Effect of grain areas on minority-carrier lifetime in undoped n-type BaSi<sub>2</sub>on Si(111)

Takabe, Ryota; Hara, Kosuke, O.,; Baba, Masakazu; Wei, Du; Shimada, Noritomo; Toko, Kaoru; Usami, Noritaka; Suemasu, Takashi

doi:10.7567/jjapcp.3.011401

Cited by 6 publications

(8 citation statements)

References 9 publications

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“…36) In our previous studies, we found that the minority-carrier lifetime of BaSi2 was reproducibly improved by depositing an a-Si capping layer. 37) Besides, the potential barrier height of a-Si for photogenerated holes in n-BaSi2 was found to be 0.2 eV, 38) whereas that of native oxide was 3.9 eV. 39) Smooth extraction of photogenerated carriers through the a-Si capping layer was proved previously.…”

Section: Experimental Methodsmentioning

confidence: 70%

Growth of BaSi₂ continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi₂/n-Ge heterojunction solar cells

Takabe

Yachi

Tsukahara

et al. 2017

Jpn. J. Appl. Phys.

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We grew BaSi2 films on Ge(111) substrates by various growth methods based on molecular beam epitaxy (MBE). First, we attempted to form BaSi2 films directly on Ge(111) by MBE without templates. We next formed BaSi2 films using BaGe2 templates as commonly used for MBE growth of BaSi2 on Si substrates. Contrary to our prediction, the lateral growth of BaSi2 was not promoted by these two methods; BaSi2 formed not into a continuous film but into islands. Although streaky patterns of reflection high-energy electron diffraction were observed inside the growth chamber, no X-ray diffraction lines of BaSi2 were observed in samples taken out from the growth chamber. Such BaSi2 islands were easily to get oxidized. We finally attempted to form a continuous BaSi2 template layer on Ge(111) by solid phase epitaxy, that is, the deposition of amorphous Ba–Si layers onto MBE-grown BaSi2 epitaxial islands, followed by post annealing. We achieved the formation of an approximately 5-nm-thick BaSi2 continuous layer by this method. Using this BaSi2 layer as a template, we succeeded in forming a-axis-oriented 520-nm-thick BaSi2 epitaxial films on Ge substrates, although (111)-oriented Si grains were included in the grown layer. We next formed a B-doped p-BaSi2(20 nm)/n-Ge(111) heterojunction solar cell. A wide-spectrum response from 400 to 2000 nm was achieved. At an external bias voltage of 1 V, the external quantum efficiency reached as high as 60%, demonstrating the great potential of BaSi2/Ge combination. However, the efficiency of a solar cell under AM1.5 illumination was quite low (0.1%). The origin of such a low efficiency was examined.

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Section: Experimental Methodsmentioning

confidence: 70%

Growth of BaSi₂ continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi₂/n-Ge heterojunction solar cells

Takabe

Yachi

Tsukahara

et al. 2017

Jpn. J. Appl. Phys.

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“…Both theoretical and experimental studies have revealed that it has a band gap of approximately 1.3 eV [10,16,17] and has high absorption coefficients (α) exceeding 3 × 10 4 cm −1 for photon energies higher than 1.5 eV [17]. Recent experimental results demonstrating a large minority-carrier diffusion length (L 10 μm) [18,19], a long minority-carrier lifetime (τ 10 μs) [20][21][22], and potential variations across grain boundaries (GBs) [23] in BaSi2 confirm that this material is a new candidate for thin-film solar cells. The obtained values of α, L, and τ (described later) are sufficiently large for thin-film solar cell applications.…”

Section: Hybridized Orbitals and Connects With Three Othermentioning

confidence: 99%

“…Therefore, a defective surface deteriorates solar cell performance. μ-PCD measurements showed that τ reaches approximately 10 μs with excellent repeatability for n-BaSi2 by means of capping the BaSi2 surface with the native oxide or a few nanometers thick a-Si layer [77]. Note that we did not incorporate hydrogen atoms in the a-Si layers because we did not have such equipment.…”

Section: Surface Passivationmentioning

confidence: 99%

Exploring the potential of semiconducting BaSi₂for thin-film solar cell applications

Suemasu

Usami

2016

J. Phys. D: Appl. Phys.

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114

106

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Semiconducting barium disilicide (BaSi2), which is composed of earth-abundant elements, has attractive features for thin-film solar cell applications; both a large absorption coefficient comparable to copper indium gallium diselenide and a minority-carrier diffusion length much larger than the grain size of BaSi2 can be used to improve solar cells properties. In this review article, we explore the potential of semiconducting BaSi2 films for thin-film solar cell applications. We start by describing its crystal and energy band structure, followed by discussing thin-film growth techniques and the optical and electrical properties of BaSi2 films. We used a first-principle calculation based on density-functional theory to calculate the position of the Fermi level to predict the carrier type of impurity-doped BaSi2 films using either a Group 13 or 15 element, and compare the calculated results with the experimental ones. Special attention was paid to the minority-carrier properties, such as minority-carrier lifetime, minority-carrier diffusion length, and surface passivation. The potential variations across the grain boundaries measured by Kelvin-probe force microscopy allowed us to detect a larger minority-carrier diffusion length in BaSi2 on Si(111) compared with in BaSi2 on Si(001). Finally, we demonstrate the operation of p-BaSi2/n-Si heterojunction solar cells and discuss prospects for future development.

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“…10 Furthermore, BaSi2 has a sufficiently large minority-carrier diffusion length (L ≈ 10 μm) and a large minority-carrier lifetime ( ~ 10 s). [11][12][13][14][15] Based on its bipolar doping properties, [16][17][18][19] we have achieved conversion efficiencies (η) approaching 10% in p-BaSi2/n-Si heterojunction solar cells [20][21][22] and have recently demonstrated the operation of homojunction solar cells. 23,24 To achieve higher  in BaSi2-pn homojunction solar cells, the fabrication of high-quality BaSi2 light absorbing layers is urgently required.…”

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confidence: 99%

Investigation of native defects in BaSi₂ epitaxial films by electron paramagnetic resonance

Sato

Lombard

Yamashita

et al. 2019

Appl. Phys. Express

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We investigated photoresponse, photoluminescence (PL), and electron paramagnetic resonance (EPR) spectra of 0.5 m-thick BaSi2 films grown by molecular beam epitaxy using various Bato-Si deposition rate ratios (RBa/RSi). BaSi2 films (RBa/RSi = 2.2) showed the highest photoresponsivity at room temperature. In contrast, BaSi2 films with RBa/RSi away from 2.2 showed low photoresponsivity but intense sub-bandgap PL at 9 K. An anisotropic EPR line was observed below 20 K for such BaSi2 films. The EPR line disappeared for BaSi2 films passivated with atomic hydrogen. Thereby, the PL and EPR signals are interpreted to originate from native defects in the BaSi2 films.

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Effect of grain areas on minority-carrier lifetime in undoped n-type BaSi₂on Si(111)

Cited by 6 publications

References 9 publications

Growth of BaSi₂ continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi₂/n-Ge heterojunction solar cells

Growth of BaSi₂ continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi₂/n-Ge heterojunction solar cells

Exploring the potential of semiconducting BaSi₂for thin-film solar cell applications

Investigation of native defects in BaSi₂ epitaxial films by electron paramagnetic resonance

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Effect of grain areas on minority-carrier lifetime in undoped n-type BaSi2on Si(111)

Cited by 6 publications

References 9 publications

Growth of BaSi2 continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi2/n-Ge heterojunction solar cells

Growth of BaSi2 continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi2/n-Ge heterojunction solar cells

Exploring the potential of semiconducting BaSi2for thin-film