10.6. MAGNETIC SEMICONDUCTORS AND SPINTRONICS 505
Current, IVoltage, VT > ~T 0
T < T 0 =928.5 KC(aF)80 mV
C(aF)Figure 10.13: A schematic of how current voltage relations change as temperature is raised.
AboveT 0 , defined in the figure, normal ohmic conduction occurs.
have measurable effects. At zero bias there is no net flow of electrons as usual. However at
small biases smaller than the charging energy, an electron cannot move from the left to the right
because that would raise the energy of the right side bye^2 / 2 Cas shown. Once the voltage level
(times electron charge) exceeds the charging energy, electrons can flow across the junction and
we have ohmic behavior. The current–voltage relation shows a highly non-linear behavior as
shown in figure 10.12b.
The effects sketched in figure 10.12b have a strong temperature dependence. As the temper-
ature rises, the distribution of carriers in the contact is smeared by∼kBT. AS a result the
Coulomb blockade effect survives only up to the temperature,T 0 defined above. In figure 10.13
we show how the current-voltage relations change when temperature is raised.
10.6 MAGNETIC SEMICONDUCTORS
AND SPINTRONICS
In most semiconductors the asymmetry between spin up and spin down electrons is negligible
even in presence of a magnetic field. As a result in existing electronic devices the spin of the
electron is not relevant to current flow. The density of spin up and spin down electrons is the
same unless a strong magnetic field is applied to select a particular state. The contacts used to
inject electrons also usually have no spin selectivity. If spin selectivity can be created it should be