We systematically investigated the development of film morphology and crystallinity of methyl-ammonium bismuth (III) iodide (MA 3 Bi 2 I 9 ) through onestep spin-coating on TiO 2 -deposited indium tin oxide (ITO)/glass. The precursor solution concentration and substrate structure have been demonstrated to be critically important in the active-layer evolution of the MA 3 Bi 2 I 9 -based solar cell. This work successfully improved the cell efficiency to 0.42% (average: 0.38%) with the mesoscopic architecture of ITO/compact-TiO 2 /mesoscopic-TiO 2 (meso-TiO 2 )/MA 3 Bi 2 I 9 /2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′spiro-bifluorene (spiro-MeOTAD)/MoO 3 /Ag under a precursor concentration of 0.45 M, which provided the probability of further improving the efficiency of the Bi 3+ -based lead-free organic–inorganic hybrid solar cells.

A convenient two-step hydrothermal method was developed to synthesize water dispersible NaTaO3 nanoparticles. The growth of the NaTaO3 nanoparticles was retarded with the aid of a water soluble complex agent in the first step, such as citric acid, bicine, triacetin, and EDTA 2Na, which formed complexes with Ta5+. The sizes of the NaTaO3 nanoparticles, ranging from 5 nm to 30 nm, could be tuned by adjusting the reaction time as well as the complexing agent. An ultraviolet photodetector was fabricated with the solution processed NaTaO3 film as the active layer, which presented a sensitive response to 280 nm deep UV illumination with a light to dark current ratio of about 160 and a response time of about 50 ms.

Wide bandgap NaTaO3 nanocrystals (NaTaO3 NCs) were synthesized by a two-step hydrothermal method. The hybrid film based on the pyridine modified NaTaO3 NCs and 1, 3, 5-tri(m-pyrid-3-yl-phenyl) benzene (TmPyPB) was prepared by solution processing at room temperature. Photodetector based on the hybrid film presented selective sensitivity to UV signals with wavelength shorter than 317 nm because the bandgap wider than 4.0 eV. Under 5 mW/cm(2) 280 nm illumination through the semi-transparent Al cathode, a high ultraviolet signal-to-noise ratio of 3 orders of magnitude with response time about 200-300 ms can be achieved for the device in the case of -3 V bias. (C) 2015 Elsevier B.V. All rights reserved.

We demonstrate broadband optical quenching of photoconductivity in CdSe single nanowires with low excitation power. Using 1550-nm-wavelength light with 10-nW power for waveguiding excitation, we observe a typical responsivity of 0.5 A/W for quenching the photoconductivity established by 10-µW 660-nm-wavelength background light in a 403-nm-diameter CdSe nanowire, with detectable limit of the quenching power down to pW level at room temperature, which is several orders of magnitude lower than those reported previously. This large quenching effect originates from the enhanced light-defect interaction in the nanowires via waveguiding excitation. These results open new opportunities for noninvasive characterization of deep-level defect states in low-dimensional semiconductor nanomaterials, and novel optoelectronic applications of semiconductor nanowires such as high-sensitive broadband photodetection.

Polycrystalline aluminum nitride(AlN) thin film with c-axis preferred orientation was deposited on indium tin oxide(ITO) glass substrate by reactive radio frequency(RF) magnetron sputtering,which introduced a low temperature AlN interlayer as buffer layer.The deposited films were characterized by X-ray diffraction(XRD),atomic force microscopy(AFM) and field emission scanning electron microcopy(FESEM) to investigate the influence of the buffer layer on the crystalline quality and surface morphology.The results indicated that the introduction of the buffer layer tended to improve the crystallization of AlN films and meanwhile decrease the surface roughness from 19.1 nm to 2.5 nm,leading to a dense and smooth surface texture.The cross-sectional scanning electron microcopy(SEM) photographs of AlN films showed a high degree of alignment for the columnar structure.Furthermore,transmission spectra were studied to obtain the refractive index(2.018 7) and the extinction coefficient(0.007 7) of the deposited films.

