Electrical activation donors

N-d Donor doping density Number of electrically active donors per... 

The adsorption of particles of various type results in the change in electric conductivity of such bridges mainly due to local chemical interaction of adsorbed particles with electrically active defects which are electron donors and resulting, thereby, in decrease of their concentration or, on the contrary, in increase due to creation of new defects of this type. In both cases as it has been shown above there are substantially straightforward and easily verified relationships linking both the initial rates in the change of electric conductivity and the stationary values reflecting concentration of adsorbed particles in ambient volume. 

Fig. 5. Capacitance and current transient spectra from -type, CZ grown Si annealed for 18h at 450°C to form the shallow, oxygen thermal donors. (Chantre et al., 1987). Hydrogenation at 200°C passivates the electrical activity of these thermal donors (Chantre et at, 1987).

Hydrogenation also reduces the electrically active concentration of the new oxygen donors (Holzein et al., 1986 Schmalz et al.y 1987). 

In MBE grown GaAs three dominant electron traps are usually observed Ml at c - 0.17 eV, M3 at c - 0.28 eV and M4 at c - 0.45 eV. Exposure of MBE grown material to a hydrogen plasma for 30 minutes at 250°C completely passivates these three deep levels as shown in Fig. 10 (Dautremont-Smith et al., 1986). After five minute anneals at 400°C or 500°C, the passivation remains complete while the shallow donors are fully reactivated. A five minute annealing at 600°C partially restores the electrical activity of M3. Therefore the thermal stability of the neutralization of deep levels in MBE material is much higher than in other materials and is compatible with most technological treatments. 

Before discussing the redistribution of implanted dopants in GaN, it is necessary to briefly review the temperatures required to achieve electrical activity. Pearton et al reported that a temperature of 1100°C is required to achieve electrical activation of Si and Mg + P in GaN [3], However, this temperature is not sufficient to completely remove the implantation induced damage [4], To completely restore the crystal lattice, an annealing temperature of between 1250°C and 1600°C will be required [5], Most of the results on donor redistribution have been for anneals near 1100°C, as discussed in the following sections however, more experimental work must be done at the higher temperatures to characterise the effect of these higher temperatures. The following discussion is separated into common donor impurities (Si and O) and acceptor impurities (Be, Mg, Zn and Ca) in GaN. 

Electrical measurements, mainly temperature-dependent Hall-effect measurements, have been critical in the elucidation of donors and acceptors in ZnO. The main background donors in state-of-the-art VP-grown ZnO have been shown to be H and Al, and the acceptor, Vzn. Other possible donors that must be investigated further are the defects Vo and Znj. Although Vzn seems to be the main electrically active acceptor, still N is evidently present at a much higher concentration. If this is true, then N must be passivated, and the likely passivator is H. Indeed, annealing experiments lead to a much higher acceptor concentration, presumable due to the... 

At least in some cases, a low Eox facilitates the generation and/or injection of a positive charge carrier from the CGL (see above). A low qx also makes it unlikely that an impurity might have a much lower value and act as a trap for holes [44h. For obvious reasons, the cation radicals of these compounds must be stable in the CTL environment, and some of the better donors indeed form remarkably stable radical-ion salts, even in fluid solution [44a]. The CTM must be highly soluble in the polymeric host and the solvent used to fabricate the CTM. It must provide a high concentration of electrically active moieties without plasticizing the host polymer excessively. Compounds that meet these requirements are typically rather large and flexible, and they may contain more than one electrically independent moiety per molecule, e.g., 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC) in Scheme 2. 

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