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Abstract: By increasing the content of Yb3+ ions from 20% to 98% in NaTm0.02Yb x Y0.98−x F4 (x=0.2−0.98) nanocrystals with size about 10nm, the intensities of near infrared (800nm) and blue (470nm) upconversion (UC) luminescence can be enhanced by orders of 45 and 49 times, respectively, under 970nm diode laser excitation. Pump power dependence illustrated that the 800 and 470nm radiations are still two- and three-photon processes, respectively. TEM imaging showed that the enhancement is not from the change of the crystal size. Steady-state equation and the measured lifetimes indicated that the enhanced 800nm radiations can induce the enhancement of the 470nm emissions, which is in good agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: Upconversion (UC) spectra of Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics were obtained under the excitation of a 976nm diode laser. Systematic experimental studies, including power dependence, luminescence lifetime, and the intensity ratio σ for the green to NIR emissions, were carried out in order to confirm the UC mechanism of Ho3+ ions. Our results demonstrated that the NIR emission was associated with the 5 F 4/5 S 2→5 I 7 transition of Ho3+ ions without the contribution of the 5 I 4→5 I 8 transition for Ho3+/Yb3+ codoped Y2O3 and Gd2O3 bulk ceramics. Additionally, population saturation in the 5 I 7 energy level had been observed in Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics. All experimental observations can be well explained by the steady-state rate equations. [ABSTRACT FROM AUTHOR]

Abstract: By self-consistently solving Schrödinger and Poisson equations, an extremely high two-dimensional electron-gas (2DEG) sheet density of 1.01×1014cm−2 is calculated in a novel InN-based InxGa1−xN/InN heterostructure field-effect transistor with an In content of x=0.1 and a doping level of Nd=1×1019cm−3 in the InxGa1−xN barrier layer. It is increased by almost one order of magnitude as compared to ∼1×1013cm−2 obtained in a conventional GaN-based Al0.2Ga0.8N/GaN heterostructure. With increasing In content of the InxGa1−xN barrier from x=0.05 to 0.15, the 2DEG sheet density decreases from 1.14×1014cm−2 to 0.91×1014cm−2 due to the decreased of polarization charges and the reduced conduction band offset. And the 2DEG density increases slightly with increasing doping level of the InxGa1−xN barrier. [Copyright &y& Elsevier]

In this paper, we took a brief investigation on the properties of two-dimensional electron gas (2DEG) in AlGaN/InGaN/GaN heterostructures. Band profiles and the 2DEG distribution were calculated by self-consistently solving the Schro¨dinger and Poisson equations. Our calculated results indicate that the 2DEG concentration can be considerably increased with the incorporation of an InGaN layer. Quantum confinement, and thereby the 2DEG distribution are very sensitive to the strain of the incorporated InGaN layer. Hence one can design the 2DEG by incorporating proper InGaN layer into the conventional AlGaN/GaN heterostructures. These novel features are attributed to the strong polarization effect in AlGaN/InGaN/GaN heterostructures. [Copyright &y& Elsevier]

In this paper, Al/AlN/Si(1 1 1) metal–insulator–semiconductor (MIS) structure has been fabricated and their interfacial properties have been investigated using capacitance–voltage techniques. The dielectric constant of AlN was found to vary from 5.01 to 8.67 with the frequency decreasing from 1 MHz to 50 Hz due to the existance of a transition zone between AlN and Si substrate which is not forbidden to the electronics. The distribution of the interface states in the interface was extracted from the frequency-dependent capacitance–voltage characteristics of the MIS structure. The interface state density Dit in the silicon forbidden band gap was in the order of 1012 eV−1 cm−2 and the time constant was about 10−5 s through analyzing the capacitance as a function of frequency. [Copyright &y& Elsevier]

3C-SiC was heteroepitaxially grown on Si(1 1 1) substrates by the low pressure chemical vapor deposition (LPCVD) with a gas mixture of silane, ethane and hydrogen. Under the very low pressure of 30 Pa, we got good single-crystalline SiC films at a low temperature of 900 °C, much lower than the typical deposition temperature above 1200 °C found elsewhere. Their characteristics and crystallinity were examined by X-ray diffraction, infrared absorption, and auger electron spectrum (AES). The SiC peak was found at a 2θ value of 35.8°. The full width at half maximum (FWHM) is only 0.28°, indicating that the SiC film is single crystalline. In the FTIR absorption a peak at 800 cm−1 is observed. In the AES depth profile the film is composed of Si and C with a composition very close to that of stoichiometric SiC. The surface morphology of the film was examined by AFM. These images show the good crystalline of SiC at the surface, and the surface image of a film grown at the initial stage was also observed in order to study the growth mechanism at low temperature and low pressure. [Copyright &y& Elsevier]

