V-type semiconductors

Composting facilities, 25 873-874 Compound III-V type semiconductors, 23 15 Compounded flavors, 72 47 Compounded perfumes, 78 354 Compound gauge, 20 646 Compounding... 

Exclusion of minority carriers in narrow-bandgap semiconductors was demonstrated in a temperature range of 180-295 K, exclusively in the middle wavelength infrared range, i.e., in the range (3-5) pm. Most of the reported experiments were performed on v-type semiconductors [243]. 

Fig. V-14. Energy level diagram and energy scales for an n-type semiconductor pho-toelectrochemical cell Eg, band gap E, electron affinity work function Vb, band bending Vh, Helmholtz layer potential drop 0ei. electrolyte work function U/b, flat-band potential. (See Section V-9 for discussion of some of these quantities. (From Ref. 181.)...

Figure 9.9 Impurity levels I in (a) an n-type and (b) a p-type semiconductor C is the conduction band and V the valence band...

Finally cells containing a p-type semiconductor electrode should be mentioned. In principle the application of p-type electrodes would be even more favorable because electrons created by light excitation are transferred from the conduction band to the redox system. Stability problems are less severe because most semiconductors do not show cathodic decomposition (see e.g. earlier review article. However, there is only one system, p-InP/(V " /V ), with which a reasonable efficiency was obtained (Table 1) . There are mainly two reasons why p-electrodes were not widely used (i) not many materials are available from which p-type electrodes can be made (ii)... 

Figure 7. Quantum efficiency versus potential at various p-type semiconductors in a DMF-0.1 JVf TBAP solution containing 5% water under a C02 atmosphere. Monochromatic light of 600 nm was used for p-Si, p-InP, p-GaAs, and p-CdTe, while light of 400 nm was used for p-GaP.103 Scan rate 0.1 V/r...

The WS2 electrodes represent n- and p-type semiconductors that behave relatively ideally (15,16) with respect to interface energetics in that the value of Ey does vary with Ere(jox according to equation (1) for Erenox within 0.8 V of Epg. 

The Schottky-Mott theory predicts a current / = (4 7t e m kB2/h3) T2 exp (—e A/kB 7) exp (e n V/kB T)— 1], where e is the electronic charge, m is the effective mass of the carrier, kB is Boltzmann s constant, T is the absolute temperature, n is a filling factor, A is the Schottky barrier height (see Fig. 1), and V is the applied voltage [31]. In Schottky-Mott theory, A should be the difference between the Fermi level of the metal and the conduction band minimum (for an n-type semiconductor-to-metal interface) or the valence band maximum (for a p-type semiconductor-metal interface) [32, 33]. Certain experimentally observed variations of A were for decades ascribed to pinning of states, but can now be attributed to local inhomogeneities of the interface, so the Schottky-Mott theory is secure. The opposite of a Schottky barrier is an ohmic contact, where there is only an added electrical resistance at the junction, typically between two metals. 

In theory, the III-V compound semiconductors and their alloys are made from a one to one proportion of elements of the III and V columns of the periodic table. Most of them crystallize in the sphalerite (zinc-blende ZnS) structure. This structure is very similar to that of diamond but in the III-V compounds, the two cfc sublattices are different the anion sublattice contains the group V atoms and the cation sublattice the group III atoms. An excess of one of the constituents in the melt or in the growing atmosphere can induce excess atoms of one type (group V for instance) to occupy sites of the opposite sublattice (cation sublattice). Such atoms are said to be in an antisite configuration. Other possibilities related with deviations from stoichiometry are the existence of vacancies (absence of atoms on atomic sites) on the sublattice of the less abundant constituent and/or of interstitial atoms of the most abundant one. 

Volkman, S. Mattis, B. Molesa, S. Lee, J. Vombrock, A. Bakhishev, T. Subramanian, V. 2004. A novel transparent air-stable printable n-type semiconductor technology using ZnO nanoparticles. Proceedings from IEDM 04 (San Francisco, CAj.pp. 32.1.1-32.1.4. 

The high-pressure region is associated with the electroneutrality equation [h ] = 2[V ]. Holes predominate, so that the material is a p-type semiconductor in this regime. In addition, the conductivity will increase as the g power of the partial pressure of the gaseous X2 component increases. The number of metal vacancies (and nonmetal excess) will increase as the partial pressure of the gaseous X2 component increases and the phase will be distinctly nonstoichiometric. There is a high concentration of cation vacancies that would be expected to enhance cation diffusion. 

Figure 7.5 Mott-Schottky plot for the depletion layer of an n-type semiconductor the flat-band potential Eft, is at 0.2 V. The data extrapolate to Eft, + kT / eo-...

Fig. 10-10. Polarization curves for electrode reactions at n-type and p type semiconductor electrodes in the dark and in a photoezdted state dashed curve = dark solid curve = photoexcited V (i )= anodic (cathodic) current in the dark tpi, (t ) = anodic (cathodic) current in a photoexcited state.

---