Ultrafast diodes

Figure 3-29 Forward conduction voltage characteristic of the Schottky versus the ultrafast diode.

Note that input bridge packs using ultrafast diodes are often peddled as offering... 

Input bridges that use ultrafast diodes are available, and their vendors claim significant reduction in EMI. But in practice they don t seem to provide much advantage. They also typically have much lower input surge current ratings. In fact... 

Virgili T, Cerullo G, Luer L, Lanzani G, Gadermaier C, Bradley DDC (2003) Understanding fundamental processes in poly(9,9-dioctylfluorene) light-emitting diodes via ultrafast electric-field-assisted pump-probe spectroscopy. Phys Rev Lett 90(24) 247402... 

The first realization of a conjugated polymer/fullerene diode [89] was achieved only recently after the detection of the ultrafast photoinduced electron transfer for an ITO/MEH-PPV/Ceo/Au system. The device is shown in Figure 15-18. Figure 15-19 shows the current-voltage characteristics of such a bilayer in the dark at room temperature. The devices discussed in the following section typically had a thickness of 100 nm for the MEH-PPV as well as the fullerene layer. Positive bias is defined as positive voltage applied to the ITO contact. The exponential current tum-on at 0.5 V in forward bias is clearly observable. The rectification ratio at 2 V is approximately 10". ... 

As shown above, the short circuit current, reaches 0.5 mA/cm under 20 mW/ cm illumination, corresponding to a collection efficiency of rjc = lA% electrons per incident photon. This value is approximately two orders of magnitude higher than that of pure MEH-PPV tunnel diodes as well as of the non-optimized MEH-PPV/Ceo heterojunction device as described in the previous section. The electroluminescence quantum efficiency of this blend device was 10 —10 times less than in pure MEH-PPV devices, consistent with the ultrafast photoinduced charge separation, which quenches the emission of the donor. The efficiencies are nearly independent of the incident illumination intensity as shown in Figure 15-28. Furthermore, the internal efficiencies are even higher when corrected for the small thickness of the film, which absorbs only 60% of the incident photons. 

The pulse-probe technique can be extended to multiwavelength detection by using the ultrafast laser pulse to generate a white-light continuum probe, which can be dispersed with a spectrograph across a diode array or CCD detector after traversing the sample. Due to lower probe intensity, Cerenkov emission from the sample would be expected to be more of a complication in this case, but the correction methods developed for stroboscopic Cerenkov detection would also work here. 

Dang, F, Zhang, F., Hagiwara, H., Mishina, Y. and Baba, Y. Ultrafast analysis of oligosaccharides on microchip with light-emitting diode confocal fluorescence detection. Electrophoresis, 24, 714, 2003. 

Acousto-Optics Lasers Lasers, Semiconductor Lasers, Ultrafast Pulse Technology Light Emitting Diodes... 

For measurements of optical frequencies, ultrafast metal-insulator-metal (MIM) diodes have been developed [4.110], which can be operated up to 66THz (k = 3.39 xm). In these diodes, a 25-fim diameter tungsten wire, elec-trochemically etched to a point less than 200 nm in radius, serves as the point contact element, while the optically polished end of a nickel plate with a thin oxide layer forms the base element of the diode (Fig. 4.89). 

Ultrafast Schottky barrier diodes and metal oxide semiconductor field-effect transistors (MOSFETs)... 

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