Potential variation around grain boundaries in BaSi2 films grown on multicrystalline silicon evaluated using Kelvin probe force microscopy

Abstract

Investigations on residual strains and the cathodoluminescence and electron beam induced current signal of grain boundaries in silicon J. Appl. Phys. 115, 163511 (2014) Potential variations across the grain boundaries (GBs) in a 100 nm thick undoped n-BaSi 2 film on a cast-grown multicrystalline Si (mc-Si) substrate are evaluated using Kelvin probe force microscopy (KFM). The h-2h X-ray diffraction pattern reveals diffraction peaks, such as (201), (301), (410), and (411) of BaSi 2 . Local-area electron backscatter diffraction reveals that the a-axis of BaSi 2 is tilted slightly from the surface normal, depending on the local crystal plane of the mc-Si. KFM measurements show that the potentials are not significantly disordered in the grown BaSi 2 , even around the GBs of mc-Si. The potentials are higher at GBs of BaSi 2 around Si GBs that are formed by grains with a Si(111) face and those with faces that deviate slightly from Si(111). Thus, downward band bending occurs at these BaSi 2 GBs. Minority carriers (holes) undergo a repelling force near the GBs, which may suppress recombination as in the case of undoped n-BaSi 2 epitaxial films on a single crystal Si (111)

Electronic properties of thin BaSi2 films with different orientations

“…2 indicating that all Si 4 tetrahedra are preserved at the surface as experimentally observed in Ref. 18 for the BaSi 2 (100). After full structural optimization the BaSi 2 (100) and (111) surfaces possess Ba atoms as topmost atoms while, on the contrary, Si atoms of complete Si 4 tetrahedra terminate the BaSi 2 (110) surface.…”

“…29) Our attempts to construct surfaces with broken tetrahedra having less Si atoms resulted in sizable increasing of surface energy. Thus, the experimental observation that the BaSi 2 (100) films are terminated by complete Si 4 tetrahedra 18) seems to be typical of any BaSi 2 surface. To this end we can link values of surface energy and charge transfer between atoms to a type of topmost atoms.…”

“…There is an experimental investigation of a surface structure of BaSi 2 films by using the coaxial impact-collision ion scattering spectroscopy and atomic force microscopy pointing out that BaSi 2 (100) films on a Si(111) substrate are terminated by Si 4 tetrahedra. 18) However, comprehensive knowledge of a BaSi 2 surface structure along with energy positions of surface states, which is still lacking, could help in optimizing a BaSi 2 =Si heterojunction in order to achieve better performance of BaSi 2 thin-film based solar cells.…”

Formation of BaSi2 heterojunction solar cells using transparent MoOx hole transport layers

“…20 Grain boundaries (GBs) in polycrystalline semiconductors often degrade their electrical and optical properties. However, Kelvin probe force microscopy measurements indicate that the band structure at BaSi 2 GBs leads to repulsion of the minority carriers, [21][22][23] which reduces the charge carrier recombination at GBs. This band bending at GBs contributes to a long minority-carrier diffusion length in BaSi 2 .…”

Recent advances in computational studies of thin-film solar cell material BaSi2

“…[20][21][22][23][24][25][26] This is because BaSi 2 has a suitable band gap in the range 1.1-1.3 eV, a large photo absorption coefficient of 10 4 cm −1 at 1.5 eV, high quantum efficiency (>70%), a long minority-carrier diffusion length (10 μm), and a long minority-carrier lifetime (10 μs). [27][28][29][30][31][32][33][34][35][36] In fact, a double-digit (∼10%) conversion efficiency has also been reported for the first prototype p-BaSi 2 /n-Si heterojunction solar cell. 37,38) Understanding fundamental properties such as absorption coefficient, band edge energies, band offsets, thermodynamic stability, and defect physics in the absorber material is crucial to designing an efficient thin-film solar cell.…”