Picosecond carrier dynamics of deep bandtail states (3.1 eV) in an unintentionally n-doped GaN epilayer at room temperature under high excitation densities (i.e., N0 = 1.0× 1019− 1.1× 1020 cm−3) have been investigated with nondegenerate femtosecond pump–probe (267/400 nm) reflectance (Δ R/R0). All Δ R/R0 traces possess a ∼2 ps buildup time that represents an overall time for the initial non-thermal carrier population to relax towards the continuum extremes and then into the probed tail states. We observe a saturation of Δ R/R0 initial (first 10 ps) recovery rate γi at a density of 5– 6×1019 cm−3 close to the Mott transition threshold obtained from time-integrated PL measurements. Such a saturation phenomenon has been identified as the trap-bottleneck due to the bandtail states and deep traps. As N0 is further increased, γi accelerates due to the onset of Auger recombination as the trap-bottleneck becomes effective. The best fit by the Auger model for N0 in the range of the mid-1019–1020 cm−3 yields an Auger coefficient of Ca∼ 5.0× 10−30 cm6 s−1.

Preferred c-axis oriented Sr0.6Ba0.4Nb2O6 (SBN60) thin films doped with different content of potassium ion have been fabricated by the sol–gel process on MgO(001) substrates. The micro-structure and surface morphology of the films were studied by X-ray diffractometer and atomic force microscopy. It is found that the crystalline properties and the refractive index of the SBN60 films are closely related to the potassium ion concentration in the films. The measured transverse electro-optic coefficient r51 of the SBN60 thin films with K+/Nb5+ molar ratios of 0, 1/7, 1/5, 1/3 and 2/3 are 36.85, 41.72, 43.11, 62.40 and 77.75 pm/V at 633 nm, respectively. An enhancement of r51 with K+ content in the SBN60 films has been clearly demonstrated.

利用溶胶-凝胶法在MgO(001)衬底上获得C轴择优取向的铁电铌酸锶钡(SBN)薄膜,主要介绍MgO(001)衬底上SBN60薄膜及掺入的K离子与Nb离子摩尔比例为1:3的SBN60薄膜横向电光系数r51的测量,实验测得不掺K的SBN60薄膜r51值为37.6 pm/V,掺K的r51值为58.5 pm/V.并由此设计一种基于MgO(001)衬底上的马赫-曾德尔型SBN60薄膜波导调制器,计算出在633 nm时,掺K比例为1:3的此种波导调制器半波调制电压值为10 V,不掺K的半波电压值为16 V,结果说明掺入K离子能增加薄膜的横向电光系数并有效的减少波导的半波调制电压.

Based on the difference of photonic band structures between TE and TM polarization modes in periodic multiplayer and the combining effect of one-dimensional (1D) hybrid dual-periodical photonic crystals (PCs), a novel method to design polarization band-pass filters used in wavelength division multiplexing system is presented. Such the polarization band-pass filters can be fabricated by dual-periodical TiO2/SiO2 thin film PC structures and theoretical calculation shows that they can have excellent optical properties with TM polarization transmission and TE polarization reflectance. And we try to physically discuss and explain the relation between the parameters of PC heterostructures and the optical characteristics of the filters, such as the number of TM polarization passbands, peak transmittance, half-band width and rejection and so on.

Highly oriented ferroelectric strontium barium niobate (Sr(0.6)Ba0.4Nb(2)O(6)) thin films were prepared on P-type Si(100) substrate by the Sol-Gel process. The XRD patterns of the SBN films show that SBN film prepared by using NbCl5, KOH as raw materials performed a highly c-axis preferred orientation perpendicular to the Si substrate, better than films that was prepared using Nb(OC2H5)(5) as starting agents. It may be duo to the existence of the potassium ion that not be filtered out completely during the preparation of the niobium alkoxide. The characteristics of D-F and C-V curves were obtained for SBN/Si film. The film exhibits high dielectric constant. In order to investigate ferroelectric characteristics further, the P-E loops of the SBN/Pt/Si were also measured. The films show better optical properties, transmittance of Sr0.6Ba0.4Nb2O6 films on MgO(001) and SiO2 substrates was more than 60 % at the range from 450 to 850nm, refractive index was measured to be 2.14 and 2.12 on the MgO and SiO2 substrate at 633nm respectively.

