A new type of photoelectric response in a double barrier structure with a wide quantum well

We have calculated the photoelectric response in a specially designed double barrier structure. It has been verilied that a transfer of the internal photovoltaic effect in the quantum well to the tunnelling transport through above-barrier quasibound states of the emitter barrier may give rise to a remarkable photocurrent.

Photocurrent response in a double barrier structure with quantum dots-quantum well inserted in central well

We report the photocurrent response in a double barrier structure with quantum dots-quantum well inserted in central well. When this quantum dots-quantum well hybrid heterostructure is biased beyond + 1 or -I V, the photocurrent response manifests itself as a steplike enhancement, increasing linearly with the light intensity. Most probably, at proper bias condition, the pulling down of the X minimum of GaAs at the outgoing interface of the emitter barrier by the photovoltaic effect in GaAs QW will initiate the r,-X-X tunneling at much lower bias as compared with that in the dark. That gives rise to the observed photocurrent response. (c) 2006 Elsevier B.V. All rights reserved.

A sensitive NADH and glucose biosensor tuned by visible light based on thionine bridged carbon nanotubes and gold nanoparticles multilayer

A NADH and glucose biosensor based on thionine cross-linked multiwalled carbon nanotubes (MWNTs) and Au nanoparticles (Au NPs) multilayer functionalized indium-doped tin oxide (ITO) electrode were presented in this paper. The effect of light irradiation on the enhancement of bioelectrocatalytic processes of the biocatalytic systems by the photovoltaic effect was investigated.

INVESTIGATION OF THE PHOTOELECTRONIC PROPERTIES OF RARE-EARTH MONOPHOSPHIDES

The optical, electrical and photoelectronic properties of rare earth monophosphides (LnP, Ln = La, Nd, Sm and Y) have been studied. The experimental results indicate that their resistivities are low, the electric conduction in all of them is N-type, the energy gaps of LaP, NdP, SmP and YP are 1.46eV, 1.15eV, 1.1eV and 1.0eV, respectively. The SmP/Si and YP/Si junctions exhibit the photovoltaic effect. They may be used as photoelectronic sensors.

THE PHOTOELECTRIC PROPERTIES OF THIN-FILMS OF RARE-EARTH MONOPHOSPHIDES

The optical, electrical and photoelectric properties of rare earth monophosphides (LnP, Ln = La, Nd, Sm, Y, Dy and Yb) have been studied in thin films. The films exhibit semiconducting behaviour with energy gaps of 1.0-1.46 eV and n-type electrical conduction. Their resistivities are 10(-2) OMEGA-cm with corresponding Hall mobilities of 8.5-400 cm2 V-1 s-1. The films are deposited on a p-type silicon substrate in vacuum. Voltage-current characteristic measurements show that a p-n junction has been formed between LnP and silicon. Spectral sensitivity and a photovoltaic effect have been observed in LnP-Si junctions. They may be useful photoelectric materials.

The effect of interposing nanocrystalline Si(B) P plus layer on the photovoltaic properties of a-Si: H tandem solar cells

Tandem amorphous silicon solar cells have attracted extensive interest because of better performance than single junction counterpart. As n/p junctions play an important role in the current transportation of tandem solar cells, it is important to design and fabricate good n/p junctions.The properties of the n/p junction of amorphous silicon (a-Si) were studied. We investigate the effect of interposing a nanocrystalline p(+) layer between n (top cell) and p (bottom cell) layers of a tandem solar cell. The crystalline volume fraction, the band gap, the conductivity and the grain size of the nanocrystalline silicon (nc-Si) p(+) layer could be modulated by changing the deposition parameters.Current transport in a-Si based n/p ("tunnel") junctions was investigated by current-voltage measurements. The voltage dependence on the resistance (V/J) of the tandem cells was examined to see if n/p junction was ohmic contact. To study the affection of different doping concentration to the properties of the nc-Si p(+) layers which varied the properties of the tunnel junctions, three nc-Si p(+) film samples were grown, measured and analyzed.

Evaluating the effect of dislocation on the photovoltaic performance of metamorphic tandem solar cells

The photovoltaic conversion efficiency for monolithic GaInP/GaInAs/Ge triple-junction cell with various bandgap combination (300 suns, AM1.5d) was theoretically calculated. An impressive improvement on conversion efficiency was observed for a bandgap combination of 1.708, 1.194, and 0.67 eV. A theoretical investigation was carried out on the effect of dislocation on the metamorphic structure's efficiency by regarding dislocation as minority-carrier recombination center. The results showed that only when dislocation density was less than 1.6x10(6) cm(-2), can this metamorphic combination exhibit its efficiency advantage over the fully-matched combination. In addition, we also briefly evaluated the lattice misfit dependence of the dislocation density for a group of metamorphic triple-junction system, and used it as guidance for the choice of the proper cell structure.

