%0 Journal Article
%A Nagai, Takehiko
%A Shimamura, Takuya
%A Tanigawa, Kohei
%A Iwamoto, Yuya
%A Hamada, Hiroya
%A Ohta, Nobuyoshi
%A Kim, Shinho
%A Tampo, Hitoshi
%A Shibata, Hajime
%A Matsubara, Koji
%A Niki, Shigeru
%A Terada, Norio
%D 2019
%T Band Alignment of the CdS/Cu2Zn(Sn1–xGex)Se4 Heterointerface and Electronic Properties at the Cu2Zn(Sn1–xGex)Se4 Surface: x = 0, 0.2, and
0.4
%U https://acs.figshare.com/articles/journal_contribution/Band_Alignment_of_the_CdS_Cu_sub_2_sub_Zn_Sn_sub_1_i_x_i_sub_Ge_i_sub_x_sub_i_Se_sub_4_sub_Heterointerface_and_Electronic_Properties_at_the_Cu_sub_2_sub_Zn_Sn_sub_1_i_x_i_sub_Ge_i_sub_x_sub_i_Se_sub_4_sub_Surface_i_x_i_0_0_2_and_0_4/7605377
%R 10.1021/acsami.8b19200.s001
%2 https://acs.figshare.com/ndownloader/files/14120009
%K CZTGSe bottom layer
%K CZTGSe surface
%K Ge-incorporated Cu 2 ZnSnSe 4
%K Se 4 Heterointerface
%K IPES
%K heterointerface
%K hole deficiencies
%K Fermi level
%K UPS
%K CBO
%K VBO
%K bulk
%K Se 4 Surface
%K laser-irradiated XPS
%K CdS
%K band alignment
%K inversed photoemission spectroscopies
%X The
surface electronic properties of the light absorber and band alignment
at the p/n heterointerface are key issues for high-performance heterojunction
solar cells. We investigated the band alignment of the heterointerface
between cadmium sulfide (CdS) and Ge-incorporated Cu2ZnSnSe4 (CZTGSe), with Ge/(Ge + Sn) ratios (x) between
0 and 0.4, by X-ray photoelectron, ultraviolet, and inversed photoemission
spectroscopies (XPS, UPS, and IPES, respectively). In particular,
we used interface-induced band bending in order to determine the conduction
band offset (CBO) and valence-band offset (VBO), which were calculated
from the core-level shifts of each element in both the CdS overlayer
and the CZTGSe bottom layer. Moreover, the surface electronic properties
of CZTGSe were also investigated by laser-irradiated XPS. The CBO
at the CdS/CZTGSe heterointerface decreased linearly, from +0.36 to
+0.20 eV, as x was increased from 0 to 0.4; in contrast,
the VBO at the CdS/CZTGSe heterointerface was independent of Ge content.
Both UPS and IPES revealed that the Fermi level at the CZTGSe surface
is located near the center of the band gap. The hole concentration
at the CZTGSe surface was on the order of 1011 cm–3, which is much smaller than that of the bulk (∼1016 cm–3). We discuss the differences in hole deficiencies
near the surface and in the bulk on the basis of laser-irradiated
XPS and conclude that hole deficiencies are due to defects distributed
near the surface with densities that are lower than in the bulk, and
the Fermi level is not pinned at the CZTGSe surface.
%I ACS Publications