574
21 Diodes
Fig. 21.59 Schematic
band diagram of a
n-AlGaAs/p-GaAs diode a
without contact of the nand p-materials, b in
thermodynamic
equilibrium, and c with
graded Al composition at
the heterointerface
(a)
p-CuI
n-ZnO
eV =1.0eV
bi
E =3.4eV
g
E =-1.9eV
C
E =-2.2eV
V
E =3.1eV
g
E F
E p
E n
(b)
Fig. 21.60 a Schematic band diagram of a p-CuI/n-ZnO diode. Adapted from [1782]. b j V -characteristics (room
temperature) of type-II epitaxial CuI/ZnO heterojunction bipolar diode (symbols) and fit (red dashed line) with j s =
2×10 −8 A/cm 2 and ideality factor n = 1.8. The other fit (blue line) takes into account additionally a barrier inhomogeneity
and the series resistance. Adapted from [1784]
causes the applied voltage to drop over the entire structure [1785–1787] (Fig. 21.61c) while in a
typical silicon diode for sufficient forward bias (and moderate injection, cmp. Fig. 21.50) flat-band
conditions are present (Fig. 21.61b). The first organic homodiode was reported only in 2005 for zincphthalocyanine (ZnPc) doped with [Ru(terpy) 2 ]
0 (n-type) and F 4 -TCNQ (p-type, cmp. Fig. 18.7b)
[1788]. Deviation from ideal Shockley behavior is discussed in this report.
The hole injecting contact is often made from ITO, the electron injection contact from low work
function metals such as Al, Mg or Ca. Specially designed layers for efficient charge injection (HIL,
hole injection layer [1789] and EIL, electron injection layer [1790]) can be introduced between the
contact metal and the transport layers (Fig. 21.62c). The particular level lineup of the HTL and HTL
as shown in Fig. 21.61c (also Fig. 21.62a) leads to a barrier for electrons and holes. The hole and/or
electron blocking is beneficial for recombination in the vicinity of the interface and prevents exciton
diffusion to the contacts. In organic light emitting diodes (Sect. 23.3.7) an additional layer (EML,
emission layer) designed for efficient radiative recombination (Sect. 18.6) is introduced between HTL
and ETL (Fig. 21.62b).
21 Diodes
Fig. 21.59 Schematic
band diagram of a
n-AlGaAs/p-GaAs diode a
without contact of the nand p-materials, b in
thermodynamic
equilibrium, and c with
graded Al composition at
the heterointerface
(a)
p-CuI
n-ZnO
eV =1.0eV
bi
E =3.4eV
g
E =-1.9eV
C
E =-2.2eV
V
E =3.1eV
g
E F
E p
E n
(b)
Fig. 21.60 a Schematic band diagram of a p-CuI/n-ZnO diode. Adapted from [1782]. b j V -characteristics (room
temperature) of type-II epitaxial CuI/ZnO heterojunction bipolar diode (symbols) and fit (red dashed line) with j s =
2×10 −8 A/cm 2 and ideality factor n = 1.8. The other fit (blue line) takes into account additionally a barrier inhomogeneity
and the series resistance. Adapted from [1784]
causes the applied voltage to drop over the entire structure [1785–1787] (Fig. 21.61c) while in a
typical silicon diode for sufficient forward bias (and moderate injection, cmp. Fig. 21.50) flat-band
conditions are present (Fig. 21.61b). The first organic homodiode was reported only in 2005 for zincphthalocyanine (ZnPc) doped with [Ru(terpy) 2 ]
0 (n-type) and F 4 -TCNQ (p-type, cmp. Fig. 18.7b)
[1788]. Deviation from ideal Shockley behavior is discussed in this report.
The hole injecting contact is often made from ITO, the electron injection contact from low work
function metals such as Al, Mg or Ca. Specially designed layers for efficient charge injection (HIL,
hole injection layer [1789] and EIL, electron injection layer [1790]) can be introduced between the
contact metal and the transport layers (Fig. 21.62c). The particular level lineup of the HTL and HTL
as shown in Fig. 21.61c (also Fig. 21.62a) leads to a barrier for electrons and holes. The hole and/or
electron blocking is beneficial for recombination in the vicinity of the interface and prevents exciton
diffusion to the contacts. In organic light emitting diodes (Sect. 23.3.7) an additional layer (EML,
emission layer) designed for efficient radiative recombination (Sect. 18.6) is introduced between HTL
and ETL (Fig. 21.62b).