P-type electric conduction

Kawazoe H., Yasukawa M., Hyodu H., Kurita M., Yanagi H. and Hosono H. (1997), P-type electrical conduction in transparent thin films of CuAlOi , Nature 389, 939-942. 

Thus, a silicon material having a room-temperature p-type electrical conductivity of 50 (D m) must contain 1.60 X 10 at% boron, aluminum, gaUimn, or indium. 

Electrical conductivity is due to the motion of free charge carriers in the solid. These may be either electrons (in the empty conduction band) or holes (vacancies) in the normally full valence band. In a p type semiconductor, conductivity is mainly via holes, whereas in an n type semiconductor it involves electrons. Mobile electrons are the result of either intrinsic non-stoichiometry or the presence of a dopant in the structure. To promote electrons across the band gap into the conduction band, an energy greater than that of the band gap is needed. Where the band gap is small, thermal excitation is sufficient to achieve this. In the case of most iron oxides with semiconductor properties, electron excitation is achieved by irradiation with visible light of the appropriate wavelength (photoconductivity). 

Diamond is electrically a good insulator because of its large band gap (5.47 eV), but the diamond surface grown by CVD was found to be p-type and conducting. 

Electrical conductivity and thermopower measurements on single crystals of t(NHs) tCk (MGS) and (TTF) NiS C H (TTF = tetrathiafulvalene) illustrate the application of electrical property measurements to the study of intermolecular interactions and electronic structure in planar metal complex systems. MGS is an anisotropic, p-type semiconductor conductivity along the metal-chain direction ohm ... 

Figure 10.9. Schematic of the total electric conductivity at different oxygen pressures of an oxidic electrolyte [like case (a) in Figure 10.7]. At extremes in oxygen pressure the compound is an n-type or p-type semiconductor because the mobility of the electronic charge carriers is much higher than that of the ionic charges. When the concentrations of the electronic charge carriers drop below the ionic defect concentrations the compound becomes a mixed conductor. In the electrolytic domain there is no contribution of electrons to the conductivity. From 0. Johannesen and P. Kofstad. Electrical conductivity in binary metal oxides. Part 2. J. Mater. Educ. 7,969 (1985) with permission from the Journal of Materials Education.

The unbonded spot between a silicon atom and a boron atom is a hole that a free electron can occupy. Because this hole attracts an electron, it is viewed as if it were positively charged. Semiconductors that are doped with boron, aluminum, or gallium are p-type semiconductors, the p standing for positive. P-type semiconductors conduct electricity better than pure silicon because they provide spaces that moving electrons can occupy as they flow through the material. 

Betyllium, because of its small size, almost invariably has a coordination number of 4. This is important in analytical chemistry since it ensures that edta, which coordinates strongly to Mg, Ca (and Al), does not chelate Be appreciably. BeO has the wurtzite (ZnS, p. 1209) structure whilst the other Be chalcogenides adopt the zinc blende modification. BeF2 has the cristobalite (SiOi, p. 342) structure and has only a vety low electrical conductivity when fused. Be2C and Be2B have extended lattices of the antifluorite type with 4-coordinate Be and 8-coordinate C or B. Be2Si04 has the phenacite structure (p. 347) in which both Be and Si... 

The electrical conductivity of the water is critical to the correct operation of this type of boiler, and the precise level varies with design and power requirements. However, the conductivity is always relatively low (often specifications require a level of below 15-50 p,S/cm), so demineralized or reverse-osmosis (RO) quality FW is usually specified. 

FIGURE 3.46 In a p-type semiconductor, the electron-poor dopant atoms effectively remove electrons from the valence band, and the "holes" that result (blue band at the top of the valence band) enable the remaining electrons to become mobile and conduct electricity through the valence band. 

Many types of oxide layers have a certain, not very high electrical conductivity of up to 10 to 10 S/cm. Conduction may be cationic (by ions) or anionic (by or OH ions), or of the mixed ionic and electronic type. Often, charge transport occurs by a semiconductor hole-type mechanism, hence, oxides with ionic and ionic-hole conduction are distinguished (in the same sense as p-type and n-type conduction in the case of semiconductors, but here with anions or cations instead of the electrons, and the corresponding ionic vacancies instead of the electron holes). Electronic conduction is found for the oxide layers on iron group metals and on chromium. 

We should note that adsorption of acceptor particles on oxide semiconductors of p-type influences their electric conductivity and work function in the opposite way. As for donor particles such as atmns of H, Na, K, Zn, Cd, Pb, Ag, Fe, Ti, Pt, Pd and many others, their adsorption at medium and low temperatures (when there is no notable diffusion of atoms proper into the crystal and, consequently, there is no substitution of atoms created, the latter obeying the Vervey rule) is always accompanied by increase in electric conductivity and decrease in the work function for semiconductor adsorbent of -type, the opposite being valid in case of p-type adsorbent. 

---