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The influence of growth temperature on the surface morphology and luminescence properties of Eu-doped GaN layers grown by organometallic vapor phase epitaxy was investigated. By using a Eu source that does not contain oxygen in its molecular structure, and varying the growth temperature, the local defect environment around the Eu3+ ions was manipulated, yielding a higher emission intensity from the Eu3+ ions and a smoother sample surface. The optimal growth temperature was determined to be 960 °C and was used to fabricate a GaN-based red light-emitting diode with a significantly higher output power.

Ag electrodes were formed on InGaN/GaN multi-quantum well blue light emitting diode (LED) substrates by using needle-type dispensing of Ag nanoink and the heat treatment as wet processes. The patterns by using the needle-type dispenser system are drawn out of a dot matrix method like an inkjet printer, and thus, arbitrary graphics can be produced. After patterning, the conductive Ag films as electrodes were formed by sintering at 450°C for 30 minutes under the atmospheric conditions. The fabricated LED emitted blue light with a threshold and operating voltage of 3.3 and 4.4 V, respectively. These results suggest that the wet processed Ag electrodes have a potential for use in the production of GaN based LEDs.

The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.

The in situ Eu doping into GaN grown with various conditions by organometallic vapor-phase epitaxy is reviewed along with the luminescence properties, magneto-optical behavior, and application to p-n junction-based light-emitting diodes with a low-voltage current injection. By optimizing the growth conditions and device structures, the light output power has increased up to sub-mW at an injected current of 20 mA. For further improvement of the emission efficiency for the development of the output power, preferential formation of efficient Eu luminescent centers is strongly desired. A model for the efficient Eu luminescent sites is discussed in relation to the local structures around Eu ions that include intrinsic and/or extrinsic defects.

We investigate resonantly excited photoluminescence from a Eu,O-codoped GaN layer embedded into a microcavity, consisting of an AlGaN/GaN distributed Bragg reflector and a Ag reflecting mirror. The microcavity is responsible for a 18.6-fold increase of the Eu emission intensity at ∼10K, and a 21-fold increase at room temperature. We systematically investigate the origin of this enhancement, and we conclude that it is due to the combination of several effects including, the lifetime shortening of the Eu emission, the strain-induced piezoelectric effect, and the increased extraction and excitation field efficiencies. This study paves the way for an alternative method to enhance the photoluminescence intensity in rare-earth doped semiconductor structures.

The dependence of Eu3+ photoluminescence (PL) properties on Eu concentration was studied in Eu-doped ZnO (ZnO:Eu) thin films grown by sputtering-assisted metalorganic chemical vapor deposition (SA-MOCVD). The ZnO:Eu showed band-edge PL from ZnO and red emission lines due to the intra-4f transitions in Eu3+ ions at room temperature (RT). The intensities of band-edge and Eu3+ PL decreased with the increasing Eu concentration. In the temperature dependence of Eu3+ PL, the ZnO:Eu with high Eu concentration showed large thermal quenching of the PL intensity. In addition, the lifetimes of Eu3+ PL became short at high Eu concentration. The concentration quenching mechanism of Eu3+ PL using a model based on non-radiative recombination processes in ZnO and Eu3+ ions was presented.

Direct bandgap energy (Eg) and lattice deformations were investigated in β-FeSi2 epitaxial films grown by molecular beam epitaxy (MBE) with different growth condition. As Si/Fe flux ratio during the MBE growth became smaller than Si/Fe = 2.0, the lattice constants deviated from those of β-FeSi2 single crystal, which indicated an enhanced lattice deformation at the lower Si/Fe ratio. In photoreflectance (PR) measurements, the PR spectra shifted to lower photon energy with the enhanced lattice deformation. These results revealed that the Eg of β-FeSi2 epitaxial film was modified by the lattice deformation depending on the growth condition.

We perform photoluminescence measurement of GaAs:Er,O under a pulsed magnetic field up to 60 T and succeed to obtain the magnetic field dependence of three main photoluminescence peaks. We also estimate the energy splitting of states 4I15/2 and 4I13/2 using the crystal field theory. Theoretically calculated energy differences between the lowest state of J= 13 2 and the lowest three states of J= 15 2 are in good agreement with experimentally obtained energy of three main PL peaks. We discuss the local configuration around the luminescent Er-2O center. By using parameters in the crystal field calculation, our analysis suggest that not only O2− sites but also As3− sites adjacent to Er3+ ion are displaced from their original lattice positions.

