Search

The thickness of the CdS:O window layer plays an important role in CdTe-based thin-film solar cell performance. Normally with thinner CdS:O layer, the cells’ short wavelength response can be enhanced to achieve higher short-circuit current density (Jsc), while the open-circuit voltage (Voc) and fill factor (FF) would degrade. Previous research finds that reducing the CdS:O layer thickness to less than 40 nm would decrease the cells’ efficiency (Eff.). In this work, 18% efficiency CdTe thin-film solar cell with only 30 nm CdS:O window layer is demonstrated. A post annealing process is developed to fabricate high efficiency cells with ultrathin CdS:O layers. Our results indicate that the high defect density in CdTe absorber, low built-in potential (Vbi) and high back contact barrier (Φb) are partially responsible for the reduced Voc and FF of cells with ultrathin CdS:O layers. The post annealing process can increase the carrier concentration (NCV) and Vbi, and decrease the Φb, in which way improves Voc and FF for higher cell efficiency.

Optical detection of pressure has the advantage of direct and dynamic indication of the pressure distribution with a high spatial resolution. In this study, microcrystal (µ-crystal) light-emitting ...

We present broadband MMI couplers, developed for a novel integration platform on InP with active/passive integration capabilities for the 1300nm wavelength range. Low loss (

In this work, etched singlemode-multimode-singlemode (E-SMS) optical fiber structures are evaluated through the implementation of anti-BSA/BSA immunoassay. By tracking the wavelength response, it is found that the E-SMS devices can detect the presence of antiBSA.

We succeeded in hydrogen evolution using InGaN photocatalysts grown on conductive Ga2O3 substrates. These photocatalysts exhibited a conversion efficiency of 0.8% from incident light energy to stored H2 chemical energy. Their quantum efficiency was determined to be more than 1% at 404 nm by incident photon-to-current conversion efficiency (IPCE) measurement. We found that the wavelength response of the InGaN structure can be extended to the visible region. These results indicate that the conductive Ga2O3 substrates are suitable for the photocatalysts.

Ga 0.51 In 0.49 P solar cells with compositionally-graded (Al z G a1-z )xln 1-x P window-emitter structures, both lattice-matched and pseudomorphically (tensile) strained, were grown via molecular beam epitaxy using a digital alloy based grading approach. Preliminary results suggest that the resulting drift field and elimination of discrete interfaces near the top surface of these devices helps mitigate the impact of surface/interface recombination and sub-optimal window and/or emitter material quality. A significant increase (>10% absolute quantum efficiency) in carrier collection in the UV-blue (λ < 500 nm) was observed, along with a commensurate Jsc increase of ~10% relative versus standard, fixed-composition reference cells.

Based on the combined effect of mapping more than one resonant wavelength response to microwave frequency, a tunable flat-top bandpass microwave photonic filter is implemented by a single microring resonator and single sideband modulation.

Holograms as spectrum splitting concentrator elements are achieving high relevance in improving overall efficiency of photovoltaic systems. Photopolymer holographic elements have the added advantages of near hundred percent diffraction efficiency, easy recording and handling, lower cost etc. Along with high diffraction efficiency, achieving optimum spectral response is of critical importance here. This paper reports recording of volume holographic elements of 91% optimum diffraction efficiency at 639 nm and the spectral and angular response studies conducted.

We propose and demonstrate a 1times2 thermooptic digital optical switch with variable optical attenuators that are integrated with the S-bend waveguides connecting the output of the Y-switch with a standard fiber array. With a total heating power of 140 mW applied to the switch, we have achieved less than -42-dB optical crosstalk. The wavelength response of the switch is flat across the entire C-band. The average polarization-dependent loss of the switch is about 0.49 dB

A novel Frequency Selective Surface (FSS) conflguration is proposed for the design of polarization-insensitive metamaterial absorbers operating below 1GHz, where the flrst resonances of small commercial enclosures appear. The novel FSS shows a strong sub- wavelength response, enhanced by the dielectric substrate, which allows the design of compact planar absorbers with excellent angular and polarization stability.

In recent times, the transportation industry has generated a number of developments involving new technology in signaling. Important developments have involved the production of light by means of light emitting diode (LED). The optical proprieties of LEDs depended on junction temperature. Since the heat from the junction must be dissipated into the ambient somehow, changing the ambient temperature affects the junction temperature and hence the emitted light. When the LEDs have been used in the railway or traffic signals, the optical proprieties of these have to maintain more rigorous color specifications. Besides, the limits imposed must be respected in ample range of variation of the ambient temperature (typ. 233-347K). The peak wavelength of LED shifts proportionally to changes in junction temperature. Therefore, to respect color specifications with signals using LED as light source it is not simple. In this paper, we describe problems of the temperature dependent changes of colorimetrical parameters of LEDs. Besides we will introduce a method through which to build a correct signal with feedback that, according to the measured temperature, it reacts to correct the optic characteristics of signal.

In this work we report on the optimization of the p-GaN window layer for InGaN/GaN solar cells. We studied the effect of p-GaN thickness and growth temperature on the electrical performance. By optimizing the window thickness of In x Ga 1−x N solar cells with X In ≈0.04 we maximized short wavelength response and produced solar cells with 82% FF and Voc of 2 V and enhancement of Jsc of 80% over un-optimized devices. We also studied the effect of growth temperature of the window layer, and found that the electrical performance was greatly improved with higher growth temperatures. By increasing the p-GaN growth temperature from 890 °C to 1040 °C, reverse bias leakage was reduced by three orders of magnitude, Voc increased from 0.85 to 1.65 V and peak output power increased by nearly 100% for devices with X In ≈0.08. Surface pit density was also significantly decreased by increasing growth temperature and seems to be an important mechanism for leakage in these devices.

