TiO2 nanotubes have been now an attractive nanostructured material due to their unique opto-electronic catalytic ability, compatibility to particle materials and feasibility to fabricate. However, these advantages were usually limited by morphological and structural defects from the electrochemical anodization method. More detailed understandings of the tube formation process are also needed. We have systematically investigated the tube formation with varying conditions. Beside discovery of new nanosphere structure, we have systematically investigated the spontaneous oscillating phenomena in potentiostatic anodization of TiO2 tubes. Consequently, we have established a novel comprehensive physical and chemical method that effectively influences the morphology and structural properties of TiO2 nanotubes. With assistance of periodical anodic voltage and moderate mechanical stirring, the efficiency of dye sensitized solar cells (DSSCs) can be significantly enhanced. For instance, the efficiency of DSSC with small TiO2 islands in the anode can be 114% higher than the control sample. This method has also turned the efficiency of DSSC with TiO2 nanotubes by low temperature current annealing into announceable value (from 2.05% to 3.51%).
In this invited paper, we report the effect of different annealing environments on the changeable radiative recombination
characteristics of Si quantum dots (QDs), which not only provides ways to identify the photoluminescence mechanism,
but also realizes the possibility to control the origin of the luminescence. We also focus on the application of Si QDs in
the third-generation solar cells, with the emphasis on growth of well-ordered Si QDs, on photoresponse control of Si
QDs, and on approaches to reduce the lattice thermalization loss in Si QDs solar cells.
In this work, the influence of palladium addition on phase transition, surface morphology, structural, vibrational, and
electrical properties of nickel silicide is investigated at various temperatures. For Ni(Pd)Si films micro-Raman
measurements have yielded Raman phonon peaks belonging to NiSi phase, although redshifted, on par with new peaks at
322 and 434 cm-1, not determined before, which we assign to the compositional disorder, introduced by Pd. The results
have shown that Ni(Pd)Si films are thermally stable up to 900 °C, which is 100-150 °C more than that for pure NiSi
films. Applying Miedema's model we have calculated the heat of formation for Ni(Pd)Si and found it to be more
negative than that for pure NiSi, revealing a key role of Pd in the retardation of NiSi2 phase formation. AFM results have
shown that the presence of Pd favorably influences the surface morphology of NiSi, resulting in a smoother surface.
Furthermore, we have discussed the impact of annealing conditions on peculiarities of Pd diffusion, element distribution
and electrical properties of Ni(Pd)Si and NiSi films.
Wurtzite structure ZnMgO thin films with the energy gap (Eg) of 4.2 eV were deposited by oxygen-plasma enhanced
pulsed laser deposition (PEPLD) on quartz glass. Oxygen-plasma increases the Zn content in ZnMgO thin film, which
induced the evolution from cubic to hexagonal structure. The effects of target-substrate (T-S) distance on the band gap
and crystal quality of ZnMgO thin film deposited by PEPLD were studied by transmittance spectra and Raman. The
band gap of ZnMgO increased from 3.84 eV to 4.03 eV and the crystal quality decrease gradually when the T-S distance
decreased from 9 cm to 5 cm.
In this paper, we report the band offset and interface charge density properties of the nc-Si:H(n)/c-Si(p) heterojunction
(HJ) diode by the capacitance-voltage (C-V) measurement and theoretical modeling. By employing the ideal anisotype
HJ capacitance model and numerical C-V matching method, the band offset and heterostructure interface charge density
of the nc-Si:H/c-Si HJ have been obtained and analyzed. An interface charge density on the order of 1011 cm-2 is
estimated via the numerical C-V matching technique, and the low interface defect density has also been confirmed by the
frequency insensitive C-f results.
We have studied the weak localization (WL) effects in the electron accumulation layer on InN surface. Both the
spin-orbit relaxation time τso and the electron-phonon scattering time τe-ph have been extracted from the WL analysis.
We have observed that 1/τso increase with disorder and τe-ph exhibits a tendency to change gradually from the
characteristic dependence 1/τe-ph ∝ T3 in the pure case to the form of T2l-1 with increasing disorder.
X-ray absorption near-edge fine structure, optical transmission, and photoluminescence spectra have been measured on
an Al0.25In0.75N thin film. With the aid of a novel procedure developed for analyzing the transmission spectra, together
with a bandtail theory based on the calculation of density of occupied states and the carrier-phonon interaction, we have
obtained the temperature-dependent optical properties of the thin film, such as band gap and Urbach bandtail parameter.
Undoped and In-doped SrInxTi1-xO3(x=0, 0.1, 0.2) films have been deposited on Si(100) and quartz substrates by oxygen
plasma-assisted pulsed laser deposition (PLD). Effects of indium doping on the crystallinity and the optical energy band
gap of SrTiO3 (STO) films were investigated. Results indicate that undoped STO film is of rather good crystallinity and
low defects concentration. However indium doping deteriorates the crystallinity of the STO film, and results in the
roughening of the film surface. Moreover the a-axis length monotonically increases when increasing In content. For all
the films, the average transmission in the visible wavelength region (λ=400-800nm) is over 75%. The optical energy
band gap of STO thin films, measured from transmittance spectra, changes from 3.67eV to 3.93eV by indium doping.