The modifications of direct transition energies by lattice deformations were investigated in β-FeSi 2 epitaxial films, polycrystal films and single crystal, systematically. The lattice deformations depending on thermal annealing temperature ( T a ) were observed in β-FeSi 2 epitaxial films. In photoreflectance (PR) measurements, the direct transition energies of the epitaxial films shifted to lower energies as the T a increased. The polycrystal films did not show the lattice deformation and the shift of direct transition energies. These results show that the direct bandgap is modified by the lattice deformation originating from the lattice mismatch at the hetero-interface of β-FeSi 2 /Si.

The incorporation of Eu ions into GaN has been studied using combined excitation–emission spectroscopy for samples that were in situ doped during organometallic vapor-phase epitaxy (OMVPE) growth. The obtained fingerprints of characteristic emission spectra are subsequently used to determine the coupling of the Eu ions to the crystal lattice. We find a majority site, which exhibits coupling to bulk-like phonon modes as well as a localized phonon mode. For this site, we also find that the zero-phonon line of the 7F0 to 5D0 transition, which is forbidden, is much weaker than the phonon-coupled excitation transitions. The ratio of zero-phonon to phonon-coupled transition strength depends on the crystalline quality of the layer. These observations are consistent with the assignment of the majority site to an unperturbed Eu ion on Ga position. We find that the relative abundance of the majority site is strongly underestimated whenever the zero-phonon 7F0 to 5D0 excitation transition is used as a measure.

We obtained room-temperature red emission from GaN-based light-emitting diodes (LEDs) using a Eu-doped GaN (GaN:Eu) as an active layer. The bright emission was observed under normal lighting condition, which is associated with the intra-4f shell transition of Eu 3+ ions. The LED properties depends on the growth condition of GaN:Eu layer. Since the high-quality GaN can be grown at higher growth pressure, the intense electroluminescence (EL) was observed in the LED with a GaN:Eu active layer grown at atmospheric pressure, which is due to the enhancement of the energy transfer efficiency from the GaN host material to the Eu ions. At a d.c. current of 20 mA, the light output power and external quantum efficiency were 17 μW and 0.04%, respectively. These results indicate the feasibility of GaN:Eu to realize a GaN-based red emitter for fabrication of nitride-based monolithic optical devices.

This paper presents the device-level electrostatic discharge (ESD) robustness improvement for integrated vertical double-diffused MOS (VDMOS) and lateral double-diffused MOS (LDMOS) transistors by changing device structure. The ESD robustness of VDMOS transistor was improved by preventing current concentration and that of LDMOS transistor was improved by relaxing the electric field under the LOCOS oxide. We found the different gate-voltage dependence of the second breakdown current (It2) between VDMOS and LDMOS transistors. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Temperature dependence of direct transition energies ( E g ) was investigated in β - FeSi 2 epitaxial films on Si(111) substrate. The lattice volume of the epitaxial films was reduced as the annealing temperature ( T a ) increased. In photoreflectance measurements, the samples annealed at higher T a showed a larger temperature dependence of E g . These results revealed that the temperature dependence of E g depended on the lattice deformation by the thermal annealing. The fact supports the band gap modifications by the lattice deformation.

Photoluminescence (PL) and photoreflectance (PR) properties were investigated in Si/ β - FeSi 2 /Si(001) double heterostructure (DH) samples. The as-grown sample did not show clear PL, but the annealed one showed the 1.54 μ m PL. In PR spectra, the direct transition energies ( E g ) were observed at 0.910–0.935 eV in the samples. The E g shifted to lower photon energy with the increase of annealing temperature, which indicates a modification of the band structure. These results revealed that the 1.54 μ m PL was related to the transition at the indirect band gap. The effect of thermal annealing on the 1.54 μ m PL was discussed.

We investigated the luminescence properties of the Eu-doped GaN (GaN:Eu) grown at atmospheric (100 kPa) and low (10 kPa) pressures by organometallic vapor phase epitaxy (OMVPE). Although Eu concentration of atmospheric pressure GaN:Eu (AP-GaN:Eu) is lower than that of low pressure GaN:Eu (LP-GaN:Eu), the integrated photoluminescence (PL) intensity of the AP-GaN:Eu was 10 times higher than that of the LP-GaN:Eu (A. Nishikawa et al., Appl. Phys. Lett. 97, 051113 (2010)). Temperature dependent PL and time-resolved PL measurements revealed that the improved PL intensity was attributed to the higher crystal quality of the AP-GaN:Eu compared to that of the LP-GaN:Eu, which resulted in the enhancement of the energy transfer efficiency from the GaN host material to the Eu ions and in the increase in the number of optically active Eu ions.

