The Tail States as Sensitizing Recombination Centers for Holes Lifetime in a-Si:H

1998 ◽  
Vol 507 ◽  
Author(s):  
Y. Lubianiker ◽  
R. Rapaport ◽  
I. Balberg ◽  
L. Fonseca ◽  
S.Z. Weisz
Keyword(s):  
Light Intensity ◽  
Thermal Quenching ◽  
Charge Carriers ◽  
Numerical Calculations ◽  
Dangling Bonds ◽  
Intensity Dependence ◽  
Recombination Model ◽  
Light Intensities ◽  
Recombination Centers

ABSTRACTWe have measured the dependence of the holes mobility-lifetime product on temperature under various light intensities in intrinsic a-Si:H. We find that this product exhibits thermal quenching which is accompanied by a superlinear light intensity dependence. Numerical calculations that we have carried out show that these results can be accounted for within the framework of the conventional recombination model. However, to yield such an agreement the capture coefficients for both charge carriers at the tail states must be smaller than the corresponding coefficients for the dangling bonds. Thus the sensitizing nature of the tail states is revealed.

Phototransport Properties of a-SiC:H Alloys

1995 ◽  
Vol 377 ◽  
Author(s):  
G. Nery ◽  
A. Ramirez ◽  
O. Resto ◽  
S. Z. Weisz ◽  
Y. Lubianiker ◽  
...  
Keyword(s):  
Light Intensity ◽  
Carbon Concentration ◽  
Charge Carriers ◽  
Recombination Center ◽  
Dangling Bonds

ABSTRACTWe report a study of the mobility-lifetime products of the two charge carriers in a-SiC:H alloys. The measurements were carried out as a function of the carbon concentration and the temperature. An analysis, relying on the interpretation of the corresponding light intensity exponents, indicates that neutral dangling bonds control the electrons' lifetime while another recombination center controls the holes' lifetime.

Light-Intensity Dependence of the Staebler-Wronski Effect in a-Si:H with Various Densities of Defects

2005 ◽  
Vol 862 ◽  
Author(s):  
Minoru Kumeda ◽  
Ryohei Sakai ◽  
Akiharu Morimoto ◽  
Tatsuo Shimizu
Keyword(s):  
Light Intensity ◽  
Weak Dependence ◽  
Rate Equations ◽  
Dangling Bonds ◽  
Illumination Time ◽  
Intensity Dependence ◽  
Weak Light ◽  
Staebler Wronski Effect

AbstractThe light-intensity dependence of the photocreation of dangling bonds (DBs) were investigated for a-Si:H films with increasing density of defects before light soaking. Samples in which the density of neutral DBs had been increased by annealing at 400 C for 1 h exhibited a weak light-intensity dependence of the photocreated DBs compared to that for the as-deposited sample. Furthermore, the sample which had been illuminated with a light intensity of 1 W/cm2 for 1 h also showed a weak dependence. The results can be qualitatively explained by using rate equations for the densities of DBs and floating bonds (FBs) based on the FB-mediated photocreation of DBs. When both the densities of DBs and FBs before illumination increase, the light-intensity dependence of the DB density for a moderate value of the illumination time becomes weaker, qualitatively consistent with the observed results.

Thermal Quenching of Photoconductivity and the Sign of Photocarriers in Doped a-Si:H

1991 ◽  
Vol 219 ◽  
Author(s):  
B.-G. Yoon ◽  
H. Fritzsche ◽  
M. Q. Tran ◽  
D.-Z. Chi
Keyword(s):  
Light Intensity ◽  
Cross Section ◽  
Capture Cross Section ◽  
Thermal Quenching ◽  
Capture Cross ◽  
Present Evidence ◽  
Normal Cross Section ◽  
Recombination Centers ◽  
P Type ◽  
Minority Carriers

ABSTRACTThermal quenching (TQ) of photoconductivity σp occurs when the demarkation level of minority carriers passes through recombination centers having small capture cross section for majority carriers compared to other centers present but normal cross section for minority carriers. The photoconductivity becomes superlinear with light intensity at the temperature of maximum TQ. We discovered TQ not only in n-type but also p-type a-Si:H. This cannot happen with the same centers unless the sign of the majority carriers changes. We present evidence that in p-type and undoped films majority carriers are electrons at T below TQ and holes above TQ. The nature of these special centers will be discussed.