In this letter, we investigate the carrier features in AlGaN/InGaN/GaN heterostructure field-effect transistors. A study of charge control in the AlGaN/InGaN/GaN structure is performed by self-consistently solving Schrödinger's equation in conjunction with Poisson's equation. The results indicate that the concentration of two-dimensional electron gas can be largely increased with the incorporation of an InGaN layer. Both carrier density and quantum confinement are very sensitive to the strain in the InGaN channel layer. These novel features are attributed to the strong polarization effect in the AlGaN/InGaN and InGaN/GaN interfaces. [ABSTRACT FROM AUTHOR]

Room-temperature photoluminescence spectra of Mg-implanted GaN grown on sapphire by low-pressure metal-organic chemical vapor deposition have been studied. An obvious blue emission and a broad yellow-band emission were observed. Spectra analysis suggests that, in the forbidden band of GaN, there exist four doping-related energy levels at 170 meV and 310 meV below the conduction band, and at 250 meV and 390 meV above the valence band, respectively. Transitions between these energy levels give the blue emission of 415 nm and 438 nm. Also, annealing partially recovers the GaN crystalline structure, leading to the reappearance of the yellow-band luminescence. [ABSTRACT FROM AUTHOR]

The two-dimensional electron gas distribution in AlGaN/GaN high electron mobility transistors is determined from the solution of the coupled Schrödinger’s and Poisson’s equations. Considering the piezoelectric effect, the two-dimensional electron gas concentration is calculated to be as high as 7.7×10[sup 19] cm[sup -3] . In order to obtain an understanding of how the two-dimensional electron gas distribution is influenced by dopants in GaN, we observed the two-dimensional electron gas concentration and occupation of sub-bands versus dopant concentration in the GaN layer of an AlGaN/GaN heterostructure. Our results show that the two-dimensional electron gas concentration is slightly increased at higher doping levels in GaN, while the quantum confinement in the AlGaN/GaN heterostructure is weakened with the increase of donor concentration in the GaN layer. [ABSTRACT FROM AUTHOR]

Investigates the higher order bands (HOB) in irradiated Czochralski silicon. Use of Fourier transform infrared absorption spectroscopy and Hall-effect measurements; Factors attributing to the creation of higher order bands; Photoexcitation and decay characteristics of HOB and the thermal donors.

The strained Si layer has been grown on the relaxed 3C–SiC virtual substrate by a hot-wall low-pressure chemical vapor deposition (LPCVD) system. The relaxed SiC virtual substrate was grown on Si(1 1 1) substrate by LPCVD and the crystal quality of the layer is characterized by X-ray diffraction and Fourier transform infrared absorption spectroscopy. It is apparent to find three regions in the Auger electron spectroscopy depth profile graph of the sample, which refer to the cap Si layer, the relaxed 3C–SiC virtual substrate and the Si(1 1 1) substrate, respectively. The bonding states of the relaxed 3C–SiC virtual substrate in the sample are analyzed by X-ray photoelectron spectroscopy. The Raman spectra of the sample indicate the cap Si layer is strained. A high hole Hall mobility value of 889 cm2/V s (300 K) is obtained in the strained Si layer, which is due to the in-plane compressive biaxial strain in this layer. [Copyright &y& Elsevier]

Spin splitting of the two-dimentional electron gas (2DEG) in modulation-doped Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures has been studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The spin splitting is observed in Shubnikov–de Haas oscillations at a magnetic field higher than 5.4 T and a temperature of 1.4 K. The effective g factor g[sup *] is enhanced due to the exchange interaction of the 2DEG at high densities. The ratio of the transverse effective g factor g[sub ⊥][sup *] and the longitudinal effective g factor g[sub ∥][sup *] is g[sub ⊥][sup *]/g[sub ∥][sup *]=2.6 indicating the large difference between g[sub ∥][sup *] and g[sub ⊥][sup *]. It is demonstrated that the anisotropy of the g[sup *] is due to the strong polarization-induced electric field at the heterointerface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cubic silicon carbide (3C-SiC) has been grown on Si (111) substrate by chemical vapor deposition. The crystal quality of SiC with the SiCN buffer layer is obviously improved comparing with that grown on the SiC buffer layer. The SiCN film, composed of elemental Si and SiC 1-x N x alloy, is formed by the constant-source diffusion of the C and N atoms into the Si substrate. During the 3C-SiC high temperature growth, this in-situ formed SiCN film evolves into a double sub-layered SiCN buffer, including the SiC 1-x N x alloy and the SiCN composite sub-layers. The SiC 1-x N x alloy layer ( x from 0 to 0.09) results from the limited-source diffusion of N from the in-situ formed SiCN film to the subsequently deposited SiC. The SiCN composite layer, composed of elemental Si and SiC 1-x N x alloy ( x from 0.09 to 0.06), is caused by the constant-source diffusion of C from the SiC towards the substrate, as well as the outgoing diffusion of N in the in-situ formed SiCN film. The SiCN buffer layer can effectively accommodate the lattice mismatch between SiC and Si substrate. [ABSTRACT FROM AUTHOR]

