Surface photovoltage measurements of amorphous Si
films on Si wafers by STM/STS
K. Arima*, T. Shigetoshi*, H. Kakiuchi* and M. Morita*
* Department of Precision Science and Technology, Osaka University, Osaka, Japan
Keywords: surface photovoltage, solar cell, scanning tunneling spectroscopy
Surface photovoltage is investigated on intrinsic hydrogenated amorphous silicon (a-
Si:H) surfaces by scanning tunneling microscopy/ spectroscopy (STM/STS). The
intrinsic a-Si:H film was formed on a p-type Si wafer, and the surface of a-Si:H was
terminated by H atoms with wet treatments. A current- sample bias (I-V) curve shows a
rectifying behaviour in the dark, and the tunneling current increases dramatically only
under the reverse-bias condition with the continuous visible light (630 nm) irradiation,
as shown in Fig. 1(a). This phenomenon is induced
1 by the photoexcited minority carriers that lead to the
change in surface potential of the intrinsic a-
Tunneling current (nA)
0 Si:H.[1] I-V curves both in the dark and under light
irradiation enable us to determine surface
-1
photovoltage, as shown in Fig. 1(b). Figure 2
-2
demonstrates that the surface photovoltage depends
on surface sites. It is likely that the variation of the
-3 (a) magnitude of surface photovoltage is derived from
adsorbates on the surface or sub-surface structure of
-3 -2 -1 0 1 2 3
Vsample (V) the intrinsic a-Si:H. Hence this can be a novel
evaluation of an active layer for solar cells. This
work was partially supported by Nissan Science
Tunneling current (nA)
0.5
photovoltage Foundation.
0.95 V
1.50 V
0.0
-0.5 (b)
-2.0 -1.5 -1.0
Vsample (V) 0.84 V
10 nm
Fig.1. (a) I-V characteristics in the dark
(solid line) and with light irradiation (dotted
line) on a-Si:H. (b) A part of I-V Fig. 2. STM image of a-Si:H on p-type Si
characteristics is magnified to show wafer. At three points in the image,
photovoltage. surface photovoltage is indicated.
1. K. Arima, H. Kakiuchi, M. Ikeda, K. Endo, M. Morita and Y. Mori, Surf. Sci. 572,
449 (2004).
Subject Number: #10, Preference: Poster, E-mail : arima@prec.eng.osaka-u.ac.jp