Mobility-Lifetime Products in Glow Discharge and RF Sputter Deposited A-Si:H

1994 ◽  
Vol 336 ◽  
Author(s):  
M. H. Farias ◽  
A. Roche ◽  
S. Z. Weisz ◽  
H. Jia ◽  
J. Shinar ◽  
...  
Keyword(s):  
Light Intensity ◽  
Glow Discharge ◽  
Comparative Study ◽  
Deposition Temperature ◽  
Charge Carriers ◽  
Dangling Bonds ◽  
Majority Carrier ◽  
Recombination Processes ◽  
Pool Model ◽  
Sputter Deposited

ABSTRACTA comparative study of the deposition temperature (Ts) dependence of the Mobility-lifetime (μτ) products of the charge carriers in glow-discharge and rf sputter-deposited a-Si:H is described and discussed. The Ts-dependence of the μτ's the majority carrier light-intensity exponents of the two types of films are strikingly similar. These observations lead to the conclusion that the structure of the recombination levels as well as the recombination processes are in accord with the “defect pool” Model, in contrast to previous suggestions. The differences between the two types of films thus appear to be limited to the differences in the concentrations of dangling bonds.

scholarly journals Effect of chlorophyll biosynthesis-related genes on the leaf color in Hosta (Hosta plantaginea Aschers) and tobacco (Nicotiana tabacum L.)

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Jingying Zhang ◽  
Changhai Sui ◽  
Huimin Liu ◽  
Jinjiao Chen ◽  
Zhilin Han ◽  
...  
Keyword(s):  
Light Intensity ◽  
Antioxidant Capacity ◽  
Aminolevulinic Acid ◽  
Chlorophyll Biosynthesis ◽  
Expression Level ◽  
Virus Induced Gene Silencing ◽  
Leaf Color ◽  
Color Changes ◽  
Light Intensities ◽  
Structure Changes

Abstract Background ‘Regal Splendour’ (Hosta variety) is famous for its multi-color leaves, which are useful resources for exploring chloroplast development and color changes. The expressions of chlorophyll biosynthesis-related genes (HrHEMA, HrPOR and HrCAO) in Hosta have been demonstrated to be associated with leaf color. Herein, we isolated, sequenced, and analyzed HrHEMA, HrPOR and HrCAO genes. Subcellular localization was also performed to determine the location of the corresponding enzymes. After plasmid construction, virus-induced gene silencing (VIGS) was carried out to reduce the expressions of those genes. In addition, HrHEMA-, HrPOR- and HrCAO-overexpressing tobacco plants were made to verify the genes function. Changes of transgenic tobacco were recorded under 2000 lx, 6000 lx and 10,000 lx light intensity. Additionally, the contents of enzyme 5-aminolevulinic acid (5-ALA), porphobilinogen (PBG), chlorophyll a and b (Chla and Chlb), carotenoid (Cxc), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), proline (Pro) and catalase (CAT) under different light intensities were evaluated. Results The silencing of HrHEMA, HrPOR and HrCAO genes can induce leaf yellowing and chloroplast structure changes in Hosta. Specifically, leaves of Hosta with HrCAO silencing were the most affected, while those with HrPOR silencing were the least affected. Moreover, all three genes in tobacco were highly expressed, whereas no expression was detected in wild-type (WT). However, the sensitivities of the three genes to different light intensities were different. The highest expression level of HrHEMA and HrPOR was detected under 10,000 lx of illumination, while HrCAO showed the highest expression level under 6000 lx. Lastly, the 5-ALA, Chla, Cxc, SOD, POD, MDA, Pro and CAT contents in different transgenic tobaccos changed significantly under different light intensities. Conclusion The overexpression of these three genes in tobacco enhanced photosynthesis by accumulating chlorophyll content, but the influential level varied under different light intensities. Furthermore, HrHEMA-, HrPOR- and HrCAO- overexpressing in tobacco can enhance the antioxidant capacity of plants to cope with stress under higher light intensity. However, under lower light intensity, the antioxidant capacity was declined in HrHEMA-, HrPOR- and HrCAO- overexpressing tobaccos.

