PISCES-2ET and Its Application Subsystems - Stanford Technology ...

Physical Models
Table 3.11
Parameter Si GaAs/Al x Ga 1-x As Ga x In 1-x As y P 1-y Al x In 1-x As
6
6
b p (V/cm) 3.26×10 [18] 2.03×10 [18] 6.4×10 4.5×10
[21]
E eff E ||
m n 1 [18] 1 [19] 1 [20] 1 [21]
m p 1 [18] 1 a 1 1 [21]
a. 2 in [18] but by comparison to the experimental data 1 is more proper.
3.3.1.2 Carrier Temperature Dependent II Models
There are several ways to model the carrier temperature dependent impact ionization. One way is to
map the carrier temperature to an effective electric field, , in replacing in Eq. (3.38) and all the
material parameters in the expression are kept unchanged. The mapping between T c
and E eff is done
through the following formulation (refer to [22]):
E eff =
5
-- k B
---- T c – T
----------------- L
2 q γ L w
(3.39)
where L w = τ w v sat is called the energy relaxation length and γ is an adjustable parameter (for fitting
the experimental data) which can be accessed by the user using impjt.ratio in the model card
(default: 1.0). The second way is to approximate the actual carrier (drift) velocity with their saturation
velocity and to use carrier-temperature dependent ionization rate as follows:
5
6
G
=
α( T n )nv sat, n + α( T p )pv sat,
p
(3.40)
– ⁄ B c
α( T c ) A c e T c
=
(3.41)
where c stands for either n or p. The values of A and B are listed inTable 3.12. This model can be
Table 3.12
electrons
holes
A (cm -1 ) B (K)
6
3.8×10 1.75×10
7
2.25×10 3.26×10
6
6
invoked through parameter imp.nvt in the model card.
PISCES-2ET – 2D Device Simulation for Si and Heterostructures 29