186
7 Electronic Defect States
(a)
(b)
(c)
Fig. 7.6 Energetic position (ionization energy labeled in meV) of various impurities (A: acceptor, D: donor) in a Ge, b
Si and c GaAs. Based on [574]
7.5 Shallow Defects
In Fig. 7.6, the positions of the energy levels of a variety of impurities are shown for Ge, Si and GaAs.
An impurity for which the long-range Coulomb part of the ion-core potential determines the energetic
level is termed a shallow impurity. The extension of the wavefunction is given by the Bohr radius.
This situation is in contrast to a deep level where the short-range part of the potential determines the
energy level. The extension of the wavefunction is then of the order of the lattice constant. A view on
the history of the science of shallow impurity states is given in [572, 573].
We will consider first a group-IV semiconductor, Si, and (impurities) dopants from the groups III
and V of the periodic system. When these are incorporated on a lattice site (with tetrahedral bonds),
there is one electron too few (group III, e.g. B) or one electron too many (group V, e.g. As). The first
case is called an acceptor, the latter a donor. The doping of III–V semiconductors is detailed in [575].
7 Electronic Defect States
(a)
(b)
(c)
Fig. 7.6 Energetic position (ionization energy labeled in meV) of various impurities (A: acceptor, D: donor) in a Ge, b
Si and c GaAs. Based on [574]
7.5 Shallow Defects
In Fig. 7.6, the positions of the energy levels of a variety of impurities are shown for Ge, Si and GaAs.
An impurity for which the long-range Coulomb part of the ion-core potential determines the energetic
level is termed a shallow impurity. The extension of the wavefunction is given by the Bohr radius.
This situation is in contrast to a deep level where the short-range part of the potential determines the
energy level. The extension of the wavefunction is then of the order of the lattice constant. A view on
the history of the science of shallow impurity states is given in [572, 573].
We will consider first a group-IV semiconductor, Si, and (impurities) dopants from the groups III
and V of the periodic system. When these are incorporated on a lattice site (with tetrahedral bonds),
there is one electron too few (group III, e.g. B) or one electron too many (group V, e.g. As). The first
case is called an acceptor, the latter a donor. The doping of III–V semiconductors is detailed in [575].