High Illumination Conditions Research Articles

Mechanism of impact ionization enhancement in GaAs p-i-n diodes under high illumination conditions

Recent experimental work on AlGaAs p-i-n photodiodes [Dudley R A and Vickers A J 1995 Proc. Hot Carriers in Semiconductors IX (New York: Plenum)] has generated evidence that the transient photocurrent produced by high-intensity pulsed laser illumination is larger than expected for any given value of the bias. It has been postulated that this enhancement is due to the modification of the internal electric field by the photogenerated charge. A similar effect has been seen in calculations for metal-semiconductor-metal semiconductors [Dunn G M, Rees G J and David J P R 1997 Semicond. Sci. Technol. 12 692-7], but we present here details of the first calculation of the effect in a p-i-n diode. A drift-diffusion model is used to calculate photocurrent versus reverse bias for several values of illumination intensity, illustrating the enhancement effect. The origin of the enhancement is then highlighted and explained.

Quantal processing of visual information in the brain

In order to test if vision is a continuous processing system that analyses information immediately after it arrives at the retina or a discontinuous system that accumulates information and periodically analyses a data quantum, the time required by 38 healthy adults to solve simple visual tasks was accurately quantified. The main finding of the present study was that the processing time for visual tasks is always a multiple of a basic unit whose duration was 30–40 ms. Present data support the hypothesis that visual information is processed in the brain with a discontinuous flow of discrete-time quanta. Data suggest two processing ways for the visual system, one that with a high time-resolution (30–40 ms) operates under high-illumination conditions, and the other that with a low time-resolution (100–120 ms) is put into operation in low-illumination conditions.

Stabilized Three Color Piinip Sensor For High Illumination Conditions

ABSTRACTA stabilized three color piinip sensor for high illumination conditions was developed. The spectral response of the novel device shows a maximum at 480nm, 530nm and 630nm changing the applied bias voltage from −0·2V, −2·OV to 2·OV, respectively. Only a slight influence on the device performances is observed after more than 100h light soaking under AM1·5 illumination conditions. This is achieved by employing low temperature deposited a-Si:H with high hydrogen dilution and a microcrystalline silicon layer in the top diode of the sensor. For piinip detector systems with different absorption materials in the top diode the influence of light induced degradation on the spectral response and the dark current is discussed. Furthermore, the transient behavior of the new stabilized detector is presented.

Resonant inelastic light scattering by electronic excitations in tunable quantum wire structures

Resonant inelastic light scattering was used to investigate both charge density excitations and spin density excitations in shallow etched GaAsAl/GaAs quantum wires. A semi-transparent Schottky gate was evaporated on top of the samples which allowed a strong tunability of the electron density and the lateral confinement, even under high illumination conditions used for inelastic light scattering. The range of charge density excitations extended from confined plasmons to a plasmon band structure. Both intra- and intersubband single-particle excitations were observed. The occurrence of a tunable doublet structure in depolarized plane wave spectra is attributed to spin flip intrasubband single-particle excitations.

Relative effects of turbidity and light intensity on reactive distance and feeding of an estuarine fish

Gulf killifish Fundulus grandis were allowed to prey on daggerblade grass shrimp Palaemonetes pugio in clear water with bright light, turbid water containing bentonite clay, and clear water treatments where the light intensity was adjusted to match that in the bottom of the turbid tanks. Significantly fewer shrimp were consumed in the turbid tanks relative to the clear and shade treatments where predation rates did not differ significantly. The results suggested that the influence of suspended particles on predation rates was a consequence of light scattering and was not related to a decrease in light intensity. Reactive distances were subsequently determined for human observers viewing a small target in elongated tanks containing turbid water (7.3–60.5 NTU) under conditions of both low (8-10 μE m−2 s−1) and high illumination (153–1249 μE M−2 s−1). Reactive distance was primarily governed by turbidity while light intensity had little influence except at low turbidities. The shape of the relationship between reactive distance and turbidity for humans resembled curves reported for a variety of fish species.