We report on the photocurrent generated by nanometer grains embedded in hydrogenated amorphous silicon (a-Si:H), i.e.,
the hydrogenated nanocrystalline silicon (nc-Si:H) thin film. The embedded nanometer grains within the a-Si:H
boundaries are found to be a narrow continuous energy band in the a-Si:H band-gap, from which the transitions can
effectively generate the free electron-hole pairs, resulting in the observed high photocurrent. The high density of
nanometer Si crystals is a good means to improve the photo current response, and the fabrication of the low-cost infrared
photo detector by a single layer of nc-Si:H thin film on glass substrates is also expected.
We review our recently combined study of temperature-dependent photoluminescence, absorption, and photocurrent measurements with theoretical models on PbSrSe thin films grown by molecular beam epitaxy for the key properties of PbSrSe thin films and their microstructures. The derived empirical equations for band gaps, effective masses, and refractive indices have been employed successfully in PbSrSe/PbSe multiple quantum well (MQW) mid-infrared laser systems, which opens the way for the design of IV-VI MQW mid-infrared lasers. The infrared detection of PbSrSe thin films has been demonstrated at different temperatures, where the spectral intensity and wavelength coverage are determined by the band gap and the film thickness. The bias- and frequency-dependent capacitance characteristics have also been investigated in detail.
We review our recently combined study of temperature-dependent photoluminescence, absorption, and photocurrent measurements with theoretical models on PbSrSe thin films grown by molecular beam epitaxy for the key properties of PbSrSe thin films and their microstructures. The derived empirical equations for band gaps, effective masses, and refractive indices have been employed successfully in PbSrSe/PbSe multiple quantum well (MQW) mid-infrared laser systems, which opens the way for the design of IV-VI MQW mid-infrared lasers. The infrared detection of PbSrSe thin films has also been demonstrated at different temperatures, where the spectral intensity and wavelength coverage are determined by the band gap and the film thickness.
A novel concept to develop far-infrared (FIR) Si detectors is proposed based on homojunction internal photoemission. As the first approach, a 48 micrometers (lambda) c Si FIR detector is demonstrated on molecular beam epitaxy grown homojunction multilayers consisting of highly doped emitter layers and undoped intrinsic layers. The detector shows high responsivity over a wide wavelength range with a peak responsivity of 12.3 +/- 0.1 A/W at 27.5 micrometers and detectivity D* of 6.6 X 1010 cmHz1/2/W at 4.2 K. The (lambda) c and bias dependent quantum efficiency agree well with theory. Based on the experimental results and the model, Si FIR detectors (40 approximately 200 micrometers ) with high performance and tailorable (lambda) c can be realized using higher emitter layer doping concentrations.
The recent development of p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared (> 40 micrometers ) detectors for space application is reported. The emphasis is placed on the detector performance, which includes responsivity, quantum efficiency, bias effects, cutoff wavelength, uniformity, crosstalk, and noise. The results are promising and show that p-GaAs HIWIP detectors have high potential to become a strong competitor in far- infrared space applications.
A high performance, bias tunable, p-GaAs homojunction interfacial work function internal photoemission far-IR (FIR) detector has been demonstrated. A responsivity of 3.10 +/- 0.05 A/W, a quantum efficiency of 12.5 percent, and a detectivity D* of 5.9 X 1010 cm (root) Hz/W, were obtained at 4.2K, for cutoff wavelengths form 80 to 100 micrometers . The bias dependences of quantum efficiency, detectivity, and cutoff wavelength have been measured and are well explained by the theoretical models. The cutoff wavelength is modeled by a modified high density theory, and the quantum efficiency is predicted by scaling the free carrier absorption coefficient linearly with the doping concentration. The effect of the number of layers on detector performance and the uniformity of the detectors have been discussed. A comparison with Ge:GA photoconductive detectors suggests that a similar or even better performance may be obtainable.
A novel 48 micrometers cutoff wavelength ((lambda) c) Si far-IR (FIR) detector is demonstrated. Internal photoemission over a Si interfacial work-function of a homojunction consisting of molecular beam epitaxy grown multilayers is employed. The detector shows high responsivity over a wide wavelength range with a peak responsivity of 12.3 +/- 0.1 A/W at 27.5 micrometers and detectivity D* of 6.6 X 1010 cm (root) Hz/W at 4.2 K. The (lambda) c and bias dependent quantum efficiency agree well with theory. Based on the experimental results and the model, Si FIR detectors with high performance and tailorable (lambda) cs can be realized using higher emitter layer doping concentrations.
A high performance, bias tunable, p-GaAs homojunction interfacial workfunction internal photoemission far-IR detector has been demonstrated. A responsivity of 3.10 +/- 0.05 A/W, a quantum efficiency of 12.5 percent and a detectivity D* of 5.9 X 1010 cm (root) Hz/W, were obtained at 4.2K, for cutoff wavelengths from 80 to 100 micrometers . The bias dependences of quantum efficiency, detectivity, and cutoff wavelength have been measured and are well explained by the theoretical models, where the cutoff wavelength is modeled by a modified high density theory, and the quantum efficiency is predicted by scaling the free carrier absorption coefficient linearly with the doping concentration. The effect of the number of layers on detector performance and the uniformity of the detectors have been discussed. A comparison with Ge:Ga photoconductive detectors suggest that a similar or even better performance may be obtainable.
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