Carrier majority

In n type semiconductors, electrons are tire majority carriers. Holes will also be present tlirough accidental incoriioration of acceptor impurities or, more importantly, tlirough tlie intentional creation of electron-hole pairs. Holes in n type and electrons in p type semiconductors are minority carriers. 

Some of tliese problems are avoided in heterojunction bipolar transistors (HBTs) [jU, 38], tlie majority of which are based on III-V compounds such as GaAs/AlGaAs. In an HBT, tlie gap of tlie emitter is larger tlian tliat of tlie base. The conduction and valence band offsets tliat result from tlie matching up of tlie two different materials at tlie heterojunction prevent or reduce tlie injection of tlie base majority carriers into tlie emitter. This peniiits tlie use of... 

Germanium single crystals intended for electronic apphcations are usuaHy specified according to conductivity type, dopant, resistivity, orientation, and maximum dislocation density. They may be specified to be lineage-free unless the specified resistivity is below about 0.05 H-cm. Minority carrier lifetime and majority carrier mobHity are occasionaHy specified. 

The impurity atoms used to form the p—n junction form well-defined energy levels within the band gap. These levels are shallow in the sense that the donor levels He close to the conduction band (Fig. lb) and the acceptor levels are close to the valence band (Fig. Ic). The thermal energy at room temperature is large enough for most of the dopant atoms contributing to the impurity levels to become ionized. Thus, in the -type region, some electrons in the valence band have sufficient thermal energy to be excited into the acceptor level and leave mobile holes in the valence band. Similar excitation occurs for electrons from the donor to conduction bands of the n-ty e material. The electrons in the conduction band of the n-ty e semiconductor and the holes in the valence band of the -type semiconductor are called majority carriers. Likewise, holes in the -type, and electrons in the -type semiconductor are called minority carriers. 

For a weU-designed, weU-made HgCdTe photoconductoi detector (76,77), g-r noise is dominant and may be expressed in terms of a minority carrier densityp and majority carrier density n. Semiconductor noise analysis for the HgCdTe photoconductor yields,... 

Under both short-circuit and open-circuit conditions, a solar cell produces no electric power, the power is consumed internally in the cell and is dissipated as heat. When a resistive load is connected to a cell in sunlight, a photogenerated voltage, F, is induced across the load and a current flows through it. The existence of requites that the flow of majority carriers be reduced from that in the open-circuit condition there must be a higher battier potential than in the open-circuit case (Fig. 2d). This higher barrier potential (V6 — ) indicates a smaller reduction from Since the photogenerated... 

The photogenerated current is in the same direction as /, but is always less than because the battier potential under load conditions is always less than F, which results in a larger flow of majority carriers than that in a short-circuited cell. Thus, when a solar cell is under load, the current and voltage are always less than and lU, respectively this condition is the curve-factor loss. Depending on the characteristics of the particularp—n junction and on the cell operating conditions, there is an optimal load resistance that maximizes the power output of the cell, ie, the product of its current and voltage. 

The equihbtium lever relation, np = can be regarded from a chemical kinetics perspective as the result of a balance between the generation and recombination of electrons and holes (21). In extrinsic semiconductors recombination is assisted by chemical defects, such as transition metals, which introduce new energy levels in the energy gap. The recombination rate in extrinsic semiconductors is limited by the lifetime of minority carriers which, according to the equihbtium lever relation, have much lower concentrations than majority carriers. Thus, for a -type semiconductor where electrons are the minority carrier, the recombination rate is /S n/z. An = n — is the increase of the electron concentration over its value in thermal equihbtium, and... 

Fig. 4. Charge distributions in the voltage-biased MOS capacitor (a) accumulation of majority carriers near surface (b) depletion of majority carriers from...

Fig. 6. An abmpt p—n junction in thermal equiUbiium (a) space—charge distribution where (-) indicate majority carrier distribution tails and the charge...

When electrons are injected as minority carriers into a -type semiconductor they may diffuse, drift, or disappear. That is, their electrical behavior is determined by diffusion in concentration gradients, drift in electric fields (potential gradients), or disappearance through recombination with majority carrier holes. Thus, the transport behavior of minority carriers can be described by a continuity equation. To derive the p—n junction equation, steady-state is assumed, so that = 0, and a neutral region outside the depletion region is assumed, so that the electric field is zero. Under these circumstances,... 

The electron current in such devices is much smaller than, and fully masked by, the current of the majority carriers. For this reason, AI/Oocl-OPV5/Ca devices... 

LDL is the major carrier of cholesterol to the periphery and supplies the cholesterol essential for the integrity of nerve tissue, steroid hormone synthesis, and cell membranes. The association between elevated plasma cholesterol carried in LDL and the risk of coronary heart disease has been well established. LDL is also sometimes called the bad cholesterol. 

It is well known that photoelectrochemical measurements do not indicate photocurrents in the accumulation region of an illuminated semiconductor. The reason is that majority carriers control interfacial reactions, which... 

This means that the minority carriers are measured, however formally, with an effectively changed mobility, which also includes the mobility of photogenerated majority carriers. 

We conclude that the interfacial kinetics of excess majority carriers control the PMC signal in the accumulation region, while it is the minority carriers, as we have seen, that control the PMC signal in the depletion region. 

---