Switching, electronic current-voltage characteristics

A photoconductive device can function as a current switch. However, this requires a low on-resistance. For aUoyed contact devices, the current-voltage characteristics are linear at low voltage, and the current tends to saturate atincreased voltage. The current saturation is believed to be causedby electrons transferred from a high-mobility valley to a low-mobility valley, especially at the contact region where the electric field is relatively strong. 

A cost effective experimental setup for optical modulettion experiments, recently built in our laboratory. Is shown in Fig. 8 (57). Similar setup was recently reported by Tian et al. (58). Experiments performed with this system include photoreflectance (PR), electrolyte electroreflectance (EER), surface photovoltage spectroscopy (SPV), 1st. and 2nd. harmonics photoinduced current-voltage characteristics, spectral response and d.c. current-voltage characteristics. One can switch electronically between experiments and perform any number of techniques without moving the cell or removing the electrode from the electrolyte. A variable neutral... 

As the second step, the STM tip was locked over the desired particle, feedback was temporally switched off, and voltage-current (V-I) characteristics were measured. The typical trend of the V-I characteristics is shown in Figure 29. Current steps are clearly observable in the presented curve, indicating that the single-electron junction was formed. It is worth mentioning that the characteristics observed in areas without particles demonstrate a normal tunneling behavior (see Fig. 30). 

The structural information of the ARRs has been captured in an all-mode FSM. With the sensors used, all faults can be detected but cannot be isolated by analysing ARRs. It depends on how a system to be considered is built up whether further sensors can be added so that voltages across switches and currents through them can be measured. For instance, if there is a fault in one leg of the three-phase inverter or the rectifier, it can be due to a fault in one of the two switches in that leg. As to open circuit faults in switching cells, characteristic trajectories can be obtained after application of the dq-transformation that allow to isolate open switch faults. This technique not based on ARRs but often used in power electronics has been illustrated in Sect. 8.2.4 for an open circuit fault in the lower switch Sw4 of inverter leg a . 

The reason for the near identity of the ON voltage in threshold and memory switches is not yet understood as there is no coherent quantitative description of the conductive state at present. One observes that Vj is practically independent of (i) temperature, (ii) electrode separation for 0.4 < d < 5 jLtm, and (iii) electrode area. We conclude from the second point that the potential drop Vj occurs predominantly near one or both electrodes. The third point tells us that the current flow is not uniform over the contact area but instead is restricted to a region whose diameter is independent of the area as predicted by Ridley (1963) for characteristics of the type shown in Figure 6.1 (a-d). Electron microscopic evidence presented below shows that the conducting region in memory switches has a diameter of about 2 jum. 

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