Magneto - Transport of electron symmetric and antisymmrtric states in highly doped InGaAs/InAlAs single quantum well

Beating patterns in longitudinal resistance caused by the symmetric and antisymmetric states were observed in a heavily doped InGaAs/InAlAs quantum well by using variable temperature Hall measurement. The energy gap of symmetric and antisymmetric states is estimated to be 4meV from the analysis of beating node positions. In addition, the temperature dependences of the subband electron mobility and concentration were also studied from the mobility spectrum and multicarrier fitting procedure.

Upconversion emission of a Er3+-doped glass microsphere under 633 nm excitation (vol 35, pg 353, 2004)

　

Preferred growth of nanocrystalline silicon in boron-doped nc-Si : H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2theta approximate to 47degrees and the exponent of crystalline plane of nc-Si in the film was (220). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B2H6) doping ratio in silane (SiH4), silane dilution ratio in hydrogen (H-2), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters. (C) 2004 Elsevier Ltd. All rights reserved.

Carrier transport assisted by dopants in doped poly(N-vinylcarbozole) light-emitting diodes

We have investigated the transient electroluminescence (EL) onset of the double-layer light-emitting devices made from poly(N-vinylcarbozole) (PVK) doped with 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and tris(8-hydroxy-quinoline) aluminium (Alq(3)). For the double-layered device in which PVK was doped with 0.1 wt% DCJTB, the EL onset of PVK lags that of DCJTB and Alq(3), while the EL onset of DCJTB and Alq(3) is simultaneous. However, the EL emission of the double-layered device of PVK/Alq(3) originates only from Alq(3). The results show that DCJTB dopants can not only help to tunnel electrons from Alq(3) zone to PVK but can also assist electrons transfer in PVK under high electric field by hopping between DCJTB molecules or from DCJTB to PVK sites at a low doping concentration of 0.1 wt%. When the DCJTB doping concentration is 4.0 wt%, the EL onset of Alq(3) lags that of DCJTB. The difference in the EL onsets of DCJTB, Alq(3) and PVK is attributed to the slow build-up of the internal space charge in the vicinity of the interface between PVK and Alq(3). The electron potential difference of the interface between Alq(3) and PVK doped by DCJTB can be adjusted by changing the DCJTB doping concentration in double-layer devices.

Optical properties of boron-doped Si nanowires

Raman scattering and photoluminescence (PL) of boron-doped silicon nanowires have been investigated. Raman spectra showed a band at 480 cm(-1), indicating that the crystallinity of the nanowires was suppressed by boron doping. PL taken from B-doped SiNWS at room temperature exhibited three distinct emission peaks at 1.34, 1.42. and 1.47 eV and the PL intensity was much stronger than that of undoped SiNWS. The increased PL intensity should be very profitable for nano-optoelectronics. (C) 2004 Elsevier B.V. All rights reserved.

Photoluminescence of Er-doped hydrogenated amorphous silicon nitride

Er photoluminescence (Er PL) and dangling bonds (DBs) of annealed Er-doped hydrogenated amorphous silicon nitride (a-SiN:H(Er)) with various concentrations of nitrogen are studied in the temperature range 62-300 K. Post-annealing process is employed to change the DBs density of a-SiN:H(Er). PL spectra, DBs density and H, N concentrations are measured. The intensity of Er PL displays complicated relation with Si DBs density within the annealing temperature range 200-500 degreesC. The intensity of Er PL first increases with decreasing density of Si dangling bonds owing to the structural relaxation up to 250 degreesC, and continues to increase up to 350 degreesC even though the density of Si DBs increases due to the improvement of symmetry environment of Er3+. (C) 2003 Elsevier B.V. All rights reserved.

Upconversion emission of a Er3+-doped glass microsphere under 633 nm excitation

In this work, The TBS glass microspheres doped with Er3+ for morphology-dependent resonances of upconversion emission were designed. The glass sample components are 25TiO(2)-27BaCO(3)-8Ba(NO3)(2)-6ZnO(2)-9CaCO(3)-5H(3)BO(3)-10SiO(2)-7water glass-3Er(2)O(3) (wt%), and the emission spectra of TBS glass and a TBS glass microsphere (about 48 mum in diameter) were measured under 633 nm excitation and discussed. The strong morphology-dependent resonances of upconversion luminescences in the microsphere were observed. The observed resonances could be assigned by using the well-known Lorenz-Mie Formalism. (C) 2003 Elsevier Ltd. All rights reserved.

A density-functional study of Al-doped Ti clusters: TinAl (n=1-13)

Equilibrium geometries, stabilities, and electronic properties of TinAl (n=1-13) clusters have been studied by using density-functional theory with local spin density approximation and generalized gradient approximation. The ground-state structures of TinAl clusters have been obtained. The resulting geometries show that the aluminum atom remains on the surface of clusters for n<9, but is slowly getting trapped beyond n=9, meanwhile, the Al atom exhibits a valent transition from monovalent to trivalent. The geometric effects and electronic effects clearly demonstrate the Ti4Al cluster to be endowed with special stability. The studies on the bonds indicate the change from ionic to metalliclike. (C) 2004 American Institute of Physics.

Growth of heavily Zn-doped InGaAs at low temperature by LP-MOCVD

Epitaxial growth of Zn-doped InGaAs on InP substrates has been carried out at 550degreesC by LP-MOCVD. Hole concentration as high as 6 x 10(19)cm(-3) has been achieved at the H-2 flow rate of 20 sccm through DEZn bubbler. The lattice constant of Zn-doped InGaAs was found to be dependent on the flow rate of DEZn, and the tensile strain mismatch increases with increasing H-2 flow rate of DEZn. The negative lattice mismatch of heavily Zn-dopped InGaAs may be due to, the small covalent bonding radius of zinc and the combination of butane from ethyl of DEZn,and TEGa. And the latter accelerates the pyrolysis of TEGa, which is the dominant mechanism in determining the negative mismatch of Zn-doped InGaAs. (C) 2003 Elsevier B.V. All rights reserved.

Mean-field study of Fe2+- and Co2+-doped diluted magnetic semiconductors

Based on a modified mean-field model, we calculate the Curie temperatures of Fe2+- and Co2+-doped diluted magnetic semiconductors (DMSs) and their dependence on the hole concentration. We find that the Curie temperatures increase with an increase in hole concentration and the relationship T(C)proportional to p(1/3) also approximately holds for Fe2+- and Co2+-doped systems with moderate hole concentration. For either low or high hole concentrations, however, the p(1/3) law is violated due to the anomalous magnetization of the Fe2+ and Co2+ ions, and the nonparabolic nature of the hole bands. Further, the values of T-C for Fe2+- and Co2+-doped DMSs are significantly higher than those for Mn2+-doped DMSs, due to the larger exchange interaction strength.

Synthesis and optical properties of europium-doped ZnS: Long-lasting phosphorescence from aligned nanowires

Quasi-aligned Eu2+-doped wurtzite ZnS nanowires on Au-coated Si wafers have been successfully synthesized by a vapor deposition method under a weakly reducing atmosphere. Compared with the undoped counterpart, incorporation of the dopant gives a modulated composition and crystal structure, which leads to a preferred growth of the nanowires along the [0110] direction and a high density of defects in the nanowire hosts. The ion doping causes intense fluorescence and persistent phosphorescence in ZnS nanowires. The dopant Eu2+ ions form an isoelectronic acceptor level and yield a high density of bound excitions, which contribute to the appearance of the radiative recombination emission of the bound excitons and resonant Raman scattering at higher pumping intensity. Co-dopant Cl- ions can serve not only as donors, producing a donor-acceptor pair transition with the Eu2+ acceptor level, but can also form trap levels together with other defects, capture the photoionization electrons of Eu2+, and yield long-lasting (about 4 min), green phosphorescence. With decreasing synthesis time, the existence of more surface states in the nanowires forms a higher density of trap centers and changes the crystal-field strength around Eu2+. As a result, not only have an enhanced Eu2+ -4f(6)5d(1)-4f(7) intra-ion transition and a prolonged afterglow time been more effectively observed (by decreasing the nanowires' diameters), but also the Eu2+ related emissions are shifted to shorter wavelengths.

Luminescence temperature and pressure studies of Zn2SiO4 phosphors doped with Mn2+ and Eu3+ ions

Zn2SiO4:Mn2+, Zn2SiO4:Eu3+ and Zn2SiO4:Mn2+ Eu3+ phosphors were prepared by a sol-gel process and their luminescence spectra were investigated. The emission bands from intra-ion transitions of Mn2+ and Eu3+ samples were studied as a function of pressure. The pressure coefficient of Mn2+ emission was found to be -25.3 +/- 0.5 and -28.5 +/- 0.9 meV/GPa for Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+ Eu3+, respectively. The Eu3+ emission shows only weak pressure dependence. The pressure dependences of the Mn2+ and Eu3+ emissions in Zn2SiO4:Mn2+ Eu3+ are slightly different from that in Zn2SiO4:Mn2+ and Zn2SiO4:Eu3+ samples, which can be attributed to the co-doping of Mn2+ and Eu3+ ions. The Mn2+ emission in the two samples, however, exhibits analogous temperature dependence and similar luminescence lifetimes, indicating no energy transfer from Mn2+ to Eu3+ occurs. (c) 2005 Elsevier B.V. All rights reserved.

Transverse magnetic field effect on the current hysteresis of doped GaAs/AlAs superlattice

The influence of a transverse magnetic field up to 13 T at 1.6 K on the current-voltage, I (V), characteristics of a doped GaAs/AlAs superlattice was investigated. Current hysteresis was observed in the domain formation regions of the I (V) at zero magnetic field while applied bias was swept in both up (0-6 V) and down (6-0 V) directions. The magnitude of current hysteresis was reduced and finally disappeared with increasing transverse magnetic field. The effect is explained as the modification of the current density versus electric field characteristic by transverse magnetic fields. Calculated results based on the tunnelling current formula in a superlattice support our interpretation.

Optical and magnetic properties of ZnS nanoparticles doped with Mn2+

ZnS:Mn nanoparticles of the cubic zinc blende structure with the average sizes of about 3 nm were synthesized using a coprecipitation method and their optical and magnetic properties were investigated. Two emission bands were observed in doped nanoparitcles and attributed to the defect-related emission of ZnS and the Mn2+ emission, respectively. With the increase of Mn2+ concentration, the luminescence intensities of these two emission bands increased and the ZnS emission band shifted to lower energy. Based on the luminescence excitation spectra of Mn2+, the 3d(5) level structure of Mn2+ in ZnS nanoparticles is similar to that in bulk ZnS:Mn, regardless of Mn2+ concentration. Magnetic measurements showed that all the samples exhibit paramagnetic behavior and no antiferromagnetic interaction between Mn2+ ions exists, which are in contrast to bulk ZnS:Mn. (c) 2005 Elsevier B.V. All rights reserved.

Structural, magnetic properties and photoemission study of Ni-doped ZnO

Nickel-doped ZnO (Zn1-xNixO) have been produced using rf magnetron sputtering. X-ray diffraction measurements revealed that nickel atoms were successfully incorporated into ZnO host matrix without forming any detectable secondary phase. Ni 2p core-level photoemission spectroscopy confirmed this result and suggested Ni hits it chemical valence of 2 +. According to the . We studied the electronic magnetization measurements, no ferromagnetic but paramagnetic behavior was found for Zn0.86Ni0.14O. We studied the electronic structure of Zn0.86Ni0.14O by valence-band photoemission spectroscopy. The spectra demonstrate a structure at similar to 2 eV below the Fermi energy E-F, which is of Ni 3d origin. No emission was found at E-A, suggesting the insulating nature of the film. (c) 2005 Elsevier Ltd. All rights reserved.