Past research has shown that indirect excitation of Er3+ ions in SiO2 solid-state matrix with Si nanocrystals can be achieved by different pathways. Here, we investigate the impact excitation mechanisms in detail by means of time-resolved photoluminescence spectroscopy. We explicitly demonstrate that the free carrier impact excitation mechanism is activated as soon as the carriers obtain sufficient excess energy. The “hot” carriers with the above-threshold energy can be created upon optical pumping in two ways: either upon absorption of (i) a single photon with an energy exceeding a certain threshold hν > Eth or (ii) following absorption of multiple photons of lower energy in a single nanocrystal, hν Eth or (ii) following absorption of multiple photons of lower energy in a single nanocrystal, hν

A connection between condensed matter physics and basic quantum mechanics is demonstrated as we use the fundamental 3D particle-in-a-box model to explain the optical properties of semiconductor nanocrystals, which are substantially modified due to quantum confinement. We also discuss recent advances in the imaging and measurement capabilities of transmission electron microscopy, which have made it possible to directly image single nanocrystals while simultaneously measuring their characteristic absorption energies. We introduce the basic theory of nanocrystals and derive a simplified expression to approximate the optical bandgap energy of an orthorhombic nanocrystal. CsPbBr3 perovskite nanocrystals are used to demonstrate this model due to their cubic crystal structure, large absorption cross-section, and favourable dielectric properties, which make them ideal for exploring the applications of this simple classroom problem. Various orthorhombic shapes are explored, and the predicted values of the optical bandgap energies using the proposed model are shown to be in good agreement with the experimentally determined values.

CuPt-ordering and phase separation were directly investigated in In1-xGaxAsyP1-y with a low arsenic content grown by organometallic vapor phase epitaxy on GaAs substrates. CuPt-ordering and phase separation in samples grown at the substrate temperatures of 630 and 690 °C were characterized by transmission electron diffraction and transmission electron microscopy. Although the immiscibility of InGaAsP was enhanced at the lower substrate temperature, the sample grown at 630 °C showed less phase separation than the 690 °C-grown sample. The degree of CuPt-ordering was significantly enhanced in the sample grown at 630 °C. The results demonstrated that the CuPt-ordering originating from surface reconstruction of P(2×4) suppressed the phase separation even in the miscibility gap. The detailed characterization of the phase separation clearly revealed a vertical composition modulation (VCM) in InGaAsP for the first time. The mechanism of the VCM formation is discussed based on the modulated-strain field on the surface.

While InGaN/GaN blue and green light-emitting diodes (LEDs) are commercially available, the search for an efficient red LED based on GaN is ongoing. The realization of this LED is crucial for the monolithic integration of the three primary colors and the development of nitride-based full-color high-resolution displays. In this perspective, we will address the challenges of attaining red luminescence from GaN under current injection and the methods that have been developed to circumvent them. While several approaches will be mentioned, a large emphasis will be placed on the recent developments of doping GaN with Eu3+ to achieve an efficient red GaN-based LED. Finally, we will provide an outlook to the future of this material as a candidate for small scale displays such as mobile device screens or micro-LED displays.

In order to investigate the excitation processes in Eu,O-codoped GaN (GaN:Eu,O), the time-resolved photoluminescence signal including the rising part is analyzed. A rate equation is developed based upon a model for the excitation processes in GaN:Eu to fit the experimental data. The non-radiative recombination rate of the trap state in the GaN host, the energy transfer rate between the Eu3+ ions and the GaN host, the radiative transition probability of Eu3+ ion, as well as the ratio of the number of luminescent sites (OMVPE 4α and OMVPE 4β), are simultaneously determined. It is revealed and quantified that radiative transition probability of the Eu ion is the bottleneck for the enhancement of light output from GaN:Eu. We also evaluate the effect of the growth conditions on the luminescent efficiency of GaN:Eu quantitatively, and find the correlation between emission intensity of GaN:Eu and the fitting parameters introduced in our model.

