17.3 Diluted Magnetic Semiconductors
469
Fig. 17.5 Computed
values of the Curie
temperature T C for various
p-type semiconductors
plotted versus the band gap
(dashed lines are guides to
the eye). All materials
contain 5% Mn on the
cation sublattice and a hole
concentration of
p = 3.5 × 10 20 cm −3 .
Values for T C taken
from [1532]
are analyzed theoretically in [1536] and are predicted to exhibit less-stable ferromagnetism than III–V
semiconductors of comparable band gap.
The carrier density and thus magnetic properties in a DMS can be controlled in a space-charge region
(cf. Sect. 21.2.2) as demonstrated in [1537]. In Fig. 17.6, results are shown for hydrogen- (deuterium-)
passivated GaMnAs that exhibits ferromagnetism as ‘as-grown’ thin film. The deuterium is incorporated
in similar concentration as the Mn, assumes a back-bond position (forming a H–As–Mn complex) and
compensates the hole gas from the Mn (cf. Sect. 7.9). The low-temperature conductivity drops nine
orders of magnitude [1538]. Such material displays only paramagnetic behavior. An optimal Mn
concentration for ferromagnetic Ga 1−x Mn x As is around x = 0.05. For smaller Mn concentrations, the
hole density is too small and the Curie temperature drops; for larger Mn concentrations, the structural
properties of the alloy degrade (phase separation into GaAs and MnAs.
3 ).
Magnetic hysteresis has been found in nearly compensated Mn-doped ZnO [1539, 1540] (Fig. 17.7).
Such material is interesting due to its small spin-orbit coupling. The exchange mechanism is under
debate.
Fig. 17.6 Magnetization M versus magnetic field H for Ga 0.963 Mn 0.037 As at low temperature. a Comparison of asgrown (full squares) and deuterated (open circles) thin film with magnetic field in the layer plane at T = 20 K. b
Magnetization of the deuterated sample at T = 2 K for larger magnetic fields. Solid line is Brillouin function for g = 2
and S = 5/2. Adapted from [1538]
3 MnAs is a ferromagnetic metal. MnAs clusters can be a problem since they create ferromagnetic properties but not in
the way the DMS is supposed to work.
469
Fig. 17.5 Computed
values of the Curie
temperature T C for various
p-type semiconductors
plotted versus the band gap
(dashed lines are guides to
the eye). All materials
contain 5% Mn on the
cation sublattice and a hole
concentration of
p = 3.5 × 10 20 cm −3 .
Values for T C taken
from [1532]
are analyzed theoretically in [1536] and are predicted to exhibit less-stable ferromagnetism than III–V
semiconductors of comparable band gap.
The carrier density and thus magnetic properties in a DMS can be controlled in a space-charge region
(cf. Sect. 21.2.2) as demonstrated in [1537]. In Fig. 17.6, results are shown for hydrogen- (deuterium-)
passivated GaMnAs that exhibits ferromagnetism as ‘as-grown’ thin film. The deuterium is incorporated
in similar concentration as the Mn, assumes a back-bond position (forming a H–As–Mn complex) and
compensates the hole gas from the Mn (cf. Sect. 7.9). The low-temperature conductivity drops nine
orders of magnitude [1538]. Such material displays only paramagnetic behavior. An optimal Mn
concentration for ferromagnetic Ga 1−x Mn x As is around x = 0.05. For smaller Mn concentrations, the
hole density is too small and the Curie temperature drops; for larger Mn concentrations, the structural
properties of the alloy degrade (phase separation into GaAs and MnAs.
3 ).
Magnetic hysteresis has been found in nearly compensated Mn-doped ZnO [1539, 1540] (Fig. 17.7).
Such material is interesting due to its small spin-orbit coupling. The exchange mechanism is under
debate.
Fig. 17.6 Magnetization M versus magnetic field H for Ga 0.963 Mn 0.037 As at low temperature. a Comparison of asgrown (full squares) and deuterated (open circles) thin film with magnetic field in the layer plane at T = 20 K. b
Magnetization of the deuterated sample at T = 2 K for larger magnetic fields. Solid line is Brillouin function for g = 2
and S = 5/2. Adapted from [1538]
3 MnAs is a ferromagnetic metal. MnAs clusters can be a problem since they create ferromagnetic properties but not in
the way the DMS is supposed to work.