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[20250402_Supporting Information for publication.pdf](https://mdr.nims.go.jp/filesets/6f522cbb-c6f5-4750-b851-471db29ffd6d/download)

## Creator

Xinyi He, Kenji Matsuo, [Takayoshi Katase](https://orcid.org/0000-0002-2593-7487), [Kota Hanzawa](https://orcid.org/0000-0002-0995-9360), Hideto Yoshida, [Shigenori Ueda](https://orcid.org/0000-0001-9425-0614), [Hidenori Hiramatsu](https://orcid.org/0000-0002-5664-5831), [Hideo Hosono](https://orcid.org/0000-0001-9260-6728), Toshio Kamiya

## Rights

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Nano Materials, copyright ©  2025 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsanm.5c00686.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Nanoscale Origin of Strong Charge Carrier Scattering at Grain Boundaries in Orthorhombic SnSe Semiconductor Thin Films](https://mdr.nims.go.jp/datasets/bcfac7a0-012d-4e7c-af86-9a83433e3797)

## Fulltext

S1  Supporting Information Nanoscale Origin of Strong Charge Carrier Scattering at Grain Boundaries in Orthorhombic SnSe Semiconductor Thin Films Xinyi He1,2, Kenji Matsuo1, Takayoshi Katase1,3,*, Kota Hanzawa3, Hideto Yoshida4, Shigenori Ueda5,6, Hidenori Hiramatsu1,3, Hideo Hosono1,and Toshio Kamiya1,3,* 1 MDX Research Center for Element Strategy, Institute of Integrated Research, Institute of Science Tokyo, 4259 Nagatsuta, Midori, Yokohama 226-8501, Japan 2 Kanagawa Institute of Industrial Science and Technology, 705-1 Shimoimaizumi, Ebina, Kanagawa 243-0435, Japan 3 Materials and Structures Laboratory, Institute of Integrated Research, Institute of Science Tokyo, 4259 Nagatsuta, Midori, Yokohama, 226-8501, Japan 4 SANKEN, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan 5 Research Center for Electronic and Optical Materials, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan 6Synchrotron X-ray Station at SPring-8, NIMS, 1-1 Sayo, Hyogo 679-5148, Japan  * Correspondence to: katase.t.aa@m.titech.ac.jp, kamiya.t.aa@m.titech.ac.jp      S2  Contents Fig. S1. Growth rate dependence of electronic properties and crystallinity of SnSe films grown at 500 oC on glass substrates. Fig. S2. X-ray diffraction (XRD) analysis of SnSe films grown at different temperatures on glass substrates. Fig. S3. Atomic force microscopy (AFM) images of SnSe films grown at different temperatures on glass substrates. Fig. S4. Cross-sectional scanning transmission electron microscope (STEM) image of SnSe film grown at 500 oC on glass substrate. Fig. S5. Out-of-plane and in-plane XRD patterns of SnSe film grown at 500 oC on MgO substrate. Fig. S6. AFM image of SnSe film grown at 500 oC on MgO substrate. Fig. S7. Cross-sectional STEM image of SnSe film grown at 500 oC on MgO substrate. Fig. S8. Lattice parameters and volumes of SnSe films.  Fig. S9. Atomic ratio of Sn and Se in SnSe films.  Fig. S10. Arrhenius plots of carrier concentration for SnSe films. Fig. S11. Electronic structure analysis of SnSe films.  Fig. S12. Crystal structure analysis of SnSe models with 1 Sn or 1 Se vacancies.    S3  Optimization of growth rate for SnSe films on glass substrates    Figure S1. Growth rate dependence of room-temperature (RT) electronic properties and crystallinity of SnSe films deposited at 500 oC on glass substrates. (a) electronic conductivity (s), carrier concentration (n), and carrier mobility (µ) vs. growth rate. (b) FWHM values (Dw400) of rocking curves for 400 diffractions for SnSe phase vs. growth rate. (c) AFM images for SnSe films deposited under growth rate of 0.4 nm/s and 2.5 nm/s.      S4  SnSe thin film growth on glass and MgO (001) substrates Figure S2 summarizes XRD patterns of SnSe films deposited by changing the growth temperature (Tg) from RT to 500 oC on glass substrates. For out-of-plane XRD patterns (Fig. S2(a)), only h00 diffraction peaks of SnSe phase were observed even for the films at Tg = RT. The intensity of h00 diffraction peaks became stronger and the peak width became sharper with increase of Tg. The FWHM values of 400 diffraction peaks decreased from 10.5o to 4.8o with increase of Tg (Fig. S2(b)). For in-plane XRD patterns (Fig. S2(c)), the peak intensity of 111 diffraction was strongest for films with Tg = RT, but the intensity of 011, 002, 020, and 022 diffraction peaks increased largely with increase of Tg. From these results, the a-axis orientation was dominant for SnSe films deposited even at RT, but the degree of a-axis orientation increased by increasing Tg up to 500 oC. Figure S3 summarizes AFM images of SnSe films grown on glass substrates. Small crystallites were observed for Tg = RT and 100 oC, while the grain size largely increased with increase of Tg up to 500 oC. Figure S4 shows the STEM images of SnSe film deposited on glass substrate at Tg = 500 oC. The multi-domain structures with different contrast were observed in the cross-sectional STEM image (Fig. S4(a)), where the GBs were clearly observed as indicated by arrows. In the atomic-scale STEM image of SnSe film (Fig. S4(b)), the stacking structure of Sn-Se molecular layers were observed along out-of-plane direction.  