Degenerated semiconductor

Another class of conducting oxides are degenerate semiconductors, obtained by heavy doping with suitable foreign atoms. Two oxides, n-Sn02 (doped with Sb, F, In) and n-ln203 (doped with Sn), are of particular interest. These are commercially available in the form of thin optically... 

Degenerate semiconductors can be intrinsic or extrinsic semiconductors, but in these materials the band gap is similar to or less than the thermal energy. In such cases the number of charge carriers in each band becomes very high, as does the electronic conductivity. The compounds are said to show quasi-metallic behavior. 

Electrical measurements of the luiOs (ITO) films gave temperature-independent resistivities (p) of 2 X 10 (10 ) ff-cm, carrier concentrations (N ) of 2 X 10 ° (10 ) cm, and mobilities (pi) of 3 (17) cm V sec The temperature independence of the resistivity indicated that the films, even the nominally undoped ones, were degenerate semiconductors. 

Fig. 1.13 Electron density of states N(E) in a cubic material F denotes the Fermi energy (a) normal metal (b) semimetal (c) insulator, (d) n-type degenerate semiconductor.

Since both metals and degenerate semiconductors have been used as the counter-electrode to the semiconductor in both diode and capacitor-type devices, a more general notation than that usually found in the literature will be employed in this review. This more generalized notation will refer to the counter-electrode as the conductor (c). Hence, M-S, M-I-S, and degenerate semiconductor-interfacial layer-semiconductor diode devices all become C-S or C-I-S... 

The diamond films specific resistance (p) depends on the boron content and varies, e.g., from some 104 2 cm at a boron concentration of 1018 cm 3 to a value of tenths and even thousandths of 2 cm for boron concentration as high as 1021 cm 3. Correspondingly, diamond changes its nature, starting as a dielectric, then sequentially converting to a semiconductor, degenerate semiconductor, and finally a quasimetal. 

The bulk electronic properties of extrinsic semiconductors are largely determined by the level of doping that is used to make the materials n-type or p-type. For non-degenerate semiconductors, the electron concentration in the conduction band and the hole concentration in the valence band are related to the Fermi energy EF and to the effective densities of states in the conduction and valence bands (Nc and Ny respectively) by... 

According to equation (12.17), the fluxes of electrons and holes are driven by concentration and potential gradients. This distinction is a result of the separation of the chemical and electrical contributions given in equation (12.15). If desired, degenerate semiconductor conditions can be modeled by calculating the value of the activity coefficients f for electrons and holes as described by Hwang and Brews and Bor ham and Orazem. The flux expression for species i is constrained by the equation of continuity, i.e.. 

For a non-degenerated semiconductor (n-type or p-type), the carriers are electrons... 

Fig. 2 shows the temperature dependence of <7 for the FGM and the components. The 7 value of all the samples monotonously decreased with an increase of temperature, indicating that the samples are the typical degenerated semiconductors. The 7 value for the FGM was almost intermediate between those for the components and never become lower than those of the components in spite of the existing interface resistivity. At Ti>500 K, the O value for FGM was larger than that for the components. 

The structure of this equation and its curves with N(T) given either by Equation 4 or 5 do not depend generally on dimensionality, d the values for the parameters for the three dimensionalities are of course different, but the evolution of the curves from the semiconductive state to the semimetallic state is the same for all three dimensions. Hence, Equation 5 can be used in Equation 7 to illustrate the predictions of the model. Such is shown in Figure 5 wherein a(T) / cr(200) is plotted for E = 10 eV, n = 1, and Ef is varied from 0 to 2 x 10 eV. In this8sequence, the curves vary from that for a semiconductor at ji to that for a semimetal (a degenerate semiconductor) at d. If curve a were extended to higher temperatures, then it would display a broad maximum, or minimum in the resistivity. The maximum is attributable to the competition... 

Surface biphonons could be investigated, for example, by the attenuated total reflection (ATR) method. In contrast to RSL by polaritons, this method is effective, as is well known, both for crystals with and without inversion center. In this sense, it is a more universal method. In conclusion we point out that in degenerate semiconductors Fermi resonance with plasmons (47) is also possible along with Fermi resonance with phonons and polaritons. The spectrum of plasmophonons has been measured in many semiconductors by the RSL method (see, e.g. Mooradian and McWhorter (48)). 

Photogalvanic cells Molecular pigment in solution Metal (or degenerate semiconductor)-electrolyte Electrical... 

Electrical properties of junctions formed between superconducting material, S, and a non-superconducting metallic material, N, which may be a metal or a degenerate semiconductor, are determined by special boundary conditions. If we consider a superconductor-semiconductor (S-N) interface with high transparency, a proximity effect is observed due to injection of electron pairs (Cooper pairs) from the superconductor into the semiconductor where they decay over a characteristic length, the induced coherence length. 

Progress in development of protective coatings for semiconductor photoelectrodes was bound with making use of materials other than metals, with "metallic" conductivity, namely, silicides (of platinum, or ruthenium), or degenerate semiconductors (Sn02 Sb, Sn02 - In203 BP, and others) [43 - 45]. 

Experimental results have been used to obtain averaged activity coefficients.60 Another approach toward characterization of degenerate semiconductors has been to include the nonidealities associated with degeneracy within a modified Nernst-Einstein relationship.61"64 The modified Nernst-Einstein relationship is given by65... 

If the band gap is so small that thermal energy at normal temperatures is sufficient to generate a very high number of charge carriers in each band the material is classed as a degenerate semiconductor. At OK intrinsic semiconductors become insulators. 

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