146
6 Band Structure
6.3.4 GaP
GaP (Fig. 6.10b) is an indirect compound semiconductor. The conduction-band minima are along the
100 directions.
6.3.5 GaN
GaN (Fig. 6.11) is a direct semiconductor that has wurtzite structure but can also occur in the metastable
cubic (zincblende) phase.
6.3.6 Lead Salts
The band gap of PbS (Fig. 6.12), PbSe and PbTe is direct and located at the L point. The lead chalcogenide system shows the anomaly that with increasing atomic weight the band gap does not decrease
monotonically. At 300 K, the band gaps are 0.41, 0.27 and 0.31 eV for PbS, PbSe and PbTe, respectively.
15
10
5
0
-5
15
10
5
0
-5
-10
W
X
GaN
zb
w
Fig. 6.11 Band structure of GaN (direct) in zincblende (zb) modification (left) and wurtzite (w) modification (right),
both displayed in the wurtzite Brillouin zone to facilitate comparison
Fig. 6.12 Calculated band
structure of PbS (direct).
The energy gap is at the L
point. The forbidden band
is shown in grey. Adapted
from [468]