6.3 Band Structures of Selected Semiconductors
145
(a)
Si
6
4
2
0
-2
-4
-6
-8
-10
-12
Energy (eV)
L
X U,K
(b)
4
2
0
-2
-4
-6
-8
-10
-12
Energy (eV)
Ge
L
X U,K
Fig. 6.9 Band structure of a silicon (indirect) and b germanium (indirect). In Si, the minima of the conduction band are
in the 100 direction, for germanium in the 111 direction. Adapted from [164], based on [467]
(a)
6
4
2
0
-2
-4
-6
-8
-10
-12
Energy (eV)
GaAs
L
X U,K
(b)
6
4
2
0
-2
-4
-6
-8
-10
-12
Energy (eV)
L
X U,K
GaP
Fig. 6.10 Band structure of a GaAs (direct) and b GaP (indirect). For GaAs the minimum of the conduction band is at
, for GaP in the 100 direction. Adapted from [164], based on [467]
6.3.2 Germanium
Germanium, another elemental semiconductor, (Fig. 6.9b) also has an indirect band structure. The
conduction minima are at the L point in the 111 direction. Due to symmetry there are eight equivalent
conduction-band minima.
6.3.3 GaAs
GaAs (Fig. 6.10a) is a compound semiconductor with a direct band gap since the top of the valence
band and the bottom of the conduction band are at the same position in k space (at the The
next highest (local) minimum in the conduction band is close to the L point.