The SiCN film, which has the same crystal structure as 3C-SiC verified by X-ray diffraction and Raman scattering, has been formed on Si (111) substrate by constant-source diffusion using a chemical vapor deposition system. Via X-ray photoelectron spectroscopy, the film has been identified as the mixture of elemental Si and SiC 1 − x N x alloy, with the SiC 1 − x N x content decreases from 87.4% to 17.9% and the mole fraction x increases from 0.17 to 0.21, as the depth extends from the near surface to the interface. The measured composition distribution can be well explained by the constant-source diffusion model, confirms that the formation mechanism of the SiCN film is the diffusion of C and N into the Si substrate. This provides a new method for fabricating crystalline SiCN thin films. [ABSTRACT FROM AUTHOR]

The Al 0.22 Ga 0.78 N/GaN/Al 0.22 Ga 0.78 N multilayer heterostructure photoconductive detectors were designed and fabricated. The influence of AlGaN/GaN interface polarization fields on the properties of the photodetector was investigated. The energy band profile of the heterostructure was approximately calculated. Results indicate that electron and hole wells exist on the GaN sides of the Al 0.22 Ga 0.78 N/GaN/Al 0.22 Ga 0.78 N interfaces. The existence of two-dimensional electron gas was proved by variable temperature Hall measurements. The spectral response shows that the responsivity of the heterostructure photodetector was as high as 43 00 A/W at 355 nm under 3 V bias, which is nearly ten times higher than that of a GaN monolayer structure photodetector. [ABSTRACT FROM AUTHOR]

Magnetointersubband scattering (MIS) oscillations of two-dimensional electron gas (2DEG) in Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures have been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. Double periodic Shubnikov–de Haas oscillations modulated by MIS oscillations have been observed due to the intersubband scattering of the 2DEG at the two lowest subbands in the triangular quantum well at the heterointerface. By using the fast Fourier transform analysis, it is found that the MIS oscillations become slightly weaker with an increase in temperature. From the MIS frequency, the energy separation between the first and the second subbands is determined to be 80 meV. The observation of the MIS effect indicates that the effective masses of the electrons in the first and second subbands are the same in Al[sub 0.22]Ga[sub 0.78]N/GaN heterostructures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) with p-hBN layer are investigated numerically. In comparison with the conventional AlGaN DUV LEDs, the proposed LED can significantly improve the carrier injection, radiative efficiency, as well as the electroluminescence (EL) intensity under the same applied forward bias. Simultaneously, the light extraction efficiency in the LED using p-hBN instead of p-AlGaN exhibits a more than 250% increase at the applied voltage of 7.5 V due to the smaller loss of reflection and absorption of the emitted light. [ABSTRACT FROM AUTHOR]

Abstract: The AlGaN-based deep ultraviolet light-emitting diodes (UV LEDs) with specific design of staggered AlGaN quantum wells are investigated numerically. The proposed UV LEDs with Al0.45Ga0.55N–Al0.5Ga0.5N–Al0.45Ga0.55N and Al0.5Ga0.5N–Al0.45Ga0.55N–Al0.5Ga0.5N staggered quantum well layers exhibit significant improvement for the light output power and carrier injection efficiency compared with the conventional AlGaN UV LED. The enhanced performance of the designed LEDs is explained by the simulated distribution of carrier concentration, radiative recombination rate and wave function overlap in the quantum wells. [Copyright &y& Elsevier]

Highlights: [•] A nanoporous InGaN/GaN multiple quantum wells has been fabricated. [•] The overall external quantum efficiency for nanoporous InGaN/GaN MQWs is enhanced. [•] The nanoporous structure led to more light scattering and lower defects density. [Copyright &y& Elsevier]

Abstract: InGaN/GaN single quantum well (SQW) structures under various InGaN growth temperatures have been grown by metal organic chemical vapor deposition (MOCVD), the surface morphologies and optical properties are investigated. The radius of the typical V-pits on the SQW surface is affected by the InGaN well-temperature, and the surface roughness decreased as the well-temperature reduced. Room-temperature photoluminescence (PL) and cathode luminescence (CL) shows the quantum well and quantum dot (QD)-like localized state light emission of the SQWs grown at 700 and 690°C, respectively, whereas the samples grown at 670 and 650°C present hybrid emission peaks. Excitation power dependent PL spectra indicates the QD-like localized state emission dominates at low excitation power and the quantum well emission starts to take over at high excitation power. [Copyright &y& Elsevier]