High optical power nonlinear dynamic response of AlInAs/GaInAs MSM photodiode

In this paper, we introduce a theoretical study and a numerical simulation of the nonlinear electrical response, including the harmonic-generation rate calculation, of an MSM AlInAs/GaInAs photodiode under high-illumination conditions. We also report that, with an MSM operating at 20 GHz, we can expect a saturation limit at a maximum modulated optical power as high as 100 mW. >

Inoculum Density-Dependent Mortality and Colonization of the Phyllosphere by Pseudomonas syringae

Pseudomonas syringae inocula containing cell concentrations ranging from 10 to 10 cells per ml were applied to the primary leaves of bean plants. The plants were incubated under conditions of high temperature and illumination and low relative humidity. Bacterial mortality rates and the proportional population decline of the inoculum were lowest at the highest inoculum concentrations. Addition of a high concentration of heat-killed cells to the inoculum containing a low concentration of viable cells significantly reduced both the mortality rate and the proportional population decline of the viable cells. The mechanisms underlying this density-dependent mortality may include cooperative protective effects of extracellular factors, such as bacterial extracellular polysaccharides, and physical protection by neighboring cells. Although epiphytic populations derived from inoculum concentrations of 10 or 10 cells per ml tended toward 10 CFU/g, the presumed carrying capacity of the leaf, populations derived from lower inoculum concentrations never achieved this carrying capacity. Assuming that epiphytic populations of P. syringae reside in discrete protected sites, our results suggest that at low inoculum concentrations, following a period of environmental stress, the number of viable cells may have dropped to zero in some sites; hence, the carrying capacity of the leaf could not be achieved.

Relationship between Diurnal Activity Patterns, Cryptic Coloration, and Subsequent Avoidance of Predaceous Fish by Perlid Stoneflies

We demonstrate that prey (stoneflies), which are either solidly coloured or patterned, coordinate intervals of maximum daytime activity with periods when visually foraging predators (rainbow trout, Oncorhynchus mykiss) are least able to detect them. In this study, rainbow trout attacked solidly coloured stonefly nymphs (Paragnetina media) more frequently under conditions of low illumination (simulated dawn and dusk) than high illumination (simulated midday) whereas the frequency of attacks on patterned stonefly nymphs (Agnetina capitata) was reversed. Consequently, in both the presence and absence of trout, the activity (i.e. frequency of crawling) of P. media and A. capitata was highest under conditions of high and low illumination, respectively. The number of attacks by trout on all nymphs was significantly less when nymphs were on dark-brown, rather than mottled, substrates. When given a choice between dark-brown and mottled substrate, both species selected dark substrate. Suggestions that the visual acuity of predators varies as a function of light intensity and the coloration, patterning, and daytime activity of prey are corroborated for the first time.

The role of the emitter on the diffusion current inn + p-junctions

On three different samples of crystallinep-siliconn+p-junctions have been prepared by coating the surface with a phosphorous glass and a subsequent diffusion at 915°C for 30 min. From the measurement of the short circuit current density and the open circuit voltage under high illumination conditions the diffusion current of the solar cells has been determined as a function of the temperature between 77K and 300 K. The contribution of the emitter and the base region to the diffusion current was examined. Under the assumption of Auger recombination governing the hole lifetime in the emitter the narrowing of the mobility bandgap due to the high density of states within the bandgap of the emitter was determined. A shrinkage as high as 0.18 eV was observed in the case of a 0.2 μcm sample of lower purity. For high purity 6 μcm silicon the reduction of the mobility bandgap was determined as 0.10 eV. A polycrystalline sample exhibits a shrinkage of 0.15 eV. The reduction of the mobility bandgap was found to determine the lower limit of the current losses due to carrier diffusion in our solar cells at current densities around 1×10−7 Am−2.