While InGaN/GaN blue and green light-emitting diodes (LEDs) are commercially available, the search for an efficient red LED based on GaN is ongoing. This is essential for the monolithic integration of the three primary colors and the development of nitride-based small-size, full-color, high-resolution displays. We have succeeded in the realization of a red LED using Eu-doped GaN (GaN:Eu) grown by organometallic vapor phase epitaxy [1]. Making use of the intra-4f shell transitions of Eu3+ ions, our LED features an ultra-narrow linewidth of less than 1 nm at room temperature, and unprecedented thermal stability of 1 pm/K. By gradual optimization of the Eu excitation mechanism, we have increased the light output power above 1 mW at 20 mA [2]. One of limiting factors for enhanced light output power is the relatively long radiative lifetime of the Eu emission in GaN:Eu (∼300 µs). According to the Fermi’s golden rule, modifying the spontaneous emission rate of Eu ions can be achieved by increasing the photonic density of states (PDOS) at the frequency of spontaneous emission, as already demonstrated with a planar Fabry-Perot cavity. We have boosted the output power by actively manipulating radiative recombination probability at the atomic level of the Eu ions, which can be achieved through control of their photon fields in micro- and nano-cavities. In a GaN:Eu layer embedded in a microcavity consisting of an AlGaN/GaN distributed Bragg reflector (DBR) and a Ag reflecting mirror, a 21-fold increase of the Eu emission intensity was obtained under optical pumping at room temperature [3]. Furthermore, in a preliminary LED with a microcavity consisting of ZrO2/SiO2 and AlInN/GaN DBRs, the output power was enhanced by 5 times [4]. In this talk, current status of the red LED and strategies for further enhancement of the light output power are reviewed. A. Nishikawa, T. Kawasaki, N. Furukawa, Y. Terai, Y. Fujiwara, Appl. Phys. Exp. 2, 071004 (2009). B. Mitchell, V. Dierolf, T. Gregorkiewicz, and Y. Fujiwara, submitted to J. Appl. Phys. T. Inaba, D. Lee, R. Wakamatsu, T. Kojima, B. Mitchell, A. Capretti, T. Gregorkiewicz, A. Koizumi, Y. Fujiwara, AIP Adv. 6, 045105 (2016). T. Inaba, K. Shiomi, J. Tatebayashi, and Y. Fujiwara, in preparation.

We report on the epitaxial growth and the optical properties of Tm,Yb-codoped ZnO (ZnO:Tm,Yb) thin films by sputtering-assisted metalorganic chemical vapor deposition. The characteristic light emission due to the intra-4f shell transitions of Tm3+ and Yb3+ ions in the ZnO host is observed at 4 K by using photoluminescence (PL) characterization. The time-resolved PL measurements on the Tm3+ and Yb3+ emission reveals that the carrier decay time of each ion can vary by changing the concentration of both Tm3+ and Yb3+ ions, which depends on a mixing ratio of Tm2O3 and Yb2O3 in a sputtering target. The energy transfer from Tm3+ to Yb3+ ions occurs in the sample with the high mixing ratio, and the reversed energy transfer process occurs with the lower mixing ratio. These results indicate that the concentration, and thus the carrier dynamics of Tm3+ and Yb3+ ions in the ZnO:Tm,Yb host, can be controlled by altering the mixing ratio of the sputter target and the frequency power.

We have performed photoluminescence (PL) measurements on magnetic semiconductor GaAs:Er,O under pulsed magnetic fields up to 60 T at 4.2 K. We have succeeded in observing the Zeeman effect of the 4 I 13/2→4 I 15/2 PL transition of the Er3+ in the high magnetic field region. The effective g-factor of the dominant PL transition is estimated to be g eff=1.54±0.04. This value is in reasonable agreement with the theoretical value based on the crystal field theory.

Photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) grown by a sputtering-assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements at 300K, the samples annealed at 600°C for 30min showed clear red-emission lines due to the intra-4f shell transition of 5D0→7FJ (J = 2, 3) in Eu3+. In photoluminescence excitation (PLE) spectra, the PL were observed under the high-energy excitation above the band-gap energy of ZnO (indirect excitation) and the low-energy excitation resonant to the energy levels of 7F0-5D3 and 7F0-5D2 transitions in Eu3+ (direct excitation). These results revealed that the energy transfer from ZnO host to Eu3+ was accompanied under indirect excitation in ZnO:Eu.

