SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

80 CHAPTER 2. ELECTRONIC LEVELS IN SEMICONDUCTORS

x

Semiconductor

Insulator

Device channe l

with free

carriers

E 2

E 1

• 
  


• –


• –

V(x) =

Interface electric

field Es =

enS

TRIANGULAR QUANTUM WE LL FORM ED IN ELECTRONIC DEVICES

eEsx

s

Figure 2.34: A schematic of free electrons (conduction electrons) in a semiconductor device
confined to an approximately triangular quantum well.

2.11 STRAINED HETEROSTRUCTURES

As noted in chapter 1 it is now possible to incorporate strain into an epitaxial film. In fact,
strain of a few percent can be built-in simply by growing a film on a mismatched substrate. ne of
the most important strained heterostructure is the SiGe/Si structure. This system is compatible
with Si based technology since it uses Si substrates. Due the modifications in the bandstructure
high performance SiGe electronic devices can be made. Other important strained structures are
InGaAs grown on GaAs or InP substrates and the AlGaN/GaN structure.
Once the strain tensor is known, we are ready to apply the deformation potential theory to
calculate the effects of strain on various eigenstates in the Brillouin zone. The strain perturbation
Hamiltonian is defined and its effects are calculated in the simple first order perturbation theory.
In general we have

Hαβ=

∑

ij

Dαβijij (2.11.1)

whereDijis the deformation potential operator which transforms under symmetry operations as
a second rank tensor.Dαβij are the matrix elements ofDij.