The effect of annealing treatment on performance of interdiffused organic photovoltaic devices

We fabricated the interdiffused organic photovoltaic devices, which composed of poly (2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV) and buckminsterfullerene (C-60), by annealing treatment. After annealing, C60 diffused into the MEH-PPV layer, in consequence, MEH-PPV/C-60 interfacial area was increased and their interface became closer proximity. The results lead to reduce reverse-bias saturation current (J(s)), and increase the open-circuit voltage (V-OC) and the short-circuit current (J(SC)).

Effect of Poly (3-hexylthiophene) Nanofibrils on Charge Separation and Transport in Polymer Bulk Heterojunction Photovoltaic Cells

Crystalline poly (3-hexylthiophene) (P3HT) nanofibrils are introduced into the P3HT: [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) composite films via P3HT preaggregation in solution by adding a small amount of acetone, and the correlation of P3HT nanofibrils and the optoelectronic properties of P3HT:PCBM bulk heterojunction photovoltaic cells is investigated. It is found that the optical absorption and the hole transport or the resulted P3HT:PCBM composite films increase with the increase of the amount of P3HT nanofibrils due to the increased P3HT crystallinity and highly interconnected nanofibrillar P3HT networks. However, it is also found that high contents of crystalline P3HT nanofibrils may restrain PCBM molecules from demixing with the P3HT component that forms electron traps in the active layer. and hence reduce the charge collection efficiency. Small contents of P3HT nanofibrils not only improve the demixing between P3HT and PCBM components, but also enhance the hole transport via crystalline P3HT nanofibrillar networks, resulting in efficient charge collection.

Photovoltaic Properties and Quantum Size Effect in Nanocrystalline CeO2

Different size. nanocrystallines CeO2 were synthesized and their diffuse reflectance absorption spectra have heen measured. The absorption band in the region from 300 to 450 nm was assigned to the O2p-Ce2 4f transition. It was found that a strongly red-shifted broad continuum of the absorption band occured as the decrease of the partical size. We have also measured the surface photovoltage as function of wavelength by SPS technique. And the absorption band was resolved to two peaks with different photovoltaic properties. Photovoltaic quantum size effect was observed by FMSPS measurement.

Effect of lightly Si doping on the minority carrier diffusion length in n-type GaN films

We investigate the effects of lightly Si doping on the minority carrier diffusion length in n-type GaN films by analyzing photovoltaic spectra and positron annihilation measurements. We find that the minority carrier diffusion length in undoped n-type GaN is much larger than in lightly Si-doped GaN. Positron annihilation analysis demonstrates that the concentration of Ga vacancies is much higher in lightly Si-doped GaN and suggests that the Ga vacancies instead of dislocations are responsible for the smaller minority carrier diffusion length in the investigated Si-doped GaN samples due to the effects of deep level defects. (c) 2006 American Institute of Physics.

Optical investigation on the annealing effect and its mechanism of GaInAs/GaNAs quantum wells

Thermal annealing of GaInAs/GaNAs quantum wells (QWs) as well as other nitrogen- and indium-contained QW structures grown by molecular beam epitaxy and its effect on optical properties are investigated. The photoluminescence (PL) and photovoltaic (PV) spectra of annealed GaInAs/GaNAs QWs show that the luminescence properties become degraded due to the N diffusion from the GaNAs barrier layers to the GaInAs well layer. Meantime, the annealing-induced blueshift of the PL peak in this QW system is mainly induced by the change of In distribution, suggesting that the In reorganization is greatly assisted by the N-induced defects. The elucidation of annealing effect in GaInAs/GaNAs QW samples is helpful for a better understanding to the annealing effect in the GaInNAs/GaAs QWs. (C) 2003 Elsevier Science B.V. All rights reserved.

The investigations on semi-insulating GaAs by surface photovoltaic spectroscopy

The surface photovoltage (SPV) effect induced by the defect states in semi-insulating (SI) GaAs was studied. The PV response below the band edge was measured at room temperature with a de optical biasing. The spectra were found to be strongly dependent on the surface recombination and were attributed to formation of the carrier concentration gradient near the surface region, showing that SPV is a very sensitive and nondestructive technique for characterizing the surface quality of the SI-GaAs wafers.

Strong circular photogalvanic effect in ZnO epitaxial films

We report a strong circular photogalvanic effect (CPGE) in ZnO epitaxial films under interband excitation. It is observed that CPGE current is as large as 100 nA/W in ZnO, which is about one order in magnitude higher than that in InN film while the CPGE currents in GaN films are not detectable. The possible reasons for the above observations are the strong spin orbit coupling in ZnO or the inversed valence band structure of ZnO.