We investigated the growth temperature dependence of luminescence properties in Eu-doped GaN layers grown by organometallic vapor phase epitaxy (OMVPE). The dominant photoluminescence (PL) peak intensity at 621 nm, due to the intra-4f shell transitions of 5D0-7F2 in Eu3+ ions, became the highest when the sample was grown at 1000°C. Above 1000°C, the PL peak intensity decreased because of the lower Eu concentration associated with the surface desorption of Eu ions. On the other hand, although the Eu concentration of the layer grown at 900°C was only half of the layer grown at 1000°C, the pronounced decline in the PL peak intensity was observed with decreasing growth temperature from 1000°C to 900°C, which results from the modification of the local structure around Eu ions. These results indicate that the growth temperature strongly influences the Eu concentration and the local structure around Eu ions. Therefore, an optimized growth temperature exists for strong Eu-related luminescence from Eu-doped GaN layer grown by OMVPE.

Low-temperature Er-related electroluminescence (EL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) light-emitting diode (LED) grown by organometallic vapor phase epitaxy. Under forward bias at 77 K, the EL spectra from a cleaved edge of the LED were dominated by the luminescence due to an Er–2O center, indicating that injected carriers contribute effectively to the excitation of the Er–2O center. Excitation cross-sections of Er ions by current injection were obtained by the current density dependence of the EL intensity and its time response. The excitation cross-sections depended on temperature and the active layer thickness of the LED.

Al-doped β-FeSi2 [β-Fe(Si1-xAlx)2] thin films with a thickness of 100 nm were epitaxially grown on Si(111) substrate by reactive deposition epitaxy (RDE). The reflective high-energy electron diffraction (RHEED) images showed epitaxial growth of β-Fe(Si1-xAlx)2 (101)(110)//Si(111) in the composition range of 0 < x < 2.3%. In high-resolution X-ray diffraction (HRXRD) measurements, the β(800) and β(406)(460) peaks shift to lower diffraction angles. The peak shifts linearly increase with Al composition. From an analysis of the peak shifts, Vegard's law of a, b, and c-axis in Al-doped β-FeSi2 was proven for the investigated Al-composition range. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Highly-insulating silicon oxide which contained hydrocarbon (CHn) groups (SiOCH) was deposited at room temperature by plasma-enhanced chemical vapor deposition using tetraethoxysilane. The carbon-rich SiOCH film deposited at 50W, 27 °C showed the high resistivity of 6 × 1015Ω cm at 0.5MV/cm. The insulating properties strongly depended on the deposition temperature and radio frequency (RF) power. The SiOCH films deposited at 300W, 53 °C showed the low carbon content and low resistivity due to the incorporation of hydroxyl (OH) groups generating electron traps. The room-temperature deposition at low RF power enabled the high-CHn addition, resulting in the suppression of OH incorporation into the films. The highly-insulating properties of the room-temperature deposited SiOCH originated from the suppression of OH incorporation.

Energy-transfer processes in Er,O-codoped GaAs (GaAs:Er,O) have been investigated by means of a pump and probe reflection technique. Time-resolved reflectivity exhibited a characteristic dip; a negative signal due to bandgap renormalization in less than 1 ps and then a gradual recovery. In the recovery process, there were two components, fast and slow. The fast recovery time (several ps) was inversely proportional to Er concentration. The analysis based on a rate equation indicated that it is due to the captare of electrons by charged traps. The slow recovery (30-60 ps) was well coincident with the time (54 ps) predicted theoretically in the fiamework of a multiphonon-assisted model. Optical excitation cross section of Er ions in GaAs: Er,O has also been studied in various samples and shown to depend strongly on Er concentration.

Dynamics of photoexcited carriers in Er-doped GaAs (GaAs:Er) and Er,O-codoped GaAs (GaAs:Er,O) have been systematically investigated by means of a pump and probe technique. A characteristic ps-scale relaxation was clearly observed in transient reflectance (dR/R) and transmission (dT/T) curves. The relaxation was due to the trapping of photoexcited carriers by an Er-related trap, which was closely related to efficiency of Er3+ luminescence.

