N-type conductivity

Diamond may never be used to make devices because it is nearly impossible to make it sufficiently n type, tliat is to obtain high electron concentration. Substitutional B is a good shallow acceptor, and interstitial Li has been reported to produce some n type conductivity. 

Aqueous cathodic electrodeposition has been shown to offer a low-cost route for the fabrication of large surface n-CdS/p-CdTe solar cells. In a typical procedure, CdTe films, 1-2 xm thick, are electrodeposited from common acidic tellurite bath over a thin window layer of a CdS-coated substrate under potential-controlled conditions. The as-deposited CdTe films are stoichiometric, exhibit strong preferential (111) orientation, and have n-type conductivity (doping density typically... 

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. 

G. Xiong, J. Wilkinson, B. Mischuck, S. Tiizemen, K.B. Ucer, and R.T. Williams, Control of p- and n-type conductivity in sputter deposition of undoped ZnO, Appl. Phys. Lett., 80 1195-1197, 2002. 

For correct function of the ISFET, a sufficiently large gate voltage, Vq, must be applied between the leads to the reference electrode and to the substrate, so that a sufficiently large potential difference is formed between the surface and the interior of the substrate for formation of the n-type conductive channel at the insulator/substrate interface. This channel conductively connects drain 1 and source 2, which are connected with the substrate by a p-n transition. On application of voltage Vj between the drain and the source, drain current /p begins to pass. Under certain conditions the drain current is a linear function of the difference between Vq and the Volta potential difference between the substrate and the membrane. 

One would expect the presence of trapped electrons in the oxidized samples to give rise to n-type conductivity, conduction possibly taking place by jump migration of the odd electron in the lattice of Cr + ions in a somewhat similar manner to the mechanism discussed by Heikes 174) for the migration of Ni + holes in lithia-doped NiO. The observed p-type conductivity of chromia in an oxygen atmosphere is presumably due to electron holes in a solid which is predominantly CraOs for the low concentrations of chromia-on-alumina where the 7-phase resonance intensity is maximum, the chromium is predominantly in the d-6 valence state 167). 

The IV-VI films are usually p-type, both as deposited and after annealing in air. One study, where PbS was deposited from a bath containing hydrazine, found the deposit on glass to be n-type temporarily but converted to p-type on air exposure. By depositing the PbS on a trivalent metal coating (such as Al), the n-type conductivity could be stabilized for a longer time. 

The earliest of these studies was on PbS. PbS can have either p- or n-type conductivity, although CD PbS is usually p-type. Based on the belief that the p-type conductivity may be due to alkali metal cations from the deposition solution, an alkali metal—free deposition, using lead acetate, thiourea, and hydrazine hydrate was used [33]. While initially n-type, the film converted to p-type in air. Attempts to stabilize the p-type material by adding trivalent cations to the deposition solution were unsuccessful. However, deposition of the PbS on a trivalent metal, such as Al, did stabilize the n-PbS, at least for a time. In this way, p-n junctions were made (the PbS close to the trivalent metal was n-type, while the rest of the film was p-type). Photovoltages up to 100 mV were obtained from these junctions at room temperature and almost 300 mV at low temperatures (90 K). 

In the Bi-doped PbS (donor doping), the transition of electron to hole conduction is shifted to higher Ps. and the region of n-type conduction extends to a higher Ps.- In region (II), the concentration of carrier n ( = [Bipb]) is weakly dependent on Ps.-... 

A similar experiment was performed on the crystals grown by the method of liquid phase epitaxy (LPE) as the starting crystal. The starting crystals were reheated under various pressures of As gas at 850 °C for 30 min. Figure 3.38 shows the hole concentration, p, dependence on Pas at the surface of the heat-treated crystals. (The starting crystals showed n-type conduction, and after heat-treatment under this condition, only 7 pm of the surface of... 

The discussion draws on the extensive studies by Philips researchers [7] and [8] and by D.M. Smyth and co-workers [4], Several cases of oxide systems in which the conductivity is controlled by the substitution of aliovalent cations are given in Chapter 4. For instance, Sb5+ can replace Sn4+ in SnC>2 and be compensated by an electron in the conduction band conferring n-type conductivity (see Section 4.1.4). However, models for oxide systems are generally more complex than for... 

Electrical conductivity of metals is very high and is of the order of 106 108 ohm-1 cm-1 while that of insulators is of the order of 10-12 ohm-1 cm-1. Semi-conductors have intermediate conductivity which lies in the range 102 10-9 ohm-1 cm1. Electrical conductivity of solids may arise through the motion of electrons and positive holes (electronic conductivity) or through the motion of ions (ionic conductivity). The conduction through electrons is called n-type conduction and through positive holes is called p-type conduction. Pure ionic solids where conduction can take place only through motion of ions are insulators. However, the presence of defects in the crystal structure increases their conductivity. 

So far, all observed free-charge-carrier contributions to the optical properties of ZnO and related materials are only due to n-type conductivity, because reproducible and sufficiently high p-type conductivity is still a challenge. Therefore, all data presented here address n-type conductive samples. 

Fig. 7.14. Resistivity vs. carrier concentration at 300 K of undoped and doped PLD ZnO thin films on sapphire [56]. The legend gives the maximum concentrations of the dopant oxides in the ZnO targets in weight-%. The optimized ZnO films show lower intrinsic n-type conductivity. For each dopant element, series of films grown at different PLD oxygen pressures are included...

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