Minority-carrier concentration

Lp = D r ) is the minority carrier diffusion length for electrons in the -region, (0) is the minority carrier concentration at the boundary between the depletion layer and the neutral region. The sign of this equation indicates that electron injection into the -region results in a positive current flow from p to n a.s shown in Figure 7. 

Fig. 5.26. Schematic drawing of the absorption profile, energy bands and diffusion and drift current contributions, together with the minority carrier concentration of an n-type semiconductor under illumination...

It is also important to calculate the eqnilibrinm concentration of holes in a doped n-type semicondnctor and of electrons in a doped p-type semicondnctor. These minority carrier concentrations are readily obtained nsing the concepts described above, becanse equations (5) and (6) are actually more general than has been indicated. As mentioned above, the relationship between n and pi in equation (5) is actually an equilibrium constant relationship between the electron and hole concentrations in the sohd. In the discussion above, this expression was derived under the special constraint that = pi, that is under thermal excitation conditions. However, the equilibrium constant relationship on the right-hand side of equations (5) and (6) must hold regardless of the somce of electrons and holes, so it applies to both doped and intrinsic semiconductor samples. We thus obtain... 

The majority of commercial photovoltaic cells utilize silicon-based technology. When sunlight comes in contact with ap-n diode, the absorbed energy causes promotion of electrons from valence to conduction bands, generating additional electron-hole pairs. The most noticeable result of this excitation is an effective increase in the number of electrons in the conduction band of p-Si (or holes in n-Si, referred to as the minority-carrier concentration). As a result, electrons in the p region will diffuse into the depletion region, where the junction potential propels them back into n-Si vice versa for holes Figure 4.53a). 

Light-sensitive etching is based on the change, due to illumination, in the minority-carrier concentration, which determines the rate of anodic dissolution and corrosion of semiconductors. For example, under illumination of an n-type semiconductor in the anodic polarization regime, the etching rate can be limited by the rate of hole supply to the electrode surface. In darkness, a certain. 

Note that Eq. (3) is indeed of the form of Eq. (2) with = 0. The surface photovoltage depends on the minority carrier concentration at the edge of... 

F. A. Lindholm and J. G. Fossum, Pictorial derivation of the influence of degeneracy and disorder on nondegenerate minority-carrier concentration and recombination current in heavily doped silicon, IEEE Electron Device Lett. EDL-2 (1981) 230-234. 

A voltage exists across the diode when the switch is opened because there are excess carriers within the device. This open-circuit voltage depends on the excess minority carrier concentrations in the quasi-neutral regions at the space-charge region edges. For V(t) kT/q it can be written as [77]... 

The excess minority carrier concentration can be viewed as an additional stationary concentration term that enters the chemical potential although this terminology is strictly only valid in equilibrium. Extending the consideration to a stationary illumination situation where an excess carrier concentration profile exists for a given minority carrier lifetime and for defined boundary conditions, the concept of quasi-Fermi levels can be introduced. Using the Boltzmann... 

Figure III.7 Distribution of minority carrier concentration in illuminated semiconductor/electrolyte contact for different surface concentrations.

There is a single concept behind all of the existing nonequilibrium methods for IR detector performance improvement A modification of charge carrier transport within a photodetector is done with the aim to cause a local equilibrium dismrbance between the carriers and the crystal lattice. This is used to suppress minority carrier concentration below its equilibrium value. As a result, carrier concentration may reach values several orders of magnitude below the equilibrium one at near-room temperatures. As far as the carrier generation-recombination is concerned, the effects of nonequilibrium concentration decrease are equivalent to photodetector cooling. 

Nonequilibrium detectors share a number of similar or even identical characteristics, independently on a particular structure or process. This is a consequence of similar basic principles utilized for nonequilibrium operation. All of the Auger-suppressed devices utilize relatively strong external or internal fields to decrease minority carrier concentration in a given volume and thus operate in the mode of large deviations from equilibrium. The degree of suppression is proportional to the intensity of the applied fields. The structures with the decreased concentration of minority carriers are conventional intrinsic photonic detector strucmres. 

In all nonequilibrium devices presented until now the active region is fabricated in weakly doped v or t material. If a nonequilibrium mechanism is applied the majority concentration in this region decreases near to extrinsic concentration. To maintain electroneutrality, the minority carrier concentration drops several orders of magnitude more. Thus, a nonequilibrium and stationary carrier distribution is reached and dynamically maintained by means of external fields. In such a mode semiconductor behaves again as an extrinsic one. This means that Auger-suppressed devices operate in nonequilibrium mode. 

An equivalent approach to the derivation of boundary conditions is also utilized in the case of isotype junctions, again using the corresponding minority carrier concentrations and expressions (3.71)-(3.72) or (3.73)-(3.74). 

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