Low-temperature plasma-enhanced chemical vapor deposition of amorphous carbon (a-C:H) films was investigated for surface passivation of carbon-doped silicon oxide (SiOCH) films. The a-C:H films were deposited using CH4 and Ar gases at 40–65°C. FT-IR results showed that the deposited films are a-C:H which incorporates hydrocarbon groups. In current−voltage measurements, the a-C:H showed a low leakage current of ~10–10 A/cm2 in air, indicating that the a-C:H films have a potential as a surface passivation layer to prevent moisture absorption in air. The insulating properties of room-temperature deposited SiOCH covered by the a-C:H strongly depended on radio frequency (RF) power in the SiOCH deposition. In the SiOCH film deposited at high RF power of 200 W, the resistivity in air was improved by the a-C:H passivation.

Ion-beam-synthesized β-FeSi2/Si interfaces were investigated by carrier-injection photoluminescence (CPL) measurements. The CPL intensity of Al-doped β-FeSi2/Si sample was larger than that of non-doped one. We obtained a carrier injection efficiency (γ) of γ = 0.41 in the Al-doped sample and γ = 0.19 in the non-doped one. These results revealed that Al-doping into β-FeSi2 is an effective technique for the improvement of β-FeSi2/Si interface which is defective due to ion implantation damages.

Carbon-doped silicon oxide (SiOCH) films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethoxysilane (TEOS) at low temperatures (27–53 °C). The structural and insulating properties of the films deposited with Ar or N2 plasma were investigated. In the deposition with low plasma density and low substrate temperature, both plasmas produced films with high hydrocarbon (CHn) content. The films prepared using Ar plasma showed a low leakage current of 7×10-10 A/cm2 at 1 MV/cm due to the incorporation of CHn groups, while the films with high CHn content prepared using N2 plasma showed poor insulating properties. The deposition using N2 plasma formed films with a defective structure, resulting in a higher etch rate than that of the films deposited with Ar plasma. The deposition with the low-density plasma of inert Ar gas is suitable for the low-temperature deposition of SiOCH films with high resistivity.

High-quality epitaxial Si films have been grown at low temperatures (500–600 °C) by atmospheric pressure plasma chemical vapor deposition (AP-PCVD) with a high growth rate (0.31 µm/min at 600 °C averaged over the 4-in. wafer). In contrast to the previous reports on other low-temperature CVD Si, the films in the present study are defect-free as observed by transmission electron microscopy and selective etching, and show no oxygen and carbon pileups at the film/substrate interface. To characterize defect-free epitaxial films with high sensitivity, we employed a photoluminescence (PL) method. When the epitaxial layer has better quality than the substrate, PL spectrum at 4.2 K mainly reveals the property of the substrate. On the other hand, room temperature PL measurements clearly show that the PL intensities of the surface-passivated epitaxial Si samples are much higher than that of Czochralski (CZ)-Si, which indicates a longer minority carrier recombination lifetime in the epitaxial Si layer than the bulk lifetime in CZ-Si.

A novel edge-light backlight unit using an optically patterned film (OPF backlight unit) for liquid crystal displays (LCDs) is composed of a light guide plate bonded to the top of fine lenses formed on the OPF, a diffusive sheet, a reflective sheet and a light source. A viewing-angle-dependent luminance distribution of the OPF backlight unit was controllable by changing the shape of a fine lens used for the extraction of light propagating through a light guide plate and the direction control of radiating light, and a luminance distribution in a radiation plane suitable for LCDs was realized by adjusting the interval between lenses. Moreover, the extraction efficiency of the OPF backlight unit was greater than that of a conventional backlight unit. Thus, the OPF backlight unit was shown to be promising for the realization of a brighter, lower power consumption, slimmer and lighter LCD than conventional LCDs.

GaAs epitaxial layers were grown by organometallic vapor phase epitaxy (OMVPE) using TEGa and TBAs over a wide range of growth temperature (350°C-700°C) and V/III ratio (2-9). GaAs with excellent surface morphology was obtained when the growth temperature was higher than 600°C. The GaAs surface tended to be rough with decreasing growth temperature below 550°C. When the growth temperature was decreased to 400°C, p-type GaAs was obtained with specular surface. The hole concentration increased with decreasing V/III ratio. The hole concentration was as high as 5.5×1017 cm–3 for the sample grown at 400°C with V/III ratio = 2.

Eu-doped GaN (GaN:Eu) has been identified as a promising red emitter. A GaN:Eu layer was confined in a microcavity consisting of a Ag mirror and an AlGaN/GaN distributed Bragg reflector (DBR), resulting in drastic enhancement of Eu emission intensity.

