452
16 Polarized Semiconductors
(a)
P
E ext
P sp =0
(b)
P
E ext
P sp
(c)
P
E ext
P sp
Fig. 16.1 Schematic representation of the polarization versus external electric field dependence for a dielectric, b
pyroelectric and c ferroelectric semiconductors
(a)
P
E
P
P
(b)
P
P 1
2
n 12
P
Fig. 16.2 a Surface polarization charges σ P on a slab of semiconductor material with polarization. The electric field is
given by E = −P// 0 . b Polarization charge σ P at an interface between two semiconductors with different polarization.
In the depicted situation σ is negative
0
0.02
0.04
-0.02
-0.04
-0.06
-0.08
-0.10
0.20 0.25 0.30 0.35 0.40 0.45 0.50
0.373
0.383
0.375 0.377 0.379 0.381
u
P
(C/m )
sp
2
AlN
AlN
TlN
TlN
InN
InN
GaN
GaN
BN
BN
BP
BP
GaP
GaP
AlP
TlP
BAs
AlAs
AlAs
2H-SiC
2H-SiC
BSb
AlSb
AlP
TlP
BAs
BSb
ZnO
ZnO
Fig. 16.3 Spontaneous polarization P sp for various semiconductors as a function of the lattice constant a (left) and the
cell-internal parameter u (right). Based on [1487]
For cubic zincblende structure semiconductors, P sp is typically fairly small. The anisotropy of the
wurtzite structure allows for sizeable effects (Fig. 16.3). The main cause is the nonideality of the
cell-internal parameter u (cf. Sect. 3.4.5).