10. Appendix

696 Appendix D
Effects of Isotopic Substitution on Phonons
During the pass 15 years isotopically pure constituents of many semiconductors
have become available at affordable prices. With them it has become possible
to grow semiconductor crystals with tailor-made isotopic compositions.
A number of interesting experiments have thus become possible. In p. 117
(footnote) it has already been mentioned that elimination of strongly neutron
absorbing isotopes (e.g. 113Cd) allows INS measurements on cadmium compounds
such as CdS. Isotopic substitution also yields information about anharmonic
effects, among others the dependence of the lattice parameters on
isotopic mass. The interested reader should consult:
N. Vast and S. Baroni: Effects of Isotopic Disorder on the Raman Spectra of
Crystals: Theory and ab initio Calculations for Diamond and Germanium.
Phys. Rev. B61, 9387–9392 (2000).
M. Cardona and M. L. W. Thewalt: Isotope Effects on Optical Spectra of Semiconductors.
Rev. Mod. Phys 77, 1173–1224 (2005).
Electron Phonon Interactions
In Sect. 3.3 we have discussed the effects of phonons on the electronic states
on the basis of semi-empirical models of the electronic band structures and the
lattice dynamics. As expected, these effects can also be calculated using the ab
initio approach from both the electronic band structures and lattice dynamics.
Such calculations are the simplest for long wavelength acoustic phonons; they
correspond to the effects of uniform (either uniaxial or hydrostatic) strains on
the electronic band structure. More general electron-phonon interaction effects,
including intervalley scattering, have since been calculated also by ab
initio techniques. We mention two recently articles on this subject.
S. Sjakste, V. Tyuterev and N. Vast: Ab initio Study of °-X intervalley scattering
in GaAs under pressure. Phys. Rev. B74, 235216–235222 (2006).
S. Sjakste, N. Vast, V. Tyuterev: Ab initio Method for Calculating Electron-
Phonon Scattering Times in Semiconductors: Application to GaAs and GaP.
Phys. Rev. Lett. 99, 236405–236408 (2007).
Chapter 4
The study of defects in semiconductors is one of the most important fields
in semiconductor physics and new developments appear constantly. For example,
it has been found that large band gap semiconductors tend to be n-type.
It was thought that there might be fundamental reasons preventing the incorporation
of acceptors in them. By now it has been demonstrated via the
p-doping of GaN and related alloys that no insurmountable barriers exist to
prevent the p-doping of the large band gap semiconductors. This breakthrough