SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

2.11. STRAINED HETEROSTRUCTURES 83

1.5

1.0

0.5

0.0

–0.5

0.0 0.2 0.4 0.6 0.8

Ge MOLE FRACTION (x)

BAND

EDGE

(eV)

[001] 6-fold degenerate unstrained

SiGe conduction band

Bands when SiGe is strained

by Si substrate

[100][010]

HH

LH

SH

Figure 2.36: Epitaxial strain induced splittings of the conduction band and valence band as a
function of alloy composition for Si 1 −xGexgrown on (001) Si. UCB: unstrained conduction
band, HH: heavy hole, LH: light hole, SH: split-off hole.

0.5

0.4

0.3

0.2

0.1

0.0

–2.0 –1.0 0.0 1.0 2.0

m

*/m

0

ε(%)

Figure 2.37: Change in the density of states mass at the valence bandedges as a function of strain
for the Al 0. 3 Ga 0. 7 As/InGaAs system.