538
21 Diodes
Fig. 21.18 a Effective barrier height versus ideality factor for Ag/n-Si Schottky diodes prepared on Si(111) surface with
(7 × 7) reconstruction or unreconstructed (1 × 1) as labeled. The more ideal (1 × 1) surface exhibits the higher barrier.
The dashed lines are linear fits. b Effective barrier height versus ideality factor for Au/n-Si Schottky diodes prepared
on HF-dipped (1 × 1) unreconstructed (001) and (111) surfaces. The dashed lines are linear fits and extrapolation to
n = n if . Both surface orientations exhibit the same extrapolated homogeneous barrier height. Based on data compiled
in [1728]
Fig. 21.19 Calculated
effective Richardson
constant A ∗∗ as a function
of the electric field for a
metal-Si diode at
T = 300 K for a (n-type or
p-type) doping of
10 16 cm −3 . Adapted
from [1732]
140
120
100
80
60
40
20
0
5
10
50
100
500
2
Si
20
200
electrons
holes
Tunneling Current
At high doping the width of the depletion layer becomes small and tunneling processes become more
probable. Also at low temperatures, when thermionic emission is very small, tunneling processes can
dominate the transport between metal and semiconductor. One process is tunneling of electrons close to
the Fermi level of the semiconductor. This process is called field emission (F) and is at least important
for degenerate semiconductors at very low temperatures. If the temperature is raised, electrons are
excited to higher energies where they encounter a thinner barrier. The tradeoff between thermal energy
and barrier width selects an electron energy E m above the conduction-band edge for which the current
is largest. This process is known as thermionic field emission (TF). For very high temperatures enough
carriers can overcome the barrier completely and we are back in the thermionic emission regime. The
21 Diodes
Fig. 21.18 a Effective barrier height versus ideality factor for Ag/n-Si Schottky diodes prepared on Si(111) surface with
(7 × 7) reconstruction or unreconstructed (1 × 1) as labeled. The more ideal (1 × 1) surface exhibits the higher barrier.
The dashed lines are linear fits. b Effective barrier height versus ideality factor for Au/n-Si Schottky diodes prepared
on HF-dipped (1 × 1) unreconstructed (001) and (111) surfaces. The dashed lines are linear fits and extrapolation to
n = n if . Both surface orientations exhibit the same extrapolated homogeneous barrier height. Based on data compiled
in [1728]
Fig. 21.19 Calculated
effective Richardson
constant A ∗∗ as a function
of the electric field for a
metal-Si diode at
T = 300 K for a (n-type or
p-type) doping of
10 16 cm −3 . Adapted
from [1732]
140
120
100
80
60
40
20
0
5
10
50
100
500
2
Si
20
200
electrons
holes
Tunneling Current
At high doping the width of the depletion layer becomes small and tunneling processes become more
probable. Also at low temperatures, when thermionic emission is very small, tunneling processes can
dominate the transport between metal and semiconductor. One process is tunneling of electrons close to
the Fermi level of the semiconductor. This process is called field emission (F) and is at least important
for degenerate semiconductors at very low temperatures. If the temperature is raised, electrons are
excited to higher energies where they encounter a thinner barrier. The tradeoff between thermal energy
and barrier width selects an electron energy E m above the conduction-band edge for which the current
is largest. This process is known as thermionic field emission (TF). For very high temperatures enough
carriers can overcome the barrier completely and we are back in the thermionic emission regime. The