Semiconductors hosted

In summary, the H-acceptor pairs appear to be very similar to their silicon counterparts, which we have discussed in depth. The H-donor pairs are similar in that the H occupies a silicon-antibonding site however, this is an antibonding site to the defect and not to the host as is found in silicon. It is also interesting to note that the computed hydrogen frequencies appropriate to the latter pairs are better described by theory than the silicon counterparts discussed earlier. It is not clear whether this is a consequence of the electronic-structure method used here, a natural consequence of the differences between the silicon and compound-semiconductor hosts, or simply an accident. 

In the case of semiconductors doped with f elements a different kind of an energy transfer process can be observed, namely from extended band states or excitonic states to the highly localized f-element states. Such a process is different from the cases discussed in the preceding sections, where the energy transfer from point defects (or at the most molecular states) was considered. The interest in semiconductors doped with f elements is obvious, because of their potential to combine sharp f-element luminescence with the possibility of simple electrical excitation via the semiconductor host. However, a quenching of the luminescence with... 

Fig. 20. Energy back-transfer model describing the energy transfer between the semiconductor host and the lanthanide ion R3+ (Culp et al., 1997 Takarabe et al., 1995).

A first test of this model was performed with pressure experiments on InP Yb3+. Here the Yb3+ ion introduces an electron trap to the semiconductor host. The pressure-induced shift of the 2F5/2 -> 2Ft/2 intra 4f shell transitions amounts to 0.96 meV/GPa up to 4 GPa (Stapor et al., 1991), while the bandgap energy of InP increases by 85 meV/GPa (Trommer et al., 1980). 

Magneto-optical properties of doped materials. Paramagnetic dopants can exhibit exchange interactions with the carriers inside the semiconductor host. Such materials are referred to as dilute magnetic... 

Phosphors are composed of a semiconductor host and an activator, and both the host and the activator absorb and transfer excitation energy to the excited state of the activator. Double-perovskite A2B(MoAV)Oe with a monoclinic or pseudo-cubic structure, are substantially absorbed in the NUV region [22]. The excitation spectra of the double-perovskite SraCaWOgiEu exhibit a broad absorption band to blue light in the NUV region. This phenomenon occurs because of the charge-transfer (CT) transitions of O to W in the WOg octahedral and the/-/electronic transitions of the Eu activators. 

Among the techniques that can be used to introduce well defined concentrations of impurities into semiconductors, ion implantation turns out to possess particularly attractive properties. It is not dependent on the diliiisivity nor the solubility of the dopant atom in the semiconductor host, the substrate does not have to be heated as in a diffusion process, the dosage and the depth distribution of the impurity can be well controlled. On the other hand, in those first years around 1960 when the... 

Although ion implantation received its main impetus as a technique to dope semiconductors, its use was not limited to this field. When implanting high enough fluencies in semiconductors, it was found that the technique could be used to synthesise conductive layers at well-defined depth inside the semiconductor host, opening a semiconductor technology field of study of its own. 

For semiconductors the story is quite different. Many defects created in the collision cascade are not mobile which can result in defect configurations that do not anneal at room temperature. Heating to higher temperatures is often necessary to anneal out most damage. But it is not unlikely that the implanted atom or part of them remains part of a defect structure. Figure 6.6 illustrates defect recovery after implantation and annealing a semiconductor host. 

Substitutional defects are either impurities or antisites. Impurities , as one would expect, refers to atoms which are not constituents of the semiconductor host. They are not intrinsic to the nature of a solid, but result from its incomplete purification or intentional contamination. Thus, they are referred to as extrinsic defects. Antisites, as with vacancies, are intrinsic to compounds. Antisite defects are found only in crystals with more than one sublattice and having different atoms on each. Si has two sublattices, both fee Bravais lattices, translated by 1/4, 1/4, 1/4 with respect to each other. However, because the atoms on both are the same, moving a Si atom from one sublattice to the other has no effect. By contrast, GaAs has two sublattices, one on which only Ga atoms reside, the other contains only As. Thus, there are two antisite defects, a Ga on an As site (GaAs) or an As on a Ga site (Asoa)- Antisite defects may, and often do, have multiple charge states in the energy gap. 

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