Magnetic properties of Er-doped GaAs (GaAs:Er) and Er,O-codoped GaAs (GaAs:Er,O) have been investigated by using superconducting quantum interference devices (SQUID) magnetometer at low temperature. In M-H curves of GaAs:Er,O, a characteristic magnetization due to the codoping with Er and O was observed at 2 K, while GaAs:Er exhibited much smaller magnetization. The saturation magnetization of GaAs:Er,O slightly increased with Er concentration. These results were discussed in relation to an atomic configuration formed selectively around Er3+ ions in GaAs:Er,O. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bulk β - FeSi 2 crystals were grown by annealing of unidirectionally solidified structures with rods of the e -FeSi in the α - FeSi 2 matrix. The crystallographic orientation of annealed samples was investigated by means of electron-backscattered pattern analysis. It was found that there were fibrous single crystals of β - FeSi 2 in the sample. The β - FeSi 2 crystal was easily grown along the solidification direction. The formation of the fibrous β - FeSi 2 single crystals resulted from limited nucleation at the initial stage.

Carbon-doped silicon oxide (SiOCH) thin films were deposited by room-temperature plasma-enhanced chemical vapor deposition (PECVD) using tetraethoxysilane (TEOS). The deposition rate and composition of the films strongly depended on radio frequency (RF) power. The films deposited at low RF power contained more CH n groups. The SiOCH films showed high etch rate and low refractive index in proportion to the carbon composition. The deposition with low plasma density and low substrate temperature is effective for SiOCH growth by PECVD using TEOS.

Dynamics of photo-excited carriers in Er,O-codoped GaAs have been systematically investigated by means of a pump and probe reflection technique. Time-resolved reflectivity exhibited an abrupt increase in amplitude, followed by a steep decrease to negative in less than 1 ps and then a gradual recovery. There were two components, fast and slow, in the recovery process. The fast recovery depended strongly on Er concentration and measurement temperature. The quantitative analysis indicated that the fast recovery corresponds to electron capture by a trap formed by Er and O codoping.

We have fabricated GaInP/Er,O-codoped GaAs (GaAs:Er,O)/GaInP double heterostructure (DH) light-emitting diodes (LEDs) and successfully observed 1.5 µm electroluminescence (EL) due to an Er-2O center under forward bias at room temperature. Er excitation cross section by current injection decreased with increasing GaAs:Er,O active layer thickness, implying reduced diffusion length of injected carriers in the active layer. Carrier dynamics in GaAs:Er,O have also been investigated by means of a pump and probe reflection technique. Time-resolved reflectivity of GaAs:Er,O exhibited a characteristic dip after a steep decrease to negative in less than 10 ps. The analysis of the characteristic dip revealed short lifetime in range of ps for photoexcited carriers. The extremely short lifetime is quite coincident with the reduced diffusion length of injected carriers, and suggests that a trap induced by Er and O codoping would play an important role in dynamics of nonequilibrium carriers in GaAs:Er,O.

The wide band-gap semiconductor, ZnO, has been proposed as one of the good host for Er3+ ions. In this investigation S was doped into the Er-containing ZnO specimens through the heat treatment in a H2S gas atmosphere. After sulfurization, the photoluminescence (PL) peak centered at 675nm from the ZnO host became much weaker, and accordingly the absorption peaks of Er3+ at 526nm, 550nm, and 665 nm became weaker. Also, the PL intensity around 1.54µm decreased after the sulfurization. However, when the sulfurized specimens were annealed at 1000oC in air, the PL intensity increased by about 3 times. The effects could be due to the modification of the local structure around the Er3+ ions in ZnO.

The electrical transport properties of β-FeSi2 epitaxial films grown on Si(001) or Si(111) substrates were investigated to clarify the growth-orientation dependence of the electrical conduction mechanism in the β-FeSi2 epitaxial films with low electron density of ∼1016 cm-3. As temperature was decreased, the transition from band conduction to hopping conduction was observed in both the epitaxial films. The β-FeSi2 on Si(111) film showed the transition at higher temperature than the β-FeSi2 on Si(001). When the epitaxial films were annealed, the transition temperature shifted to lower temperature. The β-FeSi2 on Si(001) film annealed at 800oC showed the largest electron mobility of 14800 cm2/V·s at 70 K. These results were understood by the conduction through the defect levels in the β-FeSi2 epitaxial films. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)