9.3 Materials, Structures and Spin Injection
205
Mg)Te:N and (Zn, Mn)Te:N, instead of Mn ions. Ground-breaking spintronic functionalities have been exhibited and theoretically presented for (Ga, Mn)As and related
systems. Report shows that magnitudes of Curie temperature T C have reached 200 K
in (Ga, Mn)As. The ferromagnetism of (Ga, Mn)As can be controlled by external
electric field, in particular, the critical temperature can be changed with application
an electrical field. It is also an excellent source of polarized electrons, which permits
injection of spins to normal semiconductors.
Now the question is why Mn is so important? Let us have a look on electronic
configurations of Ga, As and Mn.
Ga: [Ar] 3d
10 4s
2 4p
1
As: [Ar] 3d
10 4s
2 4p
3
Mn: [Ar] 3d
5 4s
2 4p
0
• Mn has half filled 3d shell, which leads to S = 5/2 magnetic moment
• Mn has missing 4p electron and hence can act as acceptor (p-type conductor)
Mn has a peculiar property characterized by deep emplacement of the impurity
levels in the valence and conduction bands. As a consequence of that the ferromagnetic order in Mn-based DMS is mediated by carriers present in relatively wide
valence bands, while the d levels of other transition metals reside in the band gap
of III–V and II–VI compounds. In this scenario, spin–spin interactions are dominated. Mn compounds are divalent in II–VI and characterize by S = 5/ 2 and g =
2.0. The spin-dependent hybridization between anion p and Mn d states leads to
the superexchange among the Mn moments, and MnAs or MnTe compounds. This
makes them antiferomagnetic. On the other hand, antiferromagnetic superexchange
can be overcome by ferromagnetic interactions mediated by band holes in DMS. As
an outcome, DMS can turn into ferromagnetic. For III–V compounds, Mn behaves
as an effective mass acceptor (d5 + h) in the case of antimonides and arsenides.
DMS based on wide band gap semiconductor like gallium nitride has drawn an
immense attention as semiconductor spintronics materials as GaN is indisputably
one of the most competent materials for application in electronic and optoelectronic
devices. The remarkable achievement of DMS based on GaN doped with Mn is its
curie temperature, which is above 300 K. Other materials that show room temperature
ferromagnetism are GaMnO, (Cd, Mn)GeP 2 , (Zn, Mn)GeP 2 , ZnSnAs 2 , (Zn, Co)O,
Co(Ti, Sn)O and Eu chalcogenides (see Fig. 9.3).
As far as applications are concerned, the chalcopyrite semiconducting materials
are very promising. As an example, ZnGeP 2 shows strange non-linear optical properties, which can be exploited to design optical oscillators and frequency converters.
ZnSnAs 2 anticipates far-IR generation and frequency conversions. Lattice matching
of wide band gap chalcopyrites, such as ZnGeN 2 and ZnSiN 2 with GaN and SiC,
respectively, and the attainment of ferromagnetism in these materials would enable
for direct integration of magnetic sensors and switches with blue/green/UV lasers
and light-emitting diodes, fabricated in the GaN and SiC.
205
Mg)Te:N and (Zn, Mn)Te:N, instead of Mn ions. Ground-breaking spintronic functionalities have been exhibited and theoretically presented for (Ga, Mn)As and related
systems. Report shows that magnitudes of Curie temperature T C have reached 200 K
in (Ga, Mn)As. The ferromagnetism of (Ga, Mn)As can be controlled by external
electric field, in particular, the critical temperature can be changed with application
an electrical field. It is also an excellent source of polarized electrons, which permits
injection of spins to normal semiconductors.
Now the question is why Mn is so important? Let us have a look on electronic
configurations of Ga, As and Mn.
Ga: [Ar] 3d
10 4s
2 4p
1
As: [Ar] 3d
10 4s
2 4p
3
Mn: [Ar] 3d
5 4s
2 4p
0
• Mn has half filled 3d shell, which leads to S = 5/2 magnetic moment
• Mn has missing 4p electron and hence can act as acceptor (p-type conductor)
Mn has a peculiar property characterized by deep emplacement of the impurity
levels in the valence and conduction bands. As a consequence of that the ferromagnetic order in Mn-based DMS is mediated by carriers present in relatively wide
valence bands, while the d levels of other transition metals reside in the band gap
of III–V and II–VI compounds. In this scenario, spin–spin interactions are dominated. Mn compounds are divalent in II–VI and characterize by S = 5/ 2 and g =
2.0. The spin-dependent hybridization between anion p and Mn d states leads to
the superexchange among the Mn moments, and MnAs or MnTe compounds. This
makes them antiferomagnetic. On the other hand, antiferromagnetic superexchange
can be overcome by ferromagnetic interactions mediated by band holes in DMS. As
an outcome, DMS can turn into ferromagnetic. For III–V compounds, Mn behaves
as an effective mass acceptor (d5 + h) in the case of antimonides and arsenides.
DMS based on wide band gap semiconductor like gallium nitride has drawn an
immense attention as semiconductor spintronics materials as GaN is indisputably
one of the most competent materials for application in electronic and optoelectronic
devices. The remarkable achievement of DMS based on GaN doped with Mn is its
curie temperature, which is above 300 K. Other materials that show room temperature
ferromagnetism are GaMnO, (Cd, Mn)GeP 2 , (Zn, Mn)GeP 2 , ZnSnAs 2 , (Zn, Co)O,
Co(Ti, Sn)O and Eu chalcogenides (see Fig. 9.3).
As far as applications are concerned, the chalcopyrite semiconducting materials
are very promising. As an example, ZnGeP 2 shows strange non-linear optical properties, which can be exploited to design optical oscillators and frequency converters.
ZnSnAs 2 anticipates far-IR generation and frequency conversions. Lattice matching
of wide band gap chalcopyrites, such as ZnGeN 2 and ZnSiN 2 with GaN and SiC,
respectively, and the attainment of ferromagnetism in these materials would enable
for direct integration of magnetic sensors and switches with blue/green/UV lasers
and light-emitting diodes, fabricated in the GaN and SiC.