Numerical simulation of the nonlinear response of a p-i-n photodiode under high illumination

A theoretical study and a model for the numerical simulation of the nonlinear electrical response, including the harmonic-generation rate calculation, of a p-i-n InGaAs photodiode under high-illumination conditions are discussed. The device structure is described. An algorithm, which is based on a finite-difference calculation, is used to calculate the temporal electrical response of the device to a microwave optical input signal. The different harmonics in the power spectrum are obtained using the fast Fourier transform (FFT) calculation. This model is a tool for designing the p-i-n photodiode and determining the conditions for its utilization in order to avoid the electrical response nonlinearity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of the diode ideality factor on the experimental determination of series resistance of solar cells

Two experimental methods of determining the lumped series resistance of silicon solar cells are investigated. Both methods are based on the solution of the basic solar cell equation in conjunction with actual data taken from a single current-voltage ( I–V) output curve. The assumption of a constant diode ideality factor along the entire I–V output characteristic is common in the derivation of both methods. It is shown that this assumption is inaccurate at normal intensities and can lead to erroneous results. It is evident that both methods are useful over only a limited range of solar cell operation and are accurate only for cells operating under very high illumination conditions where it is appropriate to assume that the diode ideality factor is constant at unity along the entire I–V curve.

Comments on the experimental determination of series resistance in solar cells

A method for measuring the series resistance of a solar cell recently proposed by Araujo and Sanchez [1] is compared with that proposed by Wolf and Rauschenbach [2]. It is shown that the former method is accurate only for cells with very low R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> and operating under high illumination conditions. The latter method is able to determine R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> at any particular operating point of the I-V characteristic without a prior knowledge of the other parameters, provided these parameters are independent of illumination.

Analysis of the facilitatory effect of the ACTH-(4–9) analog ORG 2766 on active social contact in rats

Pairs of male rats were tested for active social interaction, either in a familiar test arena under low illumination or in an unfamiliar test arena under high illumination conditions. Rats tested in an unfamiliar environment and under high light, spent less time in active social contact than rats tested under familiar, low light conditions. This effect was not pronounced during the first half of the 10 minute test period. Intraperitoneal injections of ACTH-(1–24) and ACTH-(4–10) (50 μg/kg) administered 5 minutes before the test decreased, whereas the same dose of the synthetic ACTH-(4–9) analog ORG 2766 increased the time spent in active social contact, when rats were tested under unfamiliar, high light conditions. The effects of ACTH-(4–10) and ORG 2766 were present in the second and first half of the test period respectively. Dose response relationship studies with ORG 2766 showed that 0.5 μg/kg of this peptide facilitated social contact under both test conditions and the dose response relation followed an inverted U-shaped curve under the familiar low light condition, but not under the unfamiliar, high light condition. ACTH-(4–10) and ORG 2766 failed to influence active social contact, when administered 30 minutes before the test. The change in social contact by ACTH-(4–10) and ORG 2766 was not accompanied by an alteration in ambulation of the rats. It is concluded that ACTH-(4–10) and ORG 2766 decrease and increase respectively social interaction of pairs of rats. The expression of these effects however, depends on the test and treatment conditions and may be related to the action of brain-born ACTH-like peptides.

Time estimation in humans: effects of ambient illumination and sex.

7 male and 7 female college students made estimations of 15-sec. intervals in conditions of dark, low and high ambient illumination. Analysis of variance showed significant effects of illumination and illumination by sex. Increased light levels shortened time estimation except for males under high light intensity. Results are discussed in terms of arousal theory and the relevance of these factors in research on time estimation.

Gas-exchange studies with the staghorn coral Acropora acuminata and its zooxanthellae

Compensation point and light-saturation values were determined from oxygen-exchange experiments with branches and isolated zooxanthellae from the staghorn coral Acropora acuminata. Branches and dense suspensions of zooxanthellae showed similar lightresponse curves for oxygen exchange, with light saturation at about 23 Klux (300 W. m-2) and compensation point occurring between 4 and 6 Klux (60–80 W. m-2). Zooxanthellae appear to be mutually shaded in dense suspensions and coral tissues. The effects of metabolic inhibitors, including photosynthetic and respiratory inhibitiors, on oxygen exchange in coral branches and isolated zooxanthellae are presented. Bubbles formed on coral tissues and on several macroalgae under conditions of high illumination contained large amounts of oxygen, suggesting that a high oxygen tension may occur in coral tissues during the day. Photorespiration and dissolved organic carbon production by suspensions of zooxanthellae are discussed in relation to a high oxygen tension which probably occurs in coral tissues during daylight.

