epdf.pub_nanotechnology-and-nanoelectronics-materials-devic

3.3 Applications of Nanodefects in Crystals 29
Fig. 3.17 Activation energies of the two traps in Fig. 3.16 derived from Eqs. 3.5 and 3.6
erf
ts
r
1
1
I / I
R
F
(3.8)
r is identical to one of the minority carrier lifetimes, n and p , or to a combination
of both. Therefore, each attempt to accelerate the switching times must
concentrate on the shortening of the lifetimes n and p . Technically this is
achieved by the introduction of point defects or defects of small dimensions in the
critical zone of the semiconductor. N T is assumed as their density and c n or c p their
probability of capture of electrons or holes (c n and c p are related to the initial cross
section c n,p = v th n,p , where v th is the thermal velocity). The theory of Shockley,
Hall, and Read shows that the lifetime is related to the number of traps by
1
n,
p
(3.9)
N
c
n , p
T
Traps in a power device also lead to unfavorable effects. This includes the rise of
the forward resistance and the leakage current in the reverse state.
The traps can be brought into the semiconductor in different ways. Early procedures
have been gold or platinum doping, or electron and gamma ray exposure.
Today, best results are obtained by hydrogen implantation.