Abstract: Selective area epitaxy has been applied to grow GaN stripe templates with side facts, followed by InGaN/GaN multiple quantum well (MQW) structures. Stripes oriented along the direction of [11−20] form smooth triangular {1−101} facets, while stripes in the [1−100] direction produce incomplete coalesced {11−22} side facets with planar (0001) surface under the same growth conditions. Room-temperature luminescence property is investigated by using photoluminescence (PL) and cathodeluminescence (CL) spectra. It is found that uniform emission at 400nm has been obtained for triangular MQWs oriented the direction of [11−20]. With respect to the MQWs grown along the [1−100] direction, large redshift is achieved for the ridge area compared to the sidewall due to the lateral vapor diffusion and surface migration. [Copyright &y& Elsevier]

Abstract: The effect of alloying and expitaxial mismatch strain on the surface ultraviolet (UV) emission efficiencies of AlxGa1−xN films, pseudomorphically grown on both c- and m-plane AlyGa1−yN templates (x−0.03+1.79x−0.06x2 (0

Abstract: Impact of anisotropic strains on low-frequency dielectric properties and room-temperature polar phases of SrTiO3 epitaxial thin films is investigated. The dielectric properties show a remarkable change as a function of anisotropic strains. The number of room-temperature polar phases is as twice as that of isotropically strained SrTiO3 thin films. [Copyright &y& Elsevier]

Abstract: The strong correlations between the O/Zn ratio and carbon impurity incorporation have been observed on the ZnO films grown using N2O or O2 as oxygen source in metal-organic chemical vapor deposition (MOCVD). From in-situ mass spectrometric measurements, the O/Zn ratio in the MOCVD reactor is found to decrease to a minimum value as the growth temperature increased till a critical growth temperature T c, and then increased above T c due to different dissociation rates of the oxygen and Zn sources. The strongest D and G modes, which are ascribed to carbon clusters sp2 related modes, have been observed in Raman scattering spectroscopy for the ZnO samples grown at T c, indicating the highest incorporation rate of carbon impurity in the samples grown at T c. Compared with O2, N2O has a low dissociation rate and that leads to a lower value of O/Zn ratio, resulting in much stronger D and G modes and higher incorporation rate of carbon impurities in the samples grown at T c. It is interesting to note that the lowest specific resistances from Hall effect measurements were also obtained on the samples grown at T c, indicating possible electrical contributions from the formation of carbon clusters, which should be highly conductive regions in ZnO. Furthermore, ionization or addition of H2 in the case of N2O can significantly enhance the dissociation of N2O, with film quality improved significantly. This study shows that a high O/Zn ratio is critical to suppress carbon impurity incorporation and to grow high quality ZnO by MOCVD, especially at low growth temperature. [ABSTRACT FROM AUTHOR]

Abstract: We have grown Fe3N films on GaN(0002) substrates by metalorganic chemical vapor deposition (MOCVD). Under lower growth temperatures, small iron particles were formed on GaN surface, while under higher growth temperatures, Fe3N films were formed. The surface morphology of samples with different growth temperatures were characterized by atomic force microscopy. In X-ray Photoelectron Spectroscopy (XPS) measurement, the coexistence of metallic Fe and Fe2+ or Fe3+ was observed in the sample grown at 600°C, while the sample grown at 1050°C showed only high valence forms of Fe ions. It was also found that the magnetic moments of Fe3N prefer to align normal to the c-axis. [Copyright &y& Elsevier]

Abstract: By solving Schrödinger and Poisson equations self-consistently for Al x Ga1−x N/GaN heterostructures grown along the axis, the spatial distribution of electrons and the energy of all the bound states confined in heterostructures are obtained, and electrons are found to occupy the first two subbands. Considerable magnitude of the Rashba spin splitting for the first two subbands at the Fermi level is obtained. Changes of the Rashba spin splitting with the Al composition in the barrier are calculated. The effect of electrons taking up more than one subband on the Rashba spin splitting for the first subband is discussed. Individual factors contributing to the Rashba spin splitting are discussed in detail, and the contribution to the Rashba coefficient from the well and the heterointerface are found to be much more than that from the barrier. The results show that a high density of the 2DEG and the internal electric field caused by the piezoelectric polarization and the spontaneous polarization are crucial for considerable Rashba spin splitting for Al x Ga1−x N/GaN heterostructures. [Copyright &y& Elsevier]

