Free-carrier concentration

For a junction of a conjugated polymer, which has an energy gap of around 3 eV (around the value of the polyphenylenes) and a free carrier concentration n> 1017 cm-3, with a low workfunction metal (e.g. when [Pg.155]

Photoelectrochemical techniques have been utilized to determine the minority (electron) diffusion length (L) and other electrical parameters of p-ZnTe [125] and p-type Cdi-jcZnjcTe alloys [126]. In the latter case, the results for a series of single crystals with free carrier concentration in the range 10 " -10 cm (L = 2-4 xm, constant Urbach s parameter at ca. 125 eV ) were considered encouraging for the production of optical and electro-optical devices based on heterojunctions of these alloys. 

When both donors and acceptors are present, compensation results, whereby the electrons supplied by the donor are given to the acceptor. Thus, the free carrier concentration can be considerably reduced below that expected from introducing a known donor or acceptor if the opposite type of dopant is unintentional. For example, semi-insulating (SI) InP (used as a substrate for epitaxial growth) can be made by incorporating low levels of Fe3+ as a deep acceptor (reduced to Fe2+) to compensate for unintentional n-type doping in the sample [19]. 

In the thermodynamic models (FIAM and BLM), the internalisation flux is assumed to be rate-limiting, and the concentration of carriers or sensitive sites bound by the solute of interest negligible with respect to the total number of carriers (i.e. free carrier concentration constant). The fundamental equations describing the equilibrium models can be summarised as ... 

In the simplest case of a competitive uptake of two metals (or a metal and proton) for an identical uptake site under equilibrium conditions, the reduction of the uptake flux of the solute can be quantitatively predicted using the respective equilibrium formation constants (equations (38) (41)). As can be seen in Table 3, for a given study, constants among the trace metals, protons and alkaline earth metals are often sufficiently similar for competition to be important. Nevertheless, competition is likely to be negligible under most environmentally relevant conditions where competition occurs between low concentrations of metals, such that the free carrier concentration remains approximately equal to the total receptor concentration. 

IR transmission for the porous samples has been ascribed to a reduced free carrier concentration in the porous material due to trapping in surface states. After [Lei4]. 

Electrical conductivity, a, is given by the product of free-carrier concentration, n, carrier mobility, p, and carrier charge, e ... 

The Auger effect at a center can take place in various ways, since the three particles required for the process can be located on the particular center, on another center, and/or in the bands. The case of all three particles located at the center has been well treated fairly recently by Robbins and Dean (1978) and will therefore not be considered further. The remaining cases are those where either one or two particles are free (in one of the bands). For both these situations, the transition probability p depends on the free-carrier concentration it is customarily defined in terms of Auger coefficients and C, respectively, for one and two free carriers. For the case of one free hole,... 

The corrosion behavior of semiconductors can, in principle, be described within the framework of the same concepts as for metals (see, for example, Wagner and Traud, 1938), but with due account for specific features in the electrochemical behavior of a solid caused by its semiconducting nature (Gerischer, 1970). One of the main features is photosensitivity related to a change in the free-carrier concentration under illumination. Photosensitivity underlies the phenomenon of photocorrosion. 

Fig. 3.47 Dependence of the compensation ratio 6 and free carrier concentration n ( = Nu on As source temperature, TXs, for GaAs crystals grown by the Bridgman method. ...

Jhe concentrated (>0.4Af) metal-ammonia solutions were first called metallic" by Kraus in 1921 (7). On several recent occasions the term semiconductor" has implicitly been substituted for metal" in interpreting various data (1, 2). Since Kyser and Thompson (8) have established the truly metallic nature of the solutions by measuring the free carrier concentration, it is worthwhile to re-examine the relative data and interpret it in terms of liquid metal theory. 

Fig. 2. Deuterium (D) and free carrier concentration (n) profiles of a n-type GaAs Si bulk sample exposed to a rf deuterium plasma for 90 min. at 250°C (rf power density = 0.2W/cm2). The loss of free carriers occurring only in.the deuterated region suggests that hydrogen plays a major role in the free carrier concentration decrease. The deuterium concentration drop in the near surface region is attributed to a deuterium out-diffusion during the cooling stage of the sample with the plasma off. J. Chevallier et al., Materials Science Forum, 10-12, 591 (1986). Trans. Tech. Publications.

Fig. 28. Representation of a hydrogenated field effect transistor. The carrier concentration in the active layer is controlled, before the gate deposition, by the hydrogen neutralization of the donors present in the highly silicon doped layer. The insert shows the free carrier concentration gradient from the gate, which results from the hydrogen diffusion. J. Chevallier and M. Aucouturier, Ann. Rev. Mater. Sci. 18, 219 (1988). Annual Reviews Inc.

Semiconductors with free carriers can support SEW. This has been demonstrated for a number of materials, but little use has been made of them as substrates for adsorbed molecules. To illustrate that interesting possibilities exist, Fig. 20 shows the propagation distance for SEW on GaAs as a function of free carrier concentration for a frequency of about 80 cm. These data were taken with a molecular laser.The observed distances are of order 1 cm, sufficient for use with the two prism technique... 

The first investigation of the phonon modes in binary InN was an extrapolation of the Gai-xInxN (0 < x < 1) alloy modes in reflection towards the binary compound [1], A typically high free carrier concentration in the mid 1020 cm 3 range controls the absorption (Drude absorption) in the infrared and must also account for the broadened Reststrahlen band in pure InN films (e.g. in [1]). In this case infrared active phonons couple to the plasma of the free electrons forming phonon-plasmon coupled modes [10,11], However, layers of low carrier concentration have been achieved and pure LO phonon energies have been derived in Raman spectroscopy. Resonant Raman spectroscopy at 514 nm has been performed, assigning five of the six Raman allowed zone centre phonon modes [8,9] (TABLE 1). 

The free carrier concentration at room temperature was determined by Raman experiments using the Ai(LO) phonon-plasmon coupled mode and by the reflectance in the mid-infrared and the optical absorption in the near-infrared range. Each experiment for the GaN layer of 60 pm thickness showed a free carrier concentration in the order of 1017 cm 3. 

Thus, to achieve p-t5q)e doping of ZnO a number of aspects have to be considered. First of all the formation of hydrogen shallow donors has to be prevented or their concentration has to be minimized. Recently it has been shown that a simple post anneal of state-of-the-art ZnO at 850 °C causes the dissociation of hydrogen shallow donors which results in a decrease of the free carrier concentration from 1x10 cm" to 6x10 cm". 

In a reactive sputtering process the oxygen flow rate f(02) is the most relevant parameter. Fig. 1 displays a typical example of the influence of f(02) on physical properties and structure. Hall effect measurements show that the free carrier concentration n decreases continuously with f(02) whereas the electron mobility attains a maximum at medium values of f(02). This variation of the n and p clearly reflects the change from metallic behavior at low f(02) (region I) to oxide formation (region III) at high f(02) which is related with an increase of the optical transmission T. These changes are accompanied by structural variations in the ZnO layers. The SEM... 

IR reflection spectra have been used to study the free carrier concentration and the free carrier lifetime in superconducting systems. As an example. Fig. 4.8-17c shows the... 

The proportionality constant between the applied electric field and the resulting drift velocity is called the charge carrier mobility, jx. For electrons, = q r /ml ), for holes, ftp = 7(Trn/mj ). It should be noted that, owing to differences in the effective masses of electrons and holes, their mobilities within a semiconductor may be markedly different. The electrical conductivity, a, of a semiconductor is related to the free carrier concentrations by ... 

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