Figure S5 shows the out-of-plane and in-plane XRD patterns of SnSe film grown at Tg = 500 oC on MgO (001) substrate.1 The h00 diffraction peaks of SnSe and 00l diffraction peaks of MgO were observed for out-of-plane XRD pattern (Fig. S5(a)), and the 002 diffraction peak of SnSe and 200 diffraction peak of MgO were observed for in-plane XRD pattern (Fig. S5(b)). The FWHM value of 400 diffraction peak was 0.2o (inset of Fig. S5(a)). For in-plane f scan of 002 diffraction of SnSe, diffraction peaks appeared at every 90° and exhibited 4-fold rotational symmetry. However, SnSe has orthorhombic lattice structure, and thus the SnSe was epitaxially grown on MgO substrate with 90° rotational domain structure. The epitaxial relationship was  S5  [100] SnSe || [001] MgO for out-of-plane direction and [010][001]SnSe || MgO [100] for in-plane direction. From AFM image of the SnSe epitaxial film (Fig. S6), the spiral domain growth was observed, where the average domain size was ~100 nm. Figure S7 shows the cross-sectional STEM image around the interface of SnSe film and MgO substrate. The clear layered atomic structure of SnSe phase was seen from the vicinity of the interface to bulk region, where the coherent interface between SnSe and MgO was formed, as indicated by vertical lines. Figure S8 summarizes the lattice parameters and lattice volume of SnSe films. With increase of Tg, the a-axis lattice parameter (a) decreased and c-axis lattice parameter (c) increased respectively, while the b-axis lattice parameter (b) was almost constant (Figs. S8(a-c)). As the result, the lattice volume (V) increased and became close to that of SnSe bulk2 at higher Tg. For SnSe epitaxial film on MgO substrate, the c was slightly smaller and a was larger than those of the film grown on glass substrate at same Tg = 500 oC. It is considered that the in-plane compressive strain along c-axis decreases c, while the expansion of a is caused by the epitaxial strain. Figure S9 shows the Tg dependence of Sn and Se atomic ratio in the SnSe films, where the Se/Sn ratio was almost constant at 1.00-1.01, regardless of the Tg change.     S6    Figure S2. XRD analysis of SnSe films deposited at Tg from RT to 500 oC on glass substrates. (a) Out-of-plane XRD patterns. (b) Rocking curves of 400 diffraction peaks. (c) In-plane XRD patterns. The diffraction indices of SnSe phase are described near the corresponding diffraction peaks in (a,c). Weak peaks marked by asterisks correspond to reflections from sample stage.   Figure S3. AFM images of SnSe films deposited on glass substrates at Tg = RT-500 oC.    S7   Figure S4. (a) Cross-sectional STEM image of SnSe film deposited on glass substrate at Tg = 500 oC. The arrows indicate the position of grain boundaries. (b) Atomic-scale STEM image of SnSe layer.     Figure S5. (a) Out-of-plane and (b) in-plane XRD patterns of SnSe film deposited on MgO (001) substrate at Tg = 500 oC.1 Rocking curve of 400 diffraction for SnSe phase is shown in the inset of (a). In-plane f scan of 002 diffraction for SnSe phase is shown in the inset of (b).       S8   Figure S6. AFM image of SnSe epitaxial film deposited on MgO (001) substrate at Tg = 500 oC.1   Figure S7. Cross-sectional STEM image of SnSe film deposited on MgO (001) substrate at Tg = 500 oC. The horizontal dotted line indicates the film/substrate interface position.     S9   Figure S8. (a-c) Lattice parameters for (a) a-axis, (b) b-axis, (c) c-axis, and (d) lattice volume (V) as a function of Tg for SnSe films on glass substrates. Those of SnSe epitaxial film with Tg = 500 oC are also shown for comparison. The dotted lines indicate the a, b, c and V of SnSe bulk.2    Figure S9. Atomic ratio of Sn and Se in SnSe films grown on glass substrates at different Tg = RT-500 oC. The plots indicate the average values from 15 measurements by electron probe micro-analyzer (EPMA) and the error bars indicate the standard deviation.    