Room-temperature spectral and temporal behaviors of UV and visible emissions in ZnO epilayers grown onto (100) silicon substrates have been investigated by means of time-integrated and time-resolved photoluminescence(TIPL R TRPL). The PL lifetimes as short as 25-50 ps for the excitonic UV lines peaked at similar to 380 nm were found, indicative of ultrafast trapping of excitons by defects states inside the band gap. Compared to its as-grown precursor, the ZnO epilayer subjected to postgrowth thermal annealing in air showed enhanced intensities of both UV as well green emissions by nearly the same factor of -3.1, in accompany with complete disappearance of the impurity luminescence peaked at 2.83 eV. More importantly, the green luminescence in thepost-annealed ZnO was observed to decay as hyperbolic t(-1) and logarithmically shift its peakemission toward higher energies with increased excitation intensity, in excellent agreement with the tunnel-assisted donor-acceptor pair(DAP) recombination model. The possible mechanism of compensation between intrinsic impurities was also discussed.

High-quality z-axis oriented SBN60 thin films on MgO(001) substrates have been grown by sol-gel process, The transverse electro-optic coefficients r_(51) of the SBN60 and potassium ion doped SBN60 thin films were measured respectively. M-Z type waveguide modulators made of SBN60 thin films were designed. The half-wave modulation voltage was demonstrated to be decreased with the K ion doping.

Ferroelectric SrxBa1-xNb2O6 (0.2＜x＜0.8, SBN100 x＝ thin films of highly preferred c axis orientation have been grown on Si (100) substrate by the sol-gel method with post annealing at 1000°C. Investigated by x-ray diffraction and second ion mass spectrum,we observed that the SBN thin films prepared using NbCl5 precursor solution contained K+ ions, compared with Nb(OC2H5)5 precursored SBN films. By choosing appropriate contents of K+ there exists the optimum preferred orientation in SBN thin film.K ions dissolving in SBN cell and entering Si substrate can make SBN cell and Si cell a small twist simultaneously,which improves the matching of the film and the substrate to promote the high c axis superior growth.Finally,the optic characteristics of thin films have been tested.

Strontium barium niobate thin films on Si (001) substrates were obtained by sol-gel method. Highly c-axis oriented films were obtained by using the NbCl5 precursor instead of Nb(OC2H5)5-precursor, appropriate annealing temperature and introduction of buffer layer.

Dense and crack-free SBN thin films with the preferred c-axis orientation were successfully fabricated by the sol-gel method on Si(100) substrates with a MgO buffer layer. It was found that introducing the MgO buffer layer could effectively promote the formation of TTB SBN phase from SN and BN phases at lower temperature. Effects of annealing temperature and thickness of MgO buffer layer on the structural and morphological properties of SBN thin films were investigated. The SBN film with MgO buffer layer showed excellent epitaxy and densely packed grain morphology. The capacitance-voltage (C-V) properties of SBN films deposited on silicon substrates were found completely different from those of the films deposited on MgO-buffered silicon substrates, the C-V curves of SBN/Si films and SBN/MgO/Si films represent typical shapes of asymmetric and butterfly, respectively, indicating the improvement of the electrical properties and ferroelectric properties of the SBN films by introducing the MgO buffer layer.

The dynamics of carriers/excitons in as grown and annealed ZnO epilayers at room-temperature under high excitation densities were monitored by pump-probe(4.65/3.1 eV) differential reflectance transients on a time scale equal to 100 ps. The ΔR buildup showed a density-independent time delay of about 1.45 ps relative to the pump pulse, indicative of hot phonon effects, i.e., LO-phonon bottleneck, common to the as grown and annealed ZnO epilayers. Both appeared an initial fast ΔR decay with a time constant of about 20-25 ps due to rapid defect trapping. After the fast decay, the ΔR transient of the as grown ZnO became of sign reversal and turned to an induced absorption signal from defect levels with a decay time of several hundred picoseconds weakly dependent on excitation intensities. For the annealed ZnO, no change over in sign was observed on the slowly recovering component of ΔR, of which, in particular, the decay time was found to linearly depend upon carrier density. This finding, as confirmed by photoluminescence measurements, was attributed to a bimolecular recombination in terms of an exciton-exciton scattering in ZnO. These observations suggest that this unique pump-probe technique can provide a useful tool for understanding the defect physics of semiconducting materials.

