Carrier intrinsic concentration

In an intrinsic semiconductor, charge conservation gives n = p = where is the intrinsic carrier concentration as shown in Table 1. Ai, and are the effective densities of states per unit volume for the conduction and valence bands. In terms of these densities of states, n andp are given in equations 4 and... 

As the temperature increases, the intrinsic carrier concentration rises exponentially so that at some point n ... 

Parker [55] studied the IN properties of MEH-PPV sandwiched between various low-and high work-function materials. He proposed a model for such photodiodes, where the charge carriers are transported in a rigid band model. Electrons and holes can tunnel into or leave the polymer when the applied field tilts the polymer bands so that the tunnel barriers can be overcome. It must be noted that a rigid band model is only appropriate for very low intrinsic carrier concentrations in MEH-PPV. Capacitance-voltage measurements for these devices indicated an upper limit for the dark carrier concentration of 1014 cm"3. Further measurements of the built in fields of MEH-PPV sandwiched between metal electrodes are in agreement with the results found by Parker. Electro absorption measurements [56, 57] showed that various metals did not introduce interface states in the single-particle gap of the polymer that pins the Schottky contact. Of course this does not imply that the metal and the polymer do not interact [58, 59] but these interactions do not pin the Schottky barrier. 

For an n-type semiconductor, if the donor impurity concentration is much greater than the intrinsic carrier concentration, Nd >nj, then no Nd. Equation (3.4.9) can then be written as... 

Material Cubic lattice constant, pm Band gap, eV Intrinsic carrier concentration, cm-3 Relative dielectric constant, 8 Mobility, Electrons cm2/(Vs) Holes... 

As the temperature increases, the intrinsic carrier concentration rises exponentially so that at some point n p rather than n Nd+. Likewise, as the temperature falls, Ea — Ev becomes large compared with KT and carrier freeze-out occurs below about 100 K so that n Nd+ < Nd. All of this assumes that n < Nc or p < Nv> corresponding to Ep in the energy gap. When enough donor atoms are added so that n > 10 Nc the Fermi level moves... 

Indium nitride is a wide-gap semiconductor with negligible intrinsic carrier concentration and there are no reports of deliberate doping. Electron concentrations, most commonly of order 1020 cm 3, appear independent of growth method and are therefore assumed to be of native defect origin. The presence of... 

To describe the conductivity of an intrinsic semiconductor sample quantitatively, we need to calculate the concentrations of both types of charge carriers in the solid. The key quantity that controls the equilibrium concentration of electrons and holes in an intrinsic semiconductor is the band gap. Because the thermal excitation energy required to produce an electron and a hole is equal to Eg, the intrinsic carrier concentrations can be related to Eg using the Boltzmann relationship ... 

For most semiconductors, kT (0.0259 eV at 300 K) is much smaller than E. Thus, few electrons and holes are produced at room temperature in such semiconductors. Intrinsic samples are far too resistive for many applications additionally, in actual semiconductor samples, the concentration of unwanted impurities often exceeds the intrinsic carrier concentrations. Under these conditions, it is difficult to maintain quality control over the electrical properties of semiconductors. For these reasons, the conductivity of semiconductors is generally deliberately controlled through a process known as doping. 

Because the intrinsic carrier concentrations in semiconductors are so low, even impurity concentrations at the level of one part per billion can have a profound effect on the electrical properties of a semiconductor sample. To increase the sample conductivity and to control other electronic properties of the semiconductor, low concentrations of specific impurity atoms are often introduced into the crystal lattice. This process, which is called doping, serves to decrease the resistance... 

The intrinsic carrier concentration due to thermal excitation across the gap... 

Again taking the effective masses to be equal to the electron mass, using 300 K for room temperature, and using 2.7 eV for the energy gap of the ladder-type PPPs, we obtain an intrinsic carrier concentration of 10 4 cm 3. This value will rise to 41 cm-3 upon increasing the temperature to 400 K. These values have to be compared to common inorganic semiconductors at room temperature 2.7... 

Silicon carbide-based sensors can operate at higher temperatures (above 600°C) because of a wide band gap and low intrinsic carrier concentration availability of SiC. Taking advantage of this trait, silicon carbide semiconductors have been used... 

This expression is derived from the more general case where the electron and hole concentrations in the conduction and valence bands are n and p with np = n2. At RT, taken as 300 K, the intrinsic carrier concentration n is 1.1 x 10111 cm in silicon, but it increases to about 4 x 1013 cm 3 in germanium to reach 2 x 1016 cm-3 in intrinsic InSb. 

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