S10  Carrier transport analysis Arrhenius plots of n using ln #𝑛𝑇!!"& = #− "##$& #$%& + ln *+&%&&%!/(,  for the free electron apporximation are shown in Fig. S10(a), where Ea is the activation energy, nv the effective density of states (DOS) of the valence band, and nA the acceptor state density, respectively. The linear trend was observed in whole T range. The estimated Ea of n increased from 0.150 eV to 0.196 eV with increasing Tg from RT to 500 oC (Fig. S10(b)), indicating the shallower acceptor level in SnSe films grown at lower Tg. The high nA ~2.1×1020 cm-3 was observed for SnSe film at Tg = RT, but it decreased to 7.1×1019 cm-3 with increasing Tg to 500 oC (Fig. S10(c)). On the other hand, the SnSe epitaxial film exhibited slightly lower Ea = 0.186 eV but lower nA = 2.9×1019 cm-3.   In order to know the electronic structure change of SnSe films with different Tg, the optical absorption and hard X-ray photoemission spectroscopy (HAXPES) measurements were performed for SnSe films grown at Tg = RT and 400 oC on glass substrates. Optical bandgap (Eg) was evaluated by measuring transmittance (T) and reflectance (R) spectra, where the optical absorption coefficient (a) was estimated by the relationship a = loge[(1-R)/T]/d. The HAXPES measurement was performed at the BL15XU undulator beamline (the excitation x-ray energy: hv = 5953.4 eV) of SPring-8 at RT. The binding energy was calibrated with the Fermi level (EF) of an evaporated Au thin film, and the total energy resolution was set to 240 meV. The estimated Eg were almost similar at 0.94-0.96 eV (Fig. S11(a)). Meanwhile, the energies of valence band maximum (EVBM), determined by extrapolating the leading edge shown by the black dotted lines, were located at 0.14 eV from EF for Tg = RT and 0.20 eV for Tg = 400 oC, indicating that the EVBM shifted to a deeper energy by increasing the Tg (Fig. S11(b)). We constructed band alignment from the measured Eg and the EVBM (Fig. S11(c)). EF located near the VBM and the EF position moved away from the VBM due to the decrease of n with increasing the Tg. The increase of n can be explained by the increase of Sn vacancy (VSn) in SnSe films with decreasing  S11  Tg. We investigated the structure change by using the 1×3×3 supercell with 1 VSn or 1 Se vacancy (VSe) in SnSe with 72 atoms. The relaxed crystal structure is shown in Fig. S12(a). The VSn formation relaxed the strain in the Sn-Se molecular layers along the c-axis, resulting in the decrease of c, while a increase (Fig. S12(b)), which is consistent with the experimental results (Fig. S8). The small amount of naturally formed VSn in SnSe films would work as shallow acceptors for p-type conduction. Larger amount of VSn was formed at low Tg condition, but it was suppressed by increasing Tg, resulting in the decrease of n.    Figure S10. (a) Arrhenius plots of carrier concentration (n) for SnSe films. (b,c) Tg dependence of (b) activation energies (Ea) and (c) acceptor state density (nA).   Figure S11. (a) (ahn)1/2 plots for SnSe films grown on glass substrates at Tg = RT and 400 oC to estimate the in-direct gaps (Eg). The arrow indicates the band gap position. (b) HAXPES  S12  spectra near VBM. The energy of the VBM (EVBM) is estimated by the leading-edge analysis, as indicated by dotted black lines. (c) Schematic electronic structure. The energy of conduction band minimum (ECBM) and EVBM are indicated by red and blue lines, respectively. The acceptor level (EA), estimated from the Arrhenius plots of n (Fig. S10(b)), are also drawn by green lines.   Figure S12. Relaxed structures of 72-atom supercell SnSe models with (a) 1 Sn vacancy (VSn) and (b) 1 Se vacancy (VSe). The VSn or VSe concentration is 2.8%. (b) Comparison of lattice parameters (a,b,c) and volumes (V) for perfect SnSe model excluding vacancies and SnSe models involving VSn and VSe.    S13  References (1) He, X.; Chen, J.; Katase, T.; Minohara, M.; Ide, K.; Hiramatsu, H.; Kumigashira, H.; Hosono, H.; Kamiya, T. High-Mobility Metastable Rock-Salt Type (Sn,Ca)Se Thin Film Stabilized by Direct Epitaxial Growth on a YSZ (111) Single-Crystal Substrate. ACS Appl. Mater. Interfaces 2022, 14, 18682-18689. (2) Wu, P.; Ishikawa, Y.; Hagihala, M.; Lee, S.; Peng, K.; Wang, G.; Torii, S.; Kamiyama, T. Crystal structure of high-performance thermoelectric materials by high resolution neutron powder diffraction. Physica B: Condens. Mater. 2018, 551, 64-68.