Controlling the electronic structure of SnO_2 nanowires by Mo-doping

Mo-doped SnO2 （MTO） nanowires are synthesized by an in-situ doping chemical vapour deposition method. Raman scattering spectra indicate that the lattice symmetry of MTO nanowires lowers with the increase of Mo doping, which implies that Mo ions do enter into the lattice of SnO2 nanowire. Ultraviolet-visible diffuse reflectance spectra show that the band gap of MTO nanowires decreases with the increase of Mo concentration. The photoluminescence emission of SnO2 nanowires around 580~nm at room temperature can also be controlled accurately by Mo-doping, and it is extremely sensitive to Mo ions and will disappear when the atomic ratio reaches 0.46%.

Structural, Optical and Electrical Properties of Li-doped ZnO Thin Films Influenced by Annealing Temperature

Li-doped ZnO thin films had been grown by radio frequency magnetron sputtering and then annealed under various annealing temperatures. The characteristics of ZnO films were examined by XRD, FESEM, Hall measurement and optical transmission spectra. Results showed that p type conduction was observed in Li doped ZnO films annealed at 500-600 ℃ and thep type ZnO films possessed a good crystalline with c-axis orientation, dense surface, and average transmission of about 85% in visible spectral region.

Influence of Ⅴ/Ⅲ ratio on the structural and photoluminescence properties of In_(0.52) AlAs/In_(0.53) GaAs metamorphic high electron mobility transistor grown by molecular beam epitaxy

A series of metamorphic high electron mobility transistors （MMHEMTs） with different Ⅴ/Ⅲ flux ratios are grown on CaAs （001） substrates by molecular beam epitaxy （MBE）. The samples are analysed by using atomic force microscopy （AFM）, Hall measurement, and low temperature photoluminescence （PL）. The optimum Ⅴ/Ⅲ ratio in a range from 15 to 60 for the growth of MMHEMTs is found to be around 40. At this ratio, the root mean square （RMS） roughness of the material is only 2.02 nm; a room-temperature mobility and a sheet electron density are obtained to be 10610.0cm^2/（V.s） and 3.26×10^12cm^-2 respectively. These results are equivalent to those obtained for the same structure grown on InP substrate. There are two peaks in the PL spectrum of the structure, corresponding to two sub-energy levels of the In0.53Ga0.47As quantum well. It is found that the photoluminescence intensities of the two peaks vary with the Ⅴ/Ⅲ ratio, for which the reasons are discussed.

Distinctive distribution of defects in CdZnTe:In ingots and their effects on the photoelectric properties

Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques.Samples cut from the head(T04)and tail(W02)regions of a crystal ingot show distinct differences in Te inclusion distribution.Obvious difference is not observed in Fourier transform infrared(FTIR)spectra,UV-Vis-NIR transmittance spectra,and I-V measurements.However,carrier mobility of the tip sample is higher than that of the tail according to the laser beam induced current(LBIC)measurements.Low temperature photoluminescence(PL)measurement presents sharp emission peaks of D^(0)X and A^(0)X,and relatively large peak of D^(0)X(or A^(0)X)/Dcomplex for T04,indicating a better crystalline quality.Thermally stimulated current(TSC)spectrum shows higher density of shallow point defects,i.e.,Cd vacancies,In^(+)_(Cd),etc.,in W02 sample,which could be responsible for the deterioration of electron mobility.

Aluminum incorporation efficiencies in A- and C-plane AlGaN grown by MOVPE

The aluminum incorporation efficiencies in nonpolar A-plane and polar C-plane A1GaN films grown by metalorganic vapour phase epitaxy （MOVPE） are investigated. It is found that the aluminum content in A-plane A1GaN film is obviously higher than that in the C-plane sample when the growth temperature is above 1070 ℃. The high aluminum incorporation efficiency is beneficial to fabricating deep ultraviolet optoelectronic devices. Moreover, the influences of the gas inlet ratio, the V/Ⅲ ratio, and the chamber pressure on the aluminum content are studied. The results are important for growing the A1GaN films, especially nonpolar A1GaN epilayers.

