
44-11Photojunction Sensors
e expression for the total current under illumination of an APD contains an additional term for the
ga
in,
M
,
a
s
d
escribed
i
n
t
he
f
ollowing
e
quation:
I M I I M I
o db ds p
= ⋅ + + ⋅ (44.11)
where
I
db
is the bulk dark current
I
ds
is the surface dark current, which can include ohmic components
For
sim
plicity,
al
l
of th
e
da
rk
bu
lk
cu
rrent
is as
sumed
to ex
perience
mu
ltiplication
in Eq
uation
44.11.
Al
though
th
ere
co
uld
be ga
in
as
sociated
wi
th
th
e
su
rface
co
mponents,
th
e
ga
in
sh
ould
be sm
all,
or ne
g-
ligible,
i
n
a
n
i
deal
d
evice
.
44
.5.3.2
Qu
antum Efficiency
e
f
undamental
e
xpression
f
or
t
he
Q
E
o
f
a p
hotodiode
[
2]
a
pplies
to t
he ...