 K is hole-mediated due to formation of bound magnetic polarons and the ferromagnetism in the sample with TC > 300 K is due to Mn5Ge3 phase.

We have investigated the temperature and composition dependent photoluminescence (PL) spectra in Ga 1− x Mn x N layers (where x ≈ 0.1–0.8%) grown on sapphire (0 0 0 1) substrates using the plasma-enhanced molecular beam epitaxy technique. The efficient PL is peaked in the red (1.86 eV), yellow (2.34 eV), and blue (3.29 eV) spectral range. The band-gap energy of the Ga 1− x Mn x N layers decreased with increasing temperature and manganese composition. The band-gap energy of the Ga 1− x Mn x N 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 −4 eV/K and β = 210, 210, and 230 K for the manganese composition x = 0.1%, 0.2%, and 0.8%, respectively. As the Mn concentration in the Ga 1− x Mn x N layers increased, the temperature dependence of the band-gap energy was clearly reduced.

Ten and twenty layers of self-assembled Ge QDs with 44 and 59-nm-thick Si barrier were grown on high resistivity (1 0 0) 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, T C = 350 and 230 K. The X-ray diffraction (XRD) data show that there is a phase separation of Mn 5 Ge 3 from MnGe nanostructure. Temperature dependent electrical resistivity in 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 Mn substituting Ge. Therefore, it is likely that the ferromagnetic exchange coupling of DMQD material with T C = 230 K is hole-mediated due to formation of polarons and the ferromagnetism in sample with T C > 300 K is due to Mn 5 Ge 3 phase.

Si 1− x Mn x 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 Si 0.95 Mn 0.05 materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with a Curie temperature ( T C ) above room temperature. The low-temperature ( T = 10 K ) photoluminescence spectra exhibited Mn-related free-to-donor pair transitions for the Si 1− x Mn x materials with x ≈5%. A Mn double-donor level in these samples was found to be Mn substituted for Si (Mn Si ) and located around 290 meV above the valence band, suggesting that the ferromagnetism observed in Mn-implanted Si material is hole-mediated ferromagnetism.

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=0–300 K 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=300 K. It was found that the acceptor levels with activation energies of 112 meV at B=0 Oe decreased to 99 meV at B=5 kOe 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.

Ferromagnetic Ga1−xMnxAs epilayers with Mn mole fraction in the range of x≈2.2–4.4% were grown on semi-insulating (100) GaAs substrates using the molecular beam epitaxy technique. The transport properties of these epilayers were investigated through Hall effect measurements. The measured hole concentration of Ga1−xMnxAs layers varied from 4.4×1019 to 3.4×1019 cm−3 in the range of x≈2.2–4.4% at room temperature. From temperature dependent resisitivity data, the sample with x≈4.4% shows typical behavior for insulator Ga1−xMnxAs and the samples with x≈2.2 and 3.7% show typical behavior for metallic Ga1−xMnxAs. The Hall coefficient for the samples with x≈2.2 and 4.4% was fitted assuming a magnetic susceptibility given by Curie–Weiss law in a paramagnetic region. This model provides good fits to the measured data up to T=300 K and the Curie temperature Tc was estimated to be 65, 83 K and hole concentration p was estimated to be 5.1×1019, 4.6×1019 cm−3 for the samples with x≈2.2 and 4.4%, respectively, confirming the existence of an anomalous Hall effect for metallic and insulating samples.

Mn-doped Ga1−xMnxAs epilayers grown on semi-insulating (100) GaAs substrates using the liquid phase epitaxy technique were investigated using photoluminescence and Hall effect measurements from 20 to 300 K. Transitions involving shallow Mn acceptors were identified through photoluminescence measurements and the ionization energy of Mn acceptor was determined to be 104.6 meV which is in good agreement with values calculated from a hydrogenic hole model including sp–d exchange contribution. Also, it was concluded that Ga1−xMnxAs alloys were obtained from samples with low Mn concentration (below x≈1%) and these layers have a simple impurity band merging to the valence band.

Dominant hole traps of ferromagnetic Ga1−xMnxAs and epilayers with an Mn mole fraction of x≈2.2% and 4.4% were identified employing deep-level transient spectroscopy. Three hole traps with binding energies of EA=0.38±0.01 eV at 140 K, EB=0.43±0.01 eV at 220 K, and EC=0.65±0.01 eV at 300 K above the top of the valence band were observed. Comparing with theoretical data of GaAs, it appears most likely that the trap with EA is associated with a gallium vacancy (VGa) or the arsenic antisite complex (GaAs+VAs), whereas the traps with EB and EC are associated with two charge states of arsenic antisite (AsGa) defect. The hole capture cross sections were determined as σp(A)=3.7×10−11, σp(B)=1.5×10−14, and σp(C)=1.1×10−14 cm2, respectively. The samples with x≈2.2% and x≈4.4% show typical behavior for metallic Ga1−xMnxAs and insulator Ga1−xMnxAs, respectively, through Hall measurements.

The deep trap levels of AlxGa1−xN films with x in the range from 0 to 0.15 grown on c-plane sapphire substrates using rf-plasma-assisted molecular-beam epitaxy have been investigated by deep level transient spectroscopy measurements. Two distinct defect levels (denoted as Ei and Di) were observed. The origins of the Ei and the Di are associated with point defects such as the N vacancies and extended defects, such as the threading dislocations, respectively. According to Al content (x), the activation energy and capture cross section for the Di defect ranged from 0.19to0.41eV and 1.1–6.6×10−15cm2, respectively. The trap energy levels of Di defects in AlxGa1−xN were calculated and the values were nonlinear with Al content. The bowing parameter of AlxGa1−xN films was determined to be b=1.22.

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.