Abstract: A sizable spin-dependent photocurrent related to the interband transition in InN films is observed. The surface charge accumulation layer is suggested to be the origin of the circular photogalvanic current, which is consistent with the result of uniaxial strain experiments and the comparison of front and back incidence. The homogeneous photocurrent demonstrates the existence of spin splitting in the InN surface layer, and the structure inversion asymmetry (SIA)-dominant mechanism indicates a great possibility for the manipulation of spin splitting, which would undoubtedly benefit further research and applications of spintronics. [Copyright &y& Elsevier]

Abstract: The biocompatibility of a kind of heat-treated bilayer hydroxyapatite (HA) coatings with nano-particles was investigated, mainly in terms of the immersion in simulated body fluid (SBF) and osteoblast adhesion. Scanning electron microscopy (SEM) was used to observe the morphology of coatings and cellular adhesion. The phases present in the coatings were determined by X-ray diffraction (XRD). Calcium ion (Ca2+) concentration in SBF was measured by Atomic absorption spectrophotometer. The results show nano-HA heat-treated at 650°C for 0.5h (BBCs) is comparatively stable during immersion in SBF and favor of the adhesion of osteoblasts. Cellular filopodia adhere firmly to the nano-particles and stretch in various direction. [Copyright &y& Elsevier]

Abstract: The alloy Al x Ga1− x N was grown by metal-organic chemical vapor deposition (MOCVD) using a high-temperature AlN interlayer on a thick GaN template. The Al composition (x) of the Al x Ga1− x N was varied in the range 0.13⩽x⩽0.8. The in-situ reflectance spectra indicate that the growth process of AlGaN alloys is dominated by trimethylgallium (TMGa) molar flux when the molar flux of trimethylaluminium (TMAl) is kept constant. The Al compositions and growth rates of AlGaN alloys were determined by Rutherford backscattering, which indicates that the incorporation efficiency of TMAl is improved remarkably by decreasing the TMGa molar flux. The crystalline quality of these AlGaN alloys is evaluated by measuring the symmetric (002) and asymmetric (102) ω-scan X-ray diffraction peak widths. The best crystalline quality, among these Al x Ga1− x N alloys, is for an Al composition of x=0.54 where the full-width at half-maximums of the AlGaN (002) and (102) diffraction peaks are 265 and 797arcsec, respectively. This conclusion is consistent with the surface morphology of the AlGaN alloys probed by atomic force microscopy. Room temperature cathodoluminescence spectra show pronounced near band edge emission from these AlGaN alloys. The optical band gaps (E g) are found to deviate from linear interpolation between E g GaN and E g AlN with a bowing parameter b=0.89. [Copyright &y& Elsevier]

Abstract: N-doped p-type ZnO (p∼1018cm-3) was grown on sapphire(0001) substrate by metal-organic chemical vapor deposition method. Ni/Au metal was evaporated on the ZnO film to form contacts. As-deposited contacts were rectifying while ohmic behavior was achieved after thermally annealing the contacts in nitrogen environment. Specific contact resistance was determined by circular transmission line method and a minimum specific contact resistance of 8×10−4 Ωcm2 was obtained for the sample annealed at 650°C for 30s. However, Hall effect measurements indicate that, as the rapid thermal annealing temperature increased up to 550°C or higher the samples’ conductive type have changed from p-type to n-type, which may be due to the instability nature of the present-day p-type N-doped ZnO or the dissociation of ZnO caused by annealing process in N2 ambient. Evolution of the sample''s electric characteristics and the increment of metal/semiconductor interface states induced by rapid thermal annealing process are supposed to be responsible for the improvement of electrical properties of Au/Ni/ZnO. [Copyright &y& Elsevier]

Abstract: In this letter, we report on the realization of the p-type ZnO film by in situ nitrogen doping and subsequent thermal activation, as well as the discussions on the doping mechanism. Through the high temperature activation, a conversion of conductivity from n- to p-type with a hole concentration of ∼1019/cm3 has been observed by Hall measurements, accompanied with the formation and dissociation of N–H complex investigated by Raman spectra. These observations provide probability on the passivation effect of N–H complex and dehydrogenation process at high temperature, as confirmed by the variation of N and H atomic concentration in the secondary ion mass spectra. The dehydrogenation process in oxygen ambient at 900°C led to the dissociation of NO–H complexes, resulting in the formation of isolated NO acceptors and compensation to the intrinsic donor-like defects. The N-related acceptor bound exciton in photoluminescence with a small binding energy of 100meV and high p-type conductivity in activated ZnO:N film imply the important role of dehydrogenation effect to the realization of p-type ZnO. [Copyright &y& Elsevier]

