Acceptors neutral

Another consequence of acceptor neutralization is the disappearance of excitons bound to acceptors. Their characteristic luminescence can be restored by the thermal release of the hydrogen. 

The earliest evidence for acceptor neutralization was found in the work of Sah et al. (1983, 1984), who attributed the neutralization effect to a bonding between H and B. This hypothesis inspired our search for the B—H vibrational mode, to be described in Section V. Our model of H binding to Si near a B atom aroused some controversy from Pearton (1984) that required additional definitive tests by Pankove et al. (1984b). 

At low temperatures, donors and acceptors remain neutral when they trap an electron hole pair, forming a bound exciton. Bound exciton recombination emits a characteristic luminescence peak, the energy of which is so specific that it can be used to identify the impurities present. Thewalt et al. (1985) measured the luminescence spectrum of Si samples doped by implantation with B, P, In, and T1 before and after hydrogenation. Ion implantation places the acceptors in a well-controlled thin layer that can be rapidly permeated by atomic hydrogen. In contrast, to observe acceptor neutralization by luminescence in bulk-doped Si would require long Hj treatment, since photoluminescence probes deeply below the surface due to the long diffusion length of electrons, holes, and free excitons. 

As for silicon, secondary ion mass spectrometry (SIMS) is the most widely used profiling analysis technique for deuterium diffusion studies in III-V compounds. Deuterium advantageously replaces hydrogen for lowering the detection limit. The investigations of donor and acceptor neutralization effects have been usually performed through electrical measurements, low temperature photoluminescence, photothermal ionization spectroscopy (PTIS) and infrared absorption spectroscopy. These spectroscopic investigations will be treated in a separated part of this chapter. 

Fig. 8. Comparison of the deuterium and active acceptor concentration profiles in a deuterated GalnAs/InP Zn structure showing that the acceptor neutralization exactly extends through the deuterium penetration region (( = 20 min., r=163°C, rf power density = 0.08 W/cm2). J. Chevallier et al., Materials Science Forum, 38-41, 991 (1989). Trans. Tech. Publications.

The line at 2287.7 cm"1 in InP visible in Fig. 18 is clearly the same as the one observed in plasma diffused sample by Pajot et al. (1989) and which is the spectroscopic evidence of the zinc acceptor neutralized by hydrogen. The line at 2272 cm"1 observed only in InP doped with manganese is very... 

Bronsted-Lowry concept (14) An acid-base concept that defines an acid as a proton donor and a base as a proton acceptor. Neutralization is the transfer of a proton from an acid to a base. 

However, the protolytic theory cannot explain the distinctly acid or base properties of numerous substances which are not able to either split-off or accept a proton. This stimulated G. N. Lewis (1923) to a different generalization of the notion of acids and bases. According to the Lewis theory a base is a substance which is the donor of a free electron pair, whereas, acid can bond a free electron pair of another particle and thus, it is its acceptor. Neutralization of an acid by base is conditioned by the formation of coordination (donor-acceptor) bond. The Lewis theory is of importance particularly in the chemistry of coordination compounds where all central... 

A. hydronium ion. . . proton donor. . . proton acceptor. . . neutralize. .. conjugate... 

Failure of traditional copolymerization equations to predict the composition of the terpolymers from donor-acceptor-neutral monomer ternary mixtures brought about the thought that these systems might be amenable to evaluation as copolymerization of a CTC (complexomer) with neutral monomer. In other words, polymerization of a three monomer... 

Using the CTC equilibrium constants (table in the appendix to this chapter) it is possible to calculate the true reactivity values for the CTC and for the neutral monomer. Raetzsch and coworkers used this procedure for the cyclopentene-MA and norbornene-MA copolymerizations with acrylonitrile (Table 10.23). The same technique was also used to determine the reactivity constants for several other donor-acceptor-neutral monomer polymerizations (Table 10.23). For the NVP-MA-methyl methacrylate system the true reactivity ratios show the NVP-MA CTC is about 3 000 times the reactivity of NVP and 600 times the reactivity of methyl methacrylate toward the propagating radical ending in methyl methylacrylate.Results of this type support the concept of alternating copolymerization of a CTC with neutral monomer. 

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