A laboratory study of vertical migration

1955 ◽  
Vol 144 (916) ◽  
pp. 329-354 ◽  
Keyword(s):  
Light Intensity ◽  
Vertical Migration ◽  
Time Course ◽  
Tap Water ◽  
Low Light ◽  
Overhead Light ◽  
Light Intensities ◽  
Orientation Response ◽  
Reduced Light ◽  
Characteristic Maximum

In a tank filled with a suspension of indian ink in tap water, a population of Daphnia magna will undergo a complete cycle of vertical migration when an overhead light source is cycli­cally varied in intensity. A ‘dawn rise’ to the surface at low intensity is followed by the descent of the animals to a characteristic maximum depth. The animals rise to the surface again as the light decreases, and finally show a typical midnight sinking. The light intensities at the level of the animals in this experiment are of the same order as those which have been reported in field observations; the time course of the movement also repeats the natural conditions in the field. The process is independent of the duration of the cycle and is related only to the variation in overhead light intensity. At low light intensity the movement of the animal is determined solely by positive photo-kinesis; the dawn rise is a manifestation of this, and is independent of the direction of the light. At high light intensities there is an orientation response which is superimposed upon an alternating positive (photokinetic) phase and a negative phase during which movement is inhibited. The fully oriented animal shows a special type of positive and negative phototaxis, moving towards the light at reduced light intensities and away from it when the light intensity is increased. In this condition it follows a zone of optimum light intensity with some exactness. Experiments show that an animal in this fully oriented condition will respond to the slow changes of intensity characteristic of the diurnal cycle, while being little affected by tran­sient changes of considerable magnitude.

Two Carrier Sensitization as a Spectroscopic Tool for a-Si:H

1999 ◽  
Vol 557 ◽  
Author(s):  
L.F. Fonseca ◽  
S.Z. Weisz ◽  
R. Rapaport ◽  
I. Balberg
Keyword(s):  
Carrier Lifetime ◽  
Minority Carrier ◽  
Thermal Quenching ◽  
Minority Carrier Lifetime ◽  
Dangling Bond ◽  
Recent Letter ◽  
Recombination Centers ◽  
Spectroscopic Tool ◽  
Hydrogenated Amorphous ◽  
Effect Of Light

AbstractIn a recent letter we have reported the first observation of the phenomenon of minority carrier-lifetime sensitization in hydrogenated amorphous silicon (a-Si:H). We find now that combining the study of this phenomenon with the study of the well-known phenomenon of majority carrier lifetime sensitization, in this material, can provide direct information on its density of states (DOS) distribution. This finding is important in view of the limitations associated with other methods designed for the same purpose. We have carried out then an experimental study of the effect of light soaking on the phototransport in a-Si:H. We found that the increase of the dangling bond concentration with light soaking affects the sensitization and thermal quenching of the majority carriers lifetime. Using computer simulations, we further show that the details of the observations associated with the sensitization effect yield semiquantitative information on the concentration and character of the recombination centers in a-Si:H.

Pycnidium production by Botryodiplodia theobromae. I. The relation of light to the induction of pycnidia

1969 ◽  
Vol 47 (7) ◽  
pp. 1153-1156 ◽  
Author(s):  
J. A. Ekundayo ◽  
R. H. Haskins
Keyword(s):  
Light Intensity ◽  
Ultraviolet Radiation ◽  
Exposure Period ◽  
Fluorescent Light ◽  
Botryodiplodia Theobromae ◽  
Continuous Irradiation ◽  
Long Wave ◽  
Light Intensities ◽  
Glass Color ◽  
Color Filters

Cultures of Botryodiplodia theobromae Pat. produced pycnidia abundantly on several media under continuous irradiation with fluorescent light. The fungus did not sporulate when grown in darkness. Irradiation of cultures with a light intensity of 15 foot-candles for 4 days was sufficient to stimulate pycnidial production, but for appreciable sporulation to occur over the same exposure period, higher light intensities are required. Irradiation of cultures through glass color filters showed that long-wave ultraviolet radiation stimulated sporulation.

Light-Intensity Dependence In The Kinetics Of N-Gap Photoelectrode Stabilization

2010 ◽  
Vol 89 (3) ◽  
pp. 181-186 ◽  
Author(s):  
F. van Overmeire ◽  
F. Vanden Kerchove ◽  
W. P. Gomes ◽  
F. Cardon
Keyword(s):  
Light Intensity ◽  
Intensity Dependence ◽  
Kinetics Of
Sign in / Sign up

Export Citation Format

Share Document