Abstract: In this paper, hydrogenated amorphous silicon nitride (a-SiN x :H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effect of NH3 flow rate R on the deposition rate, structure and luminescence were studied using various techniques such as optical emission spectroscopy, Fourier Transform Infrared absorption (FTIR), X-ray photoelectron spectroscopy (XPS) and fluoro-spectroscopy, respectively. Optical emission behavior of SiH4 +NH3 plasma shows that atomic Si radical concentration determines the film deposition rate. Structural transition of a-SiN x film from Si-rich one to near-stoichiometric/N-rich one with R was revealed by FTIR and the two phase separation of a-Si and a-Si3N4 was also convinced in Si-rich SiN x films by XPS. Either photo- or electroluminescence for all the SiN x films with R >3 sccm shows a strong light emission in visible light wavelength range. As R <6 sccm, recombination of electrons and holes in a-Si quantum dots is the main mechanism of photo/electroluminescence for Si-rich SiN x films, however, for photoluminescence, gap states'' luminescence is also in competition; as R >6 sccm, light emission of the SiN x film originates from defect states in its band gap. [Copyright &y& Elsevier]

Abstract: The circular photogalvanic effect (CPGE) is observed in InN at inter-band excitation. The function of the CPGE induced current on laser helicity is experimentally demonstrated and illustrated with the microscopic model. A spin-dependent current obtained in InN is one order larger than in the AlGaN/GaN heterostructures at inter-band excitation. The dependence of CPGE current amplitude on light power and incident angle can be well evaluated with phenomenological theory. This sizeable spin-dependent current not only provides an opportunity to realize spin polarized current at room temperature, but also can be utilized as a reliable tool of spin splitting investigation in semiconductors. [Copyright &y& Elsevier]

Abstract: The fluid dynamics of a vertical metal-organic chemical vapor deposition (MOCVD) reactor for the growth of ZnO film have been studied. The relevant transport equations were solved by numerical integration using a finite volume difference method. Computation results show that the deposition rate strongly depends on the operating parameters of the MOCVD reactor. Simulation results show that the reactor pressure has effect on the deposition rate, which becomes larger with the increment of the reactor pressure in the range of low pressure in our study. The simulated deposition rate is observed to increase firstly and then decrease with the main carrier gas flow rate. The computational study demonstrates that the distance between the O2 inlet and substrate in the vertical MOCVD reactor plays a key role to obtain a balance between the deposition rate and the uniformity of films across the substrate. The optimization of the MOCVD operational parameters has been applied in the MOCVD growth of high-quality ZnO epilayers. [Copyright &y& Elsevier]

Abstract: High reflectivity (>93.5%) distributed Bragg reflectors (DBRs) have been successfully produced using the AlGaN/AlN multilayer stacks materials system by metal-organic chemical vapor deposition (MOCVD). The peak reflectance of the DBRs was located at 320nm. The nominal Al composition is 30%, and the layer thicknesses of the different periods stack were designed for a target wavelength of 330nm. We present reflectivity, SEM, AFM and XRD data of Al x Ga1− x N/AlN Bragg reflectors grown on (0001)-oriented sapphire. The surface of the AlN/AlGaN DBRs was found to grow in quasi-two-dimensional (2D) mode, which was indicated by the atomic force microscopy (AFM). The DBR has very smooth surface and the interface was distinct. [Copyright &y& Elsevier]

Abstract: This paper reports the high mobility InN film grown by MOCVD with GaN buffer layer on sapphire substrates. Different buffer layers are used in our experiments. These buffer layers included the annealing sapphire substrate, the low-temperature GaN layer (LT-GaN), the high-temperature GaN layer (HT-GaN) and the complex buffer layer with HT-GaN on LT-GaN. The crystalline quality of the InN film is sensitive to the underlying buffer layer when the film is grown under the high effect V/III ratio condition. And the growth conditions are optimized in our system. We employed the three-step buffer layer with HT-GaN and LT-GaN on annealing sapphire. The mirror like layers on 2in sapphire wafers was obtained. The structure, optical and electrical characteristics of InN was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), photoluminescence (PL) and IR optical absorption. The PL and the absorption studies of the materials reveal a marked energy band gaps structure around 0.70eV, at room temperature. The uniformity of morphology and the electrical property of the grown InN film are markedly improved by using the complex buffer layer with HT-GaN and LT-GaN on the annealing sapphire. The InN film grown by this buffer layer has the carrier concentration of 3.9×1018 cm−3 and the Hall mobility of 939cm2/Vs. [Copyright &y& Elsevier]