Release of Glycollate from Tropical Marine Plants

Release of glycollate under conditions of high illumination and high oxygen concentration from tropical seaweeds representing the groups Chlorophyta, Phaeophyta and Rhodophyta, and from two marine angiosperms, has been demonstrated. The amount released is increased by the presence of alumina as an adsorbent. Quantitative determination is rendered difficult by the simultaneous release of a substance(s), also adsorbed on alumina, which interferes in the colorimetric analysis for glycollate. The concentration of glycollate in surface water in the Coral Sea was determined on two occasions as 0.015 mg I-1.

Stimulus Familiarity and Alley Illumination as Determinants of Approach Response Latencies of House Crickets

To examine the effects of stimulus familiarity on the odor preferences of insects, crickets were lodged in bins permeated with either cherry extract or oil of camphor. After approximately 3 and 9 days of such exposure, Ss were placed in an alley in which a rag doused with either the familiar or novel substance was present in the goal area. Half the Ss were tested under conditions of low illumination, and half under conditions of high illumination. Ss more rapidly approached the familiar stimulus, but this effect was largely due to the performance of crickets in. one of the two exposure conditions. An interaction indicated that exposure to the cherry extract increased its relative attractiveness, while exposure to the oil of camphor decreased its relative unattractiveness. Latencies were shorter under conditions of high than low illumination. A simple incentive model was used to account for the co-effects of familiarity and illumination.

The Effect of Reciprocal Cultivation in the Two Ecotypes of Vernonia patula (Dryand.) Merrill.

Two ecotypes in Vernonia patula have been observed, viz., the erect type and the prostrate decumbent type. The erect type is an annual plant found in small colonies under shady habitats but the decumbent type is a common, perennial plant of open grasslands. Soil analyses reveal that the erect type occurs in base rich neutral soil whereas the decumbent type has base poor, sandy and acidic soil. Large numbers of morphological and physiological characters, such as initiation of early inflorescence, mode and magnitude of inflorescence, dry weight per plant show wide differences which have been observed at several occasions in different populations of the either type of Vernonia patula. Four months of cultivation of the either type of Vernonia patula, under reciprocal substratum and light conditions affect intensity of phenotypic expression of the genotype yet their differences are consistent, throughout the observations. Thus it appears that the two types of Vernonia patula investigated are ecotypes. The prostrate decumbent type of Vernonia patula has adapted to encounter hard compact dry soil, exposed to high illumination and temperature conditions and heavy to mild biotic operations, on the contrary, the erect type grows in neutral and base rich soil during favourable season of the year.

Background light intensity and the pupillary response in a reaction time task

In an auditory reaction time task, changes in pupillary dilation were monitored during conditions of high and low background illumination. The latter were found to determine pupillary baseline levels, while the amplitude of the dilation peak at response stayed at a constant value. Unfulfilled expectancy that a response signal would occur was found to induce a smaller expectancy peak, despite the absence of an associated motor response. It was confirmed that temporal uncertainty relating to the length of the warning foreperiod could partly determine the Ss’ RT performance.

Judgment of size with varying conditions of stimulus duration and illumination.

40 Ss assigned stimuli consisting of square grey patches of side lengths 1 in., 1½ in., 1½ in., 1¾ in. and 2 in., into 5 categories according to perceived size. The stimuli were viewed tachistoscopically under 4 conditions of duration—625, 125, 25, and 5 msec.—and two conditions of illumination—1.00 and 0.80 log ft-L. on white. Half the Ss experienced high illumination conditions and the other half low. Pre-test training in the correct assignment of the stimulus set to the appropriate categories was given under conditions of free inspection. Data obtained from the 5-msec. treatment for both high and low illumination conditions were scaled by the graphical method of Diederich, Messick, and Tucker. The resulting scale values were interpreted as showing a constant shift in perceived size toward the smaller end of the size scale. The differences in slope and position of the graph of scale values against real size for the two illumination conditions suggest that the size shrinkage effect is a function of the interaction of illumination and duration.