Abstract
Heterostructures, such as the crystalline silicon
(
c
-
Si
)
/plasma-enhanced chemical vapor deposited (PECVD) hydrogenated amorphous silicon
(
a
-
Si
:
H
)
structure, form a possibility in the development of a low recombination rear contact for photovoltaic devices fabricated from
p
-type
c
-
Si
(
p
)
substrates. To find a good compromise between limited charge carrier recombination at the surface and a limited resistivity of the contact, a sandwich structure, such as
c
-
Si
(
p
)
∕
a
-
Si
:
H
(
i
)
∕
a
-
Si
:
H
(
p
+
)
has been proposed in the past. However, in this letter, we report that whereas a very thin intrinsic
a
-
Si
:
H
layer
(
∼
3
nm
)
may still yield very low values for the surface recombination velocity of low resistivity
(
0.5
-
1.5
Ω
cm
)
c
-
Si
(
p
)
wafers, the surface passivation properties are lost when this intrinsic film is subsequently covered by a PECVD
a
-
Si
:
H
(
p
+
)
layer. This phenomenon suggests that surface recombination does not take place at the
c
-
Si
(
p
)
∕
a
-
Si
:
H
(
i
)
interface, but more likely in the defect-rich PECVD
a
-
Si
:
H
(
p
+
)
material, by tunneling of minority carriers through the thin
a
-
Si
:
H
(
i
)
layer.