Abstract: AlN/Al0.3Ga0.7N distributed Bragg reflectors (DBRs) are grown on sapphire (0001) by metal-organic chemical vapor deposition (MOCVD). The number of stacks of the DBRs varies between 6 and 30. The thickness of the quarter-wave layers is designed such that the target peak reflectance locating at the wavelength of 330nm. The GaN or AlGaN templates are employed for growing the AlN/AlGaN DBRs. It is found that the templates intensively influence on the surface roughness and the interfacial properties of AlN/AlGaN DBRs. The result of atomic force microscopy indicates that the AlN/AlGaN DBRs grow on GaN template under quasi-two-dimensional mode. And the good interfaces of AlN/AlGaN not only clearly observed by cross-sectional scanning electron microscopy, but also concluded from narrow width and high orders of satellite peaks detected by high-resolution X-ray diffraction. The peak reflectance of 20 stacks DBRs on GaN template reaches up to 82% located at 326nm.While those DBRs grown on AlGaN template do not show such structural and optical properties due to the rough surface of AlGaN template and the poor interfaces of AlN/AlGaN. [Copyright &y& Elsevier]

Abstract: We have grown single crystalline GaMnN films by a horizontal hydride vapor-phase epitaxy (HVPE) system. The structures and crystal quality were confirmed by XRD and Raman scattering measurements. The structure analysis indicated that we obtained uniform GaMnN solid-solution films; the Mn atoms were substituted for Ga sites and did not form Mn precipitates or clusters. The superconductor quantum interference device (SQUID) results show that the GaMnN films without the phase separation exhibit paramagnetic properties. [Copyright &y& Elsevier]

Abstract: Zn1− x Ni x O (, 0.02 and 0.05) powders were prepared by a sol–gel method. We have studied the structure and magnetic properties of the samples by using X-ray diffraction (XRD), Raman scattering, superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS). The SQUID results showed that all the samples exhibit ferromagnetism above room temperature. From the XRD spectra of the samples, it was obvious that there had no second phase while the Ni-doped concentration was lower than 5at%. Raman spectra showed an additional band, which is related to the vibration of Ni dopant. The EXAFS was used for the Ni K-edge to probe the local structures of the Ni dopant in ZnO, which show that Ni dopant was substituted for Zn atoms position up to 5at% Ni concentration. [Copyright &y& Elsevier]

Abstract: Structural and optical properties of a-SiN x films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) have been investigated. The Fourier transform infrared (FTIR) spectroscopy shows the structural evolution of the SiN x films, which are defined as Si-rich SiN x and N-rich SiN x films, also confirmed by Raman spectroscopy. The origin of the light emission for SiN x films may be attributed to two mechanisms, i.e., quantum confinement effect (QCE) and transition of defect energy levels. The correlation between light emission and structures of SiN x films is discussed. [Copyright &y& Elsevier]

Abstract: High-quality single-crystal Ga-doped ZnO films have been epitaxially deposited on (0002) sapphire substrate by low-pressure metal organic chemical vapor deposition (MOCVD) technique. The dependence of structural, electrical and optical properties of films on Ga doping concentration was investigated. As grown at the Ga/Zn gas ratio of 3.2at%, the film shows a narrow linewidth of 0.26° for ZnO (0002) peak, high carrier concentration of 2.47×1019 cm−3, and high optical transparency over 90%. The carrier concentration increased sharply and became saturated at higher doping level due to the onset of carrier compensation. The Burstein–Moss blueshift of the absorption edge energy increased as expected with the carrier concentration up to 2.47×1019 cm−3. In addition, doping-induced photoluminescence (PL) emission linewidth broadening and bandgap renormalization (BGR) effects have also been observed. The intensity of PL emission decreased with increasing Ga dopant concentration, which was believed to be a direct consequence of the doping-enhanced nonradiative recombination rates. [Copyright &y& Elsevier]

Abstract: Indium nitride films, grown at 375 °C by low-pressure metal–organic chemical vapor deposition, have been annealed at temperatures ranging from 400 °C to 475 °C under an ambient ammonia atmosphere. According to our X-ray diffraction spectra of the annealed InN films, the integrated intensity of the InN (0002) diffraction peak reaches its minimum value at the temperature of 425 °C, but the full-width at half maximum of the InN (0002) peak shows an opposite change with the annealing temperature. These results indicate that the InN film annealed at 425 °C has the worst structural quality. Scanning electron microscope and X-ray photoelectron spectroscope measurements demonstrate that as the annealing temperature is increased to 425 °C, the density of indium grains on the surface increases greatly due to the volatilization of nitrogen atoms. Above 425 °C, the density of the indium grains begins to decrease, resulting from the desorption of indium. The indium grains formed during this annealing process are then supposed to be responsible for the degraded structural quality in the annealed InN. [Copyright &y& Elsevier]