By employing picosecond time-resolved photoluminescence, we investigated the temporal behavior of the near band-gap exciton emission located at ∼3.264 eV of a ZnO epilayer deposited onto a (1 0 0) silicon substrate by plasma-assisted MOCVD. The emission exhibits a biexponential decay behavior composed of an initial fast component (30–50 ps) followed by a second slower component (100–400 ps). The extracted time constant for the capture of free-excitons at the band-tail states is in the order of 30 ps. The results strongly suggest that the decay of the exciton population is governed by the initial fast decay due to the capture of excitons and trapping of carriers by deep centers at defects and/or impurities, and the measured slower decay component is due to the radiative recombination of free- or localized-excitons.

Femtosecond time-resolved reflectivity was used to investigate below-band-gap (3.1 eV) carrier dynamics in a nominally undoped GaN epilayer under high excitation. A 2.5-ps rising process can be observed in the transient trace. This shot rising time results from the hot phonon effects which can cause a delayed energy relaxation of the initial photocarriers toward the band edge. From the density dependence of the carrier dynamics, the Mott density was estimated to be 1.51-1.56×1019 cm-3. Below the Mott density, the initial probed carrier dynamics was explained to the effect of acoustic phonon-assisted tunnelling for localized states, where a significant excitation density dependence of the tunnelling probability was observed due to the optically induced bandtail extension to lower energies. Above the Mott density, the measured carrier dynamics reflected the relaxation of an electron-hole plasma, in which a distinct fast decay component of 2.3 ps was observed due to the onset of nonlinear relaxation processes such Auger recombination.

We report room-temperature time-integrated and time-resolved photoluminescence (PL) measurements on a nominally undoped wurtzite ZnO thin film grown on (001) silicon. A linear and sublinear excitation intensity Iex dependence of the PL intensity were observed for the 379.48-nm exciton line and the weak broad green band (∼510 nm), respectively. The green luminescence was found to decay as hyperbolic t−1, and its peak energy was observed to increase nearly logarithmically with increased Iex. These results are in an excellent agreement with the tunnel-assisted donor–deep-acceptor pair (DAP) model so that its large blueshifts of about 25 meV per decade increase in Iex can be accounted for by the screening of the fluctuating impurity potential. Also, the 30-ps fast decay of the exciton emission was attributed to the rapid trapping of carriers at luminescent impurities, while the short lifetime of τ1/e=200 ps for the green luminescence may be due to an alternative trapping by deeper centers in the ZnO. Finally, singly ionized oxygen and zinc vacancies have been tentatively invoked to act as donor–deep-acceptor candidates for the DAP luminescence, respectively.

A nominally undoped wurtzite ZnO thin film of highly c-axis orientation was successfully grown on (001) silicon by metal-organic chemical vapour deposition, and its photoluminescence was measured as a function of excitation intensity at room temperature. The ZnO sample exhibited a strong near band-edge (NBE) line at 379.48nm (3.267eV) and a weak broad green band around-510 nm (2.43eV), showing a linear and sublinear excitation dependence of the luminescence intensity, respectively. No discernible intensity dependence of lineshape and emission peak was found for the NBE line. On the other hand, the peak energy of the green luminescence was found to increase nearly logarithmically with the increasing excitation intensity. The above results clearly indicate that in the ZnO epilayer, the NBE line was due to an excitonic spontaneous emission, while the mid-gap green luminescence can be assigned to the tunnel-assisted donor-acceptor pair (DAP) radiative recombination.Moreover, we obtained an energy depth β-11.74 meV for the potential wells due to the fluctuating distribution of the unintentional impurities/defects responsible for the tunnel-assisted DAP emission.