Response to illumination

A collection width of 1 jim would give a poor device for visible light sensing, if made from crystalline silicon. There is complete absorption of light in such a thin device only above about 3 eV because of the indirect band gap of the crystal. The amorphous material, however, has a higher absorption coefficient because of the relaxation of the momentum selection rules, and a 1 pm thick device absorbs light across most of the visible spectrum. 

The spectral dependence of the charge collection, Q(X), of a photovoltaic p-i-n device is shown in Fig. 10.4. The collection efficiency peaks at about 80-90 % at wavelengths between 5000-6000 A, demonstrating that there is little loss due to recombination. The 

The diffusion of carriers in the imdoped layer against the internal field also reduces the collection efficiency. A thermalized carrier can, on average, diffuse over a potential of kT. Backward diffusion can therefore occur over a distance, Xj, of approximately 

A figure of merit of the sensors is the ratio of the deep trapping or recombination time, t, to the transit time, T,  

A large ratio results in negligible carrier trapping. The value of px for electrons in good quality a-Si H is at least 10 cm V , so that a device of thickness 1 pm has no significant recombination with an internal voltage as low as 0.1 V. Even a 50 pm device has little recombination above 250 V. In practice, any bias which is sufficient to deplete the film completely is also enough to suppress recombination. 

---

Photochromic FRET using as acceptors the photochromic compounds such as spiropyrans [36]. They have the ability to undergo a reversible transformation between two different structural forms in response to illumination at appropriate wavelengths. These forms may have different absorption (and in some cases,... 

Wheeler TG, Benolken RM. Visual membranes specificity of fatty acid precursors of the electrical response to illumination. Science 1975 188(4195) 1312—1314. 

Fig. 30. Transient photocurrent response to illumination step measured at low light intensity for n-Si in 1.0 M NH4F at pH 4.5 [49]. The slow rise and fall are attributed to the slowest step in the photocurrent multiplication scheme. The semilogarithmic plot can be used to derive the value of k. Compare with Fig. 29 which demonstrates the superior resolution of IMPS.

To determine the conductivity type, note the direction of potential shift with illumination. If OCP moves Positive (towards more anodic potentials) with illumination, the material is p-type. If OCP moves Negative (towards more cathodic potentials), the material is n-type. If the potential did not change with illumination, there may be an issue with electrode fabrication/contacts, the material may be photo-inactive under these conditions, or the material may not be viable for PEC applications. If no response to illumination is observed, it is doubtfiil that the material, as mounted, wiU respond to any other photoelectrochemical characterization techniques. However, the researcher may still wish to perform CV scans as described in section Three-Electrode j-V and Photocurrent Onset to completely rule out photoactivity of the material. 

TRL Report PPR143 Driver behaviour in response to illuminated road studs a simulator study, 2006... 

In summary C. crispus and P. lanosa show similar alterations of fatty acid metabolism in response to Illumination and temperature changes as do higher plants and other algae. The acyl lipids, particularly of C. crispus, also show changes in their metabolism but not always in the same way as has been observed in higher plants. It is unclear from this work... 

Finally, the response to illumination of the prolamellar body-like structure present in the dark-grown cells is extremely sluggish a fact which... 

The response to illumination is quite rapid. Differences in specific radioactivity of RNA between illuminated and unilluminated leaves can be detected after just 15 minutes or less of illumination. 

Thus, well before massive greening begins to occur (the etiolated plants we have used generally have a lag phase ranging from 2 to 3 hours), the rate of RNA synthesis has increased in response to illumination. These observations led to an investigation of the RNA polymerase of chloroplasts and the level of its activity in illuminated and unilluminated maize leaves. 

PPR143, Driver Behaviour in Response to Illuminated Road Studs A Simulator... 

---