530
21 Diodes
(a)
(b)
Fig. 21.11 a Capacitance versus probing frequency f for a Pd/ZnO Schottky diode (zero bias) at T = 85 K. Theoretical
dependence (solid line) and experimental data (circles). b Capacitance of the same diode as a function of temperature
(thermal admittance spectroscopy, TAS) for four different probing frequencies f =10, 50, 100 and 316 kHz (ac amplitude
50 mV). Arrows denote the release of carriers from four different defect levels, two shallow ones and the well-known
defects E1 and E3 [737, 1707]. The inset shows the contribution of the E1 defect, indicated by a rectangle in the main
graph, in more detail. Symbols are experimental data, lines are fit with four-level model (E1: E D = 116 meV, E3:
E D = 330 meV) [1708]
Fig. 21.12 Transport
mechanisms at
metal-semiconductor
junctions. (1) Thermionic
emission (‘above’ the
barrier) (2) tunneling
(‘through’ the barrier), (3)
recombination in the
depletion layer, (4) hole
injection from metal
E C
E V
E F
E F
(1)
eV
(3)
(2)
(4)
with higher energies, are distinguished. Also, recombination in the depletion layer and hole injection
from the metal are possible.
The transport of electrons above the barrier can be described with diffusion theory [1709, 1710] or
thermionic-emission theory [576]. A detailed treatment can be found in [1711, 1712]. In both cases the
barrier height is large compared to kT . For thermionic emission (typically relevant for semiconductors
with high mobility) the current is limited by the emission process and an equilibrium (constant electron
quasi-Fermi level) is established throughout the depletion layer and ballistic transport is considered. In
diffusion theory (for low mobility) a thermal equilibrium between metal and semiconductor electrons
is established in the interface plane and the current is limited by diffusion and drift in the depletion
region.
Thermionic Emission
The current density per unit area j s→m of electrons that flow from the semiconductor into the metal is
due to the hot electrons from the thermal distribution function
j s→m = −e
∞
E F +F Bn
v x dn .
(21.36)
21 Diodes
(a)
(b)
Fig. 21.11 a Capacitance versus probing frequency f for a Pd/ZnO Schottky diode (zero bias) at T = 85 K. Theoretical
dependence (solid line) and experimental data (circles). b Capacitance of the same diode as a function of temperature
(thermal admittance spectroscopy, TAS) for four different probing frequencies f =10, 50, 100 and 316 kHz (ac amplitude
50 mV). Arrows denote the release of carriers from four different defect levels, two shallow ones and the well-known
defects E1 and E3 [737, 1707]. The inset shows the contribution of the E1 defect, indicated by a rectangle in the main
graph, in more detail. Symbols are experimental data, lines are fit with four-level model (E1: E D = 116 meV, E3:
E D = 330 meV) [1708]
Fig. 21.12 Transport
mechanisms at
metal-semiconductor
junctions. (1) Thermionic
emission (‘above’ the
barrier) (2) tunneling
(‘through’ the barrier), (3)
recombination in the
depletion layer, (4) hole
injection from metal
E C
E V
E F
E F
(1)
eV
(3)
(2)
(4)
with higher energies, are distinguished. Also, recombination in the depletion layer and hole injection
from the metal are possible.
The transport of electrons above the barrier can be described with diffusion theory [1709, 1710] or
thermionic-emission theory [576]. A detailed treatment can be found in [1711, 1712]. In both cases the
barrier height is large compared to kT . For thermionic emission (typically relevant for semiconductors
with high mobility) the current is limited by the emission process and an equilibrium (constant electron
quasi-Fermi level) is established throughout the depletion layer and ballistic transport is considered. In
diffusion theory (for low mobility) a thermal equilibrium between metal and semiconductor electrons
is established in the interface plane and the current is limited by diffusion and drift in the depletion
region.
Thermionic Emission
The current density per unit area j s→m of electrons that flow from the semiconductor into the metal is
due to the hot electrons from the thermal distribution function
j s→m = −e
∞
E F +F Bn
v x dn .
(21.36)