The effect of filter characteristics on the output performance of actively mode-locked fiber ring lasers has been studied experimentally and numerically, with the same 3-dB bandwidth, the filter that has a flatter wavelength response tends to generate narrower soliton-like pulses.

Around 1920, Case investigated the thallium sulfide photoconductor - €”one of the first photoconductors to give a response in the near IR region to approximately 1.1 I¼m. The next group of materials to be studied was the lead salts (PbS, PbSe, and PbTe), which extended the wavelength response to 7 I¼m. PbS photoconductors from natural galena found in Sardinia were originally fabricated by Kutzscher at the University of Berlin in the 1930s. However, for any practical applications it was necessary to develop a technique for producing synthetic crystals. PbS thin-film photoconductors were first produced in Germany, next in the United States at Northwestern University in 1944, and then in England at the Admiralty Research Laboratory in 1945. During World War II, the Germans produced systems that used PbS detectors to detect hot aircraft engines. Immediately after the war, communications, fire control, and search systems began to stimulate a strong development effort that has extended to the present day. After 60 years, low-cost, versatile PbS and PbSe polycrystalline thin films remain the photoconductive detectors of choice for many applications in the 1-€“3 I¼m and 3-5 I¼m spectral range. Current development with lead salts is in the FPAs configuration.

A new scheme to obtain wavelength-insensitive optical fibre couplers, based on group velocity equalisation, is presented. It allows flattened wavelength response over the whole C-band.

A design idea of extended blue NEA GaAs photocathode is given in this paper. A new structure is presented by changing the composition of GaAlAs in grads in order to get the short wavelength response and in the same time to reduce the stress in the photocathode material, so that an extended blue GaAs photocathode with a higher sensitivity of image intensifier can be obtained. Finally, the spectrum responses of both ordinary and extended blue GaAs image intensifier are given, the relationship of material structure and the result of blue extending is discussed.

We demonstrate the first In0.53Ga0.47As/InP p‐doped quantum well infrared photodetector (QWIP). This detector has the shortest wavelength response, λp=2.7 μm, ever achieved in a QWIP and operates at normal incidence.

We propose and experimentally demonstrate a novel method which, for the first time to our knowledge, makes it possible to tailor the wavelength response of a waveguide grating coupler. Such grating couplers may be used to improve the efficiency of broad-band quantum-well infrared photodetectors and solar cells.

The effect of surface recombination velocity on the short wavelength response of the tandem junction solar cell is investigated theoretically. The analysis predicts approximately the same dependence of the short-circuit current on surface recombination velocity as for a conventional p-n junction solar cell. It is concluded that the experimentally observed improvement in the blue response of the tandem junction solar cell is probably due to a small surface recombination velocity as a result of the absence of front-surface metallization.

Recently developed 3-5 compound semiconductor photocathodes show promise of substantial advantages over conventional photocathodes in increased yield and longer wavelength response. This paper reviews the physical principles of operation, preparation, and activation of these new types of photocathode. Also discussed are current fabrication techniques, problem areas, practical difficulties, and operating characteristics of experimental cathodes.

Achieving both high resolution and high read/write efficiency has been tried with a rather thick single-pole-head film core having the sensitive (ordinary) trailing edge and the less sensitive leading edge in the neighborhood of which a degradation of the magnetic flux density (Bs) is made. The degradation is made by laminating several sputtered layers of different alloy constitution of Co 1-x Zr x (x = 0.17-0.32). The whole film core consists of this degradation region of 4.2 μm thick and high permeability Co 0.85 Zr 0.03 Nb 0.12 region of 5.0 μm thick. Observed shallowing of the reproduce nulls in the wavelength response with the rather thick core shows a possible compatibility of the resolution and the efficiency.

We report In1−xGaxAsyP1−y/InP photodiode detectors with external quantum efficiencies of 50–70% without antireflection coating. The short‐ and long‐wavelength response limits of these very efficient detectors can be compositionally tuned to lie anywhere in the wavelength range 0.9

Barium ferrite media have created a lot of interest for digital and analog applications because of their potential to achieve high recording densities. To fully exploit this potential, it is necessary to develop media with good perpendicular orientation and to employ high saturation narrow gap heads. It is possible, however, to obtain very good recording performance utilizing Ba‐ferrite media which are nonoriented or only partially oriented and ordinary ferrite heads for high‐density digital recording applications. In this study, we investigated the performance of such media in rigid disk form using conventional and narrower gap ferrite heads, and obtained much better short wavelength response than that obtained from high‐coercivity cobalt‐modified iron oxide media. The overwrite modulation of these media, however, is only marginally acceptable. The modulation noise observed is much larger for longitudinally oriented than for perpendicularly oriented media. A simple model is proposed to explain the origin...

Long-wavelength HgCdTe photodiodes operating at 20 K have been developed with quantum efficiencies >40%, bandwidths >500 MHz and a calculated heterodyne NEP = 6 × 10−20 W/Hz for a local oscillator power of 100 μW at 28 μm. A theoretical analysis along with wavelength response, pulse response and noise data are described.

Note: Conference Digest of Sixteenth Int. Conference on Infrared and Millimeter Waves, Lausanne, Switzerland, August 1991, SPIE Vol. 1576, 94 - 95 (1991) Reference CRPP-CONF-1991-016 Record created on 2008-05-13, modified on 2017-05-12