Effect of temperature on the intensity and carrier lifetime of an AlGaAs based red light emitting diode

The influence of temperature on the intensity of light emitted by as well as the carrier life time r of a standard A1GaAs based light emitting diode has been investigated in the temperature range from 345 to 136 K. The open-circuit voltage decay （OCVD） technique has been used for measured the carrier lifetime. Our experimental results reveal a 16% average increase in intensity and a 163.482-19.765 ns variation in carrier lifetime in the above temperature range. Further, theoretical and experimental analysis show that for negligible carrier density the intensity is inversely proportional to carrier lifetime for this sample.

Influence of temperature on tunneling-enhanced recombination in Si based p–i–n photodiodes

We investigate the dominant dark current transport mechanism in Si based p-i-n photodiodes, namely, BPW 21R, SFH 205FA and BPX 61 photodiodes in the temperature range of 350 to 139 K. The forward current- voltage characteristics of these photodiodes are explained via the tunneling enhanced recombination model, which gives a quantitative description of the electronic mechanism in the p-i-n junction photodiodes. The observed tem- perature dependence of the saturation current and the diode ideality factor of these devices agree well with theo- retical predictions; the analysis also indicates the importance of doping for enhancement of tunneling. The present study will be helpful in applying the devices at low temperature ambience.

Effect of COOH-functionalized SWCNT addition on the electrical and photovoltaic characteristics of Malachite Green dye based photovoltaic cells

We report the effect of COOH-functionalized single walled carbon nanotubes（COOH-SWCNT） on the electrical and photovoltaic characteristics of Malachite Green（MG） dye based photovoltaic cells. Two different types of photovoltaic cells were prepared, one with MG dye and another by incorporating COOH-SWCNT with this dye. Cells were characterized through different electrical and photovoltaic measurements including photocurrent measurements with pulsed radiation. From the dark current–voltage（I–V） characteristic results, we observed a certain transition voltage（Vth/ for both the cells beyond which the conduction mechanism of the cells change sharply. For the MG dye, Vthis 3.9 V whereas for COOH-SWCNT mixed with this dye, Vthdrops to 2.7 V. The device performance improves due to the incorporation of COOH-SWCNT. The open circuit voltage and short circuit current density change from 4.2 to 97 m V and from 108 to 965 A/cm2 respectively. Observations from photocurrent measurements show that the rate of growth and decay of the photocurrent are quite faster in the presence of COOH-SWCNT. This observation indicates a faster charge separation processes due to the incorporation of COOHSWCNT in the MG dye cells. The high aspect ratio of COOH-SWCNT allows efficient conduction pathways for the generated charge carriers.

Improvement of electrical and photovoltaic properties of methyl red dye based photoelectrochemical cells in presence of single walled carbon nanotubes

In this work, we investigated the effect of single walled carbon nanotubes （SWCNT） on the electrical and photovoltaic properties of methyl red （MR） dye based photoelectrochemical cell （PEC）. MR dye based PEC with LiCl04 as ion salt were fabricated with and without mixing SWCNT. The cells were characterized through electrical and optical measurements. The performance of the devices changed drastically in presence of SWCNT. The transition voltage and trap energy of the cells were estimated from the steady-state dark current voltage （I-V） analysis. The transition voltage and trap energy decreased for MR dye cell in presence of SWCNT. Open circuit voltage （Voc）, short circuit current （Jsc）, fill factor （FF） and power conversion efficiency （v/） increased due to the addition of SWCNT. Further measurement of the transient photo- current showed that the growth and decay of photocurrent was quite faster in presence of SWCNT. The photocurrent decay with time was fitted for both the cells and found to follow a power law relation which indicates dispersive transport mechanism with exponential trap states distrib- uted in between lowest unoccupied molecular orbital （LUMO） and highest occupied molecular orbital （HOMO） levels. Possible interpretation is done on the lowering of trap energy with the photocurrent. These results suggest that SWCNT lowers the trap energy of the cells by providing efficient percolation pathways for the conduction of charges. It is expected that due to lowering of trap energy the residing time of the free carriers within the traps decreases. In other words, it may also be said that the charge recombination decreases. These factors affect the overall conduction of charges and improve the electrical and photovoltaic properties.

Funneling current in Si-doped infrared n type-GaAs heterostructures emitter

In the present work, we measured the forward bias current-voltage （I-V） characteristics of Si-doped n type gallium arsenide （GaAs） heterostructures infrared emitter over a wide temperature range from 350 to 77 K. Results showed that the slopes of the exponential curve changed slowly with temperature. The analysis of the various tunneling mechanisms indicated that the tunneling current varied approximately as a function of - exp（- αEg ＋ βeV） where the parameters α and β varied indistinctively with temperature and voltage tunneling current on the The dependence of forward temperature and bias can be explained by thermally induced band gap shrinkage and bias induced route change respectively. These results will be helpful for application of the optoelectronics device in both high and low temperature ambiences.