Biasing the Junction

With a positive voltage V is applied to the p-type material. Equation 21.10 maybe written as 

Forward-biased p-n junction. Applying a plus voltage to the p-material reduces the contact potential and raises the effective Fermi level allowing more electrons to diffuse from the n-side to the p-side. 

Carrier distribution and related electric field in a forward-biased p-n junction. The number of holes that were injected at the edge of the depletion zone on the n-side is given by p exp (eV/kT) where is the hole density in the n-material away from the junction region. Note also that the electric field has been reduced by 2V/Xn. 

Pp)x is the hole concentration in the p-type material at the edge of the space charge region 

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Schematic showing the operation of a solid state laser. In the unbiased state (a) the Fermi level lies above the conduction band in the n-side and below the valence band on the p-side. (b) Biasing the junction lifts the filled states in the conduction band in the n-region above the above empty states below the valence band in the p-side, thus inverting the electron population.

Schematic of the energy bands of a double heterojunction laser. The Fermi level is above the conduction band edge in the n-AlGaAs and below the valence band in the p-GaAs. Forward biasing the junction (below) causes the electrons to spill over into the active p-GaAs region where they are confined by the higher bandgap AlGaAs. The confined inverted population in the active region promotes stimulated emission.

The silicon diode (photodiode) detector consists of a strip of p-type silicon on the surface of a silicon chip (n-type silicon). By application of a biasing potential with the silicon chip connected to the positive pole of the biasing source, electrons and holes are caused to move away from the p-n junction. This creates a depletion region in the neighbourhood of the junction which in effect becomes a capacitor. When light strikes the surface of the chip, free... 

Tunneling electric current through the normal metal insulator superconductor junction is accompanied with heat flow out of normal metal when property voltage is biased. The phenomenon enables cooling of electrons and phonons (under special conditions) in the region below 1K. At lower bath temperatures, two parasitic heat sources decrease refrigerator performance ... 

The most common method of generating LED emission is via the injection of minority carriers toward the depletion region at the junction by forward-biasing a pn... 

Quantum-state decay to a continuum or changes in its population via coupling to a thermal bath is known as amplitude noise (AN). It characterizes decoherence processes in many quantum systems, for example, spontaneous emission of photons by excited atoms [35], vibrational and collisional relaxation of trapped ions [36] and the relaxation of current-biased Josephson junctions [37], Another source of decoherence in the same systems is proper dephasing or phase noise (PN) [38], which does not affect the populations of quantum states but randomizes their energies or phases. 

Since the Hamiltonian for atoms in accelerated optical lattices is similar to the Legett Hamiltonian for current-biased Josephson junctions [37], the present theory has been extended to describe effects of current modulations on the rate of macroscopic quanmm tunneling in Josephson junctions in Ref. [11]. 

A silicon-semiconductor-radiation detector of a layer of p-type silicon in contact with a layer of n-type Si is shown in Figure 18.15. What happens when this p-n junction is created The electrons from the n-type silicon will migrate across the junction and fill the holes in the p-type silicon to create an area around the p-n junction in which there is no excess of holes or electrons. (We say that a depletion region has been formed around the junction.) Imagine that we apply a positive voltage to the n-type material and a negative voltage to the p-type material (the junction is said to be reverse biased). The electrons will be pulled farther... 

We have thus far talked about the chemisorption of ions at the semiconductor/electrolyte interface and charge transfer in the semiconductor surface layer. The main charge transfer process of interest is the transfer of electrons and holes across the semiconductor/electrolyte interface to the desired electrolyte species resulting in their oxidation or reduction. For any semiconductor, electrode charge transfer can occur with or without illumination and with the junction biased in the forward or reverse direction. 

Under normal operation, the emitter-base junction is forward biased, whereas the collector-base junction is reverse biased (Figure 11). The voltage across the emitter-base junction is varied by an input signal. Because the donor concentration in the emitter is higher than the acceptor concentration in the emitter, the current through the junction is primarily due to electrons injected into the base. The base width is smaller than the mean... 

Here Vj, is the built-in potential (Fig. C.3). When an external potential is applied, two situations may develop. First, if the polarity of the applied potential follows the polarity of the junction (i.e., positive potential to p-type and negative to n-type) the junction is said to be forward biased and a current will flow. 

In-depth selective etching of silicon in alkaline solutions can also utilize the different passivation potentials between p- and -type materials in alkaline solutions such asK0H, " EDP," NH40H, " hydrazine, " " " andTMAH. In this method, as shown in Fig. 7.62(9), an anodic voltage sufficient to cause passivation of n-Si is applied via an ohmic contact. Due to the potential drop in the reversely biased/in junction, the p-Si is maintained at a potential negative to the passivation potential and is etched. On complete removal of the p-Si, the junction disappears and the etch stops because the n-Si is passivated. A current peak, corresponding to the formation of the... 

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