The ZnO films were grown by low pressure metal-organic chemical vapor deposition (LP-MOCVD) using dimethylzinc (DMZn) and oxygen. The as-grown film has strong (0002) oriented characteristic, containing the chain-like network grains in small sizes, A well-resolved shoulder emission at 3.03 eV in the photoluminescence (PL) spectra has been ascribed to the interstitial zinc in the crystal, implying a serious oxygen deficiency state of the MOCVD growth, in good agreement with the analysis of XPS results. Post-annealing of the films leads to the remarkable improvement of the structure, morphology, components and optical properties. Large hexagonal columnar grains were then observed by atomic force microscope (AFM). The luminescence efficiency was enhanced greatly due to the reduction of the nonradiative defects. Meanwhile, chemisorbed oxygen gives rise to surface acceptor states, resulting in the different radiative recombination. Photoluminescence excitation measurement shows good agreement with the above conclusions. [ABSTRACT FROM AUTHOR]

Abstract: IIIV x N1−x ternary alloys are promising materials for their applications in light-emitting devices in the range of wavelength from ultra violet to the infrared ray due to the large bowing of band gap energy. In this paper, molecular dynamical method was used to calculate the solubility of phosphorus in GaN by using the Gibbs free energy and the dielectric theory. The calculation results show that the content of P in GaN varies with the growth temperature, which may be larger than 25% in the N-rich GaP x N1−x or less than 90% in the P-rich GaP x N1−x , at the growth temperature of about 1500K. We compared our theoretical results with those reported in references. By using light-radiation heating together with low-pressure metal-organic chemical vapor deposition, and ion implantation techniques, we have successfully synthesized N-rich (x &#60;0.17) and P-rich GaP x N1−x (x >0.90) compounds. [Copyright &y& Elsevier]

Abstract: We study the effect of generation and amplification of confined acoustic phonons by drifting electrons in an embedded quantum wire. A general formula for the phonon amplification coefficient α has been derived. Our calculations show that the quantum wire structure can be used for electrical generation of an intense high-frequency coherent phonon flux. The amplification coefficients of the order of cm−1 can be achieved in the sub-THz range for the example of Si0.5Ge0.5 quantum wires embeded in Si. [Copyright &y& Elsevier]

Quantum and transport scattering times related to different subbands in modulation-doped Al0.22Ga0.78N/GaN single quantum wells (SQW) have been studied by magneto- transport measurements. The quantum scattering time related to the first and the second subbands is determined to he 0.078 ps and 0.088 ps, respectively, at 1.5 K. Results indicate that the scatterings from heterointerface and ionized donors at both side of GaN well are all important in limiting quantum scattering time. By using mobility spectrum technique the transport scattering time related to the first subband is determined to he 0.128 ps. Transport-to-quantum scattering time ratio in the first subband is 1.6. It is concluded the large angle scatterings play a very important role in limiting quantum scattering time in this SQW. [ABSTRACT FROM AUTHOR]

The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal-organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the (0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to he 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer. [ABSTRACT FROM AUTHOR]

Abstract: Indium nitride (InN) films have been deposited on sapphire substrates at 350–500 °C using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). Increasing the growth temperature changes the structure of InN from cubic to hexagonal. At 500 °C, no InN can be grown on sapphire due to its decomposition. The X-ray diffraction (XRD) spectra of InN films show that the diffractions from In(101) reach a maximum at 425 °C and begin to decrease at the growth temperature higher than 425 °C. According to the scanning electron microscope (SEM) images of InN films, the In aggregation on the surface is observed at the growth temperature of 425 °C, which corresponds to the most intensive diffraction of In(101) in XRD spectra. In addition, the density of InN nucleation sites is reduced by increasing the growth temperature. As well as the increase of In desorption with the growth temperature, the decrease of InN nucleation sites are responsible for the most significant In aggregation at 425 °C. [Copyright &y& Elsevier]

Mn-doped films were grown in an ammonia-source HVPE system. Mn3GaN0.5 and GaN were detected in film samples without other phase when the HCl–Mn/NH3 ratio range from 1/200 to 1/100. (GaxMn1-x)N phase also formed in films. Two broad bands centered at 305 and 674 cm-1and new peaks at wave numbers of 592 cm-1arised in Raman spectra of Mn-doped films. It was also found that A1(LO) modes of all Mn-doped samples were strongly asymmetric and showed a considerable redshift. Mn-doped films showed an obvious hysteresis loops at room temperature. Mn-doped films showed metallic characteristic and this mixed structure may be greatly beneficial to spin injection magnetotransport devices. [Copyright &y& Elsevier]

Time characteristics have been simulated numerically both for n- and p-channel memory based on Ge/Si hetero-nanocrystals. Owing to the advantages of the staircase potential barrier and the higher band offset on valence band, the retention time of the memory could achieve the increase of several orders while the programming time still hold the same order approximately, compared with the memory based on Si nanocrystals. Therefore, the present memory device would be expected to solve the contradiction between high-speed programming and long retention time. If so, this type of device would be a promising non-volatile memory for future VLSI. [Copyright &y& Elsevier]