P-n junction diodes

Fig. 7. Circuit symbol and current, /, voltage, U, characteristic of a p—n junction diode where = breakdown voltage(32).

The p-n junction diodes employing catalytic metal contacts have recently been tested for their gas-sensing properties [66, 67]. The catalytic metal contact was placed directly on the semiconductor in this device, as shown in Figure 2.6. In general the response appears to be lower than for the traditionally used devices described earlier in this section. However, this means that for any catalytic metal used as an ohmic contact to a p-n junction, it can be expected that the /-Vcharacteristics will be influenced, for example, in a hydrogen-containing atmosphere. 

Figure 6 Schematic diagram of the double-heterostructure p-n junction diode used for chemical sensing experiments. Electrical contact is made to the top and bottom surfaces with metal films. (Adapted from Ref. 3.)...

Photovoltaic Cells Used us a tunnelling (aver in an MIS solar cell or as an active laser in p-n junction diode, perhaps involving an inorgan ic/organic junction. 

A simplified example will illustrate the process of microstructure fabrication. With reference to Fig. 1, an //-type region has been created by diffusion of a donor impurity into a surface of p-type silicon, forming a p — n junction diode. There is a metal contact to the /(-region, and the contact line is insulated from the p-type surface by a layer of silicon dioxide. The diameter of the diode is on the order of 10 micrometers. 

An interesting variant on this theme is the polypyrrole-polythiophene p-n junction diode, prepared by forming the two anion-doped polymers sequentially and then redoping the thiophene layer with cations. At 10 V the diode had a forward current of 15 mA and a current of 1 mA in reverse bias3l6). 

A reverse voltage is applied to a silicon p-n junction diode to make a thick depletion layer. Most of the light is absorbed in the depletion layer. The resulting electrons and holes are separated and caused to drift in the electric field within the depletion layer, producing a photocurrent. 

Semiconductor p-n junction diode thermometers (Swartz and Gaines, 1972 Verster, 1972 Ohteetal., 1982) are becoming widely used throughout the range from liquid helium temperatures (1 K) to about 200°C. The diodes are currently made of germanium, silicon, or gallium arsenide. These thermometers are based on the principle that for forward-biased... 

Schottky barrier diodes - a diode consisting of a metal-semiconductor contact which has rectifying characteristics similar to a p-n junction differs from a p-n junction diode in that the diode s forward voltage is different (lower for commonly used materials), and there is no charge stored when the diode is forward biased device can therefore be turned off very rapidly by application of reverse bias, as storage time is negligible. 

Suzuki and co-workers [14,15] fabricated P-SiC p-n junction diodes using a mesa structure. The tum-on voltage at room temperature was 1.2 V and a reverse leakage current of 5 pA was measured at - 5 V. This leakage current is much greater than that for a-SiC diodes. Both parameters were severely degraded at elevated temperatures. Edmond et al [16] and Avila et al [17] have also produced p-n junction diodes in P-SiC. These diodes were made by ion implantation and operated up to 673 K. 

The electrical behaviour that emerges when a region of p-type semiconductor is adjacent to a region of n-type semiconductor, a p-n junction diode, often just... 

From what has been said, it can be seen that a p-n junction diode acts as a rectifier. That is, the device... 

---