Structural and optical properties of AlN sputtering deposited on sapphire substrates with various orientations

AlN thin films were deposited on c-,a-and r-plane sapphire substrates by the magnetron sputtering technique.The in-fluence of high-temperature thermal annealing(HTTA)on the structural,optical properties as well as surface stoichiometry were comprehensively investigated.The significant narrowing of the(0002)diffraction peak to as low as 68 arcsec of AlN after HTTA implies a reduction of tilt component inside the AlN thin films,and consequently much-reduced dislocation densities.This is also supported by the appearance of E2(high)Raman peak and better Al-N stoichiometry after HTTA.Furthermore,the in-creased absorption edge after HTTA suggests a reduction of point defects acting as the absorption centers.It is concluded that HTTA is a universal post-treatment technique in improving the crystalline quality of sputtered AlN regardless of sapphire orienta-tion.

Growth and Characterization of Indium Doped Zinc Oxide Films Sputtered from Powder Targets

Indium doped Zn O films were grown on quartz glass substrates by radio frequency magnetron sputtering from powder targets. Indium content in the targets varied from 1at% to 9at%. In doping on the structure, optical and electrical properties of Zn O thin films were studied. X-ray diffraction shows that all the films are hexagonal wurtzite with c-axis perpendicular to the substrates. There is a positive strain in the films and it increases with indium content. All the films show a high transmittance of 86% in the visible light region. Undoped Zn O thin film exhibits a high transmittance in the near infrared region. The transmittance of indium doped Zn O thin films decreases sharply in the near infrared region, and a cut-off wavelength can be found. The lowest resistivity of 4.3×10^（-4） Ω·cm and the highest carrier concentration of 1.86×10^（21） cm^（-3） can be obtained from Zn O thin films with an indium content of 5at% in the target.

Electrochemical Impedance Spectroscopic Analysis of ZnS Nanorod Fabricated Using Butterfly Wings as Biotemplate

This article describes the growth of zinc sulfide（ZnS） nanorod on glass/aluminum foil by employing butterfly wings as biotemplate. Upon calcinating（at 400 °C）, the butterfly wings soaked in ZnS nanoparticle suspension, with uniform cage-like nanostructures in nanodimensions, were found on glass/aluminum surface. The transverse and longitudinal dimensions of the nanorods were evaluated from scanning electron microscopy micrographs as 132 and 159 nm,respectively. Purity of the ZnS nanorod found on the specimen was checked by recording XRD（28.877°, 48.038°, and57.174°） and Fourier transform infrared spectrometer spectra（663.7 and 551.68 cm^-1）. Luminescence natures of the nanorods were examined using photoluminescence spectral studies. The characteristic emission peak is shown in the visible region with strong intensity, while the excitation peak is shown at 267 nm. Electrochemical impedance spectroscopic analysis of ZnS nanorod exhibits double-layer capacitance value（Cdl= 6.7 nF）, and the Bode plot explains the stability of ZnS nanorod under the influence of electrical field.

Solvent-free Synthesis of Hexagonal Iron Sulfide Nanoflowers

Employing green and economic solvent-free synthesis route, hexagonal iron sulfide （Fe7Ss） nanoflowers were successfully synthesized for the first time. In the experiment, ferric hexadecylxanthate was used as the precursor, and hexagonal iron sulfide （Fe7Ss） nanoflowers were obtained by thermal decomposition of the precursor at 260 ~C without any additional solvent or inert gas protection. The as-prepared iron sulfide nanoflowers were characterized by means of X-ray diffraction （XRD）, transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and energy dispersive spectrometry （EDS）. The characterization results indicated that the nanoflowers had uniform size distribution with an average size of about 160 rim. The proposed strategy provides a possible general route for the synthesis of other metal chalcogenide nanostructures.

High infrared transmittance CdS single crystal grown by physical vapor transport

Φ55×15 mm~2 CdS bulk single crystal with high infrared transmittance was grown by physical vapor transport. The single crystal has a consistent structure from top to bottom, which was confirmed by X-ray diffraction. The(002) full-width at half-maximum of the X-ray diffraction was measured to be 60.00 arcsec, indicating a good quality of the structure. Hall mobility, specific resistivity, and carrier concentration for the top and bottom of the crystal were observed as well. Transmittance for the CdS single crystal was measured to be higher than 70% from 2.5 to 4.5 μm, making the single crystal an important candidate for infrared window materials. Furthermore,the absorption mechanism of the CdS single crystal was analyzed.

Photoluminescence investigation on highly p^+ -doped GaAs_(1-y)Sb_y(y<0.3)

Photoluminescence properties of highly p＋-doped GaASl_ySby are investigated. Band gap narrowing （BGN） effect is considered for heavily doped GaAs1_ySby epilayers. Band-gap Eg（GaAsl_ySby）=l.25y2-1.95y＋1.519 is obtained through fitting band-gap energy obtained by PL spectra from 35 to 300 K. Fermi level （El） and full width at half maximum （FWHM） of photolumines- cence increase with antimony mole fraction. The increase of Fermi level is attributed to hole mass of GaAsl_ySby decrease which is resulted from antimony composition increase. The increase of Fermi level means that more electrons participate in in- direct transition to result in FWHM increases.

Photoluminescence properties of ZnSe_(1-x)Te_x thin films on GaAs/ITO substrates by electron beam evaporation technique

Zinc chalcogenide which includes zinc selenide,zinc sulphide,zinc telluride and mixed crystals of these shows a great potential as an optoelectronic device material. Zinc selenotelluride is a suitable material for visible light emitting devices which are expected to cover the spectral range from yellow to blue. In our present study the composition controlled ZnSe1-xTex films with different Te content x = 0,0.2,0.4,0.6,0.8 and 1.0 were deposited by electron beam (EB) evaporation technique. GaAs films were deposited by vacuum evaporation route on indium tin oxide (ITO) substrates which were used as base for depositing the ZnSe1-xTex film. The band-gap energy change in the entire composition range was determined at room temperature by photoluminescence (PL) spectroscopy. The peak observed at about 2.56 eV shows the effect of solid solution formation between ZnSe and ZnTe which modifies the lattice and consequently the band edge emission characteristics. The heterostructures showed three peaks in the visible region of white light spectrum.

ZnCl_2-assisted Synthesis of ZnSe Polycrystal

A chemical-assisted element direct-reaction method is developed to synthesize ZnSe compound semiconductor material at a relatively low temperature （-1000 ℃）. ZnSe polycrystal was obtained in the closed-tube systems with Zn-Se, Zn-Se-Zn（NHa）2CI2, ZnoSe-NH4CI and Zn-Se-ZnCI2. The as-synthesized samples were tested by X-ray diffraction （XRD）, thermogravimetric analysis （TGA） and analyzed by thermodynamic numerical method. The results demonstrate that the synthesis efficiency is higher than 99.96% for Zn-Se-ZnCl2 system at around 1000 ℃ for 3 weeks. It also exhibits that not only temperature, but also low apparent ratio of volume and surface area of the source materials and higher ZnCl2 content are required to achieve high synthesis efficiency. A SeCI transporting reaction synthesis process is proposed based on the thermodynamic analysis.

AlGaSb/GaSb quantum wells grown on an optimized AlSb nucleation layer

Five-period AlGaSb/GaSb multiple quantum wells（MQW） are grown on a GaSb buffer.Through optimizing the AlSb nucleation layer,the low threading dislocation density of the MQW is found to be（2.50±0.91）×10~8 cm^（-2） in 1-μm GaSb buffer,as determined by plan-view transmission election microscopy（TEM） images.High resolution TEM clearly shows the presence of 90°misfit dislocations with an average spacing of 5.4 nm at the AlSb/GaAs interface,which effectively relieve most of the strain energy.In the temperature range from T = 26 K to 300 K,photoluminescence of the MQW is dominated by the ground state electron to ground state heavy hole（el-hhl） transition, while a high energy shoulder clearly seen at T76 K can be attributed to the ground state electron to ground state light hole（el-lhl） transition.