Figure 6.6 shows the effect of material combination when n 0 ¼ 10
22 /m
3 and
F ¼ 4.25 nN while all other parameters are kept the same as those used for Fig. 6.4.
The results are very close.
The integration of Δn over (0,L) can be used as a measure of the coupling
between F and Δn as in Eq. (3.79). For the composite rod in this section, we are
particularly interested in the effect of h/c rather than L on the coupling between F and
Δn. Therefore we examine the change of number of carriers in the differential
element in Fig. 6.3, i.e., Δn(2cbdz). From Eq. (6.70), for a differential element of
the rod near its ends under unit extensional stress, we have Δn(2cbdz) ffi γ(2cbdz)n 0
which is plotted in Fig. 6.7 versus h/c when h + c is fixed. The curves all have a
Si and PZT-4
Si and PZT-5A
Si and BaTiO 3
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
-1.0
-0.5
0.0
0.5
1.0
Dn (m
-3
)
×10
21
z (mm)
Fig. 6.6 Distribution of
electron concentration
perturbation Δn for different
material combinations
Si and PZT-4
Si and PZT-5A
Si and BaTiO 3
0
1
2
3
4
5
0
2
4
6
8
10
g (2cbdz)n
0
(m
2
/N)
×10
-6
h/c
Fig. 6.7 γ(2cbdz)n 0 versus
h/c for different material
combinations
154
6 Composite Structures