Semiconductor p-n junction

Fig. 2. Representation of the band edges in a semiconductor p—n junction where shallow donor, acceptor energies, and the Fermi level are labeled Ejy E, and E respectively, (a) Without external bias is the built-in potential of the p—n junction (b) under an appHed forward voltage F. ...

Fig. 8.9 Schematic diagram of PV-electrolysis systems proposed for solar water splitting (a) Electricity generated from photovoltaic cell driving water electrolysis (b) PV assisted cell with immersed semiconductor p/n junction as one electrode.

C. P. Please, An Analysis of Semiconductor p-n Junctions, D. Phil, thesis, Oxford University, Oxford, 1978. 

Here we will discuss some concrete technologies based on photovoltaic (PV) effect in solar cells. Actually PV energy systems and computer technology based on the semiconductor p-n junctions that is why energy supply systems based on PV systems are very suitable to computer systems by electrical matching. 

Figure 1 The schematic representation of various electronic excitation mechanisms due to ac or dc external electric fields (a) the tuneling electrons from the valence band (VB) to the conduction band (CB) and ionization of an acceptor state (-o-) (Zener effect) followed by electron-hole recombination, indicated by horizontal and vertical arrows, respectively (b) excitation or ionization by electron impact (c) recombination of electrons ( ) and (o) holes at a semiconductor p-n junction and (d) bulk recombination of electrons and holes injected from electrodes. Adapted from Ref. 2...

Dye-sensitized nanocrystalline cells are fundamentally different from the others discussed earlier in that they do not rely on semiconductor p-n junctions. Instead, they are electrochemical devices in which the optical absorption and carrier-collection processes are separated (Fig. 4). 

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... 

A p n junction is formed wherever a region of n type semiconductor is adjacent to a region of p type semiconductor, p n junctions play important roles in the operation of all transistors. 

Insulator, amorphous (impurity) Semiconductor (p-n junction) Semiconductor (electron-hole plasma)... 

At larger forward bias, the net photocurrent drops because of increased electron recombination. In a conventional solar cell, the process responsible for the recombination current is normally the same in light and dark, and it is common to make the approximation that J V) = Jsc — - darkC )-Although this may be good for semiconductor p-n junction devices, it is not reliable for dye-sensitized photovoltaic devices. Ionization of the sensitizer opens up a new path for recombination in light, which is not active in dark (Fig. 11). There is some evidence [69] that the reverse current is larger under illumination than in the dark. 

Shottky Diodes. All diodes require at least a small forward bias voltage in order to work. Shottky diodes are fabricated by using a metal-to-semiconductor junction rather than the traditional dual semiconductor p-n junction used with other diodes. Such a construction allows Shottky diodes to operate with extremely low forward bias. 

When a metal is placed in contact with an electrolyte, a potential difference is observed at the liquid-metal interface, as noted in Chapter 2. This is similar to the work-function potential difference which occurs when two dissimilar metals are brought into contact, or the potential difference associated with a semiconductor p n junction. The value of potential difference associated with a metal electrode-electrolyte interface is a function of the metal and contacting electrolyte. Theoretical treatment of this situation is complex and one should refer to a text on electrochemistry such as those by Macinnes (1961) or Newman (1973). Certain types of electrodes are extremely sensitive to various trace impurities in the contacting electrolyte and may react quite differently in seemingly similar circumstances. 

Figure 1. The analogy between semiconductor p-n junction and bilayer molecular rectifiers. In both cases a "forward bias" corresponds to electron flow from left to right.

Figure 21.11 Schematic diagram of a forward-biased semiconductor p-n junction showing (a) the injection of an electron from the n-side into the p-side, and (b) the emission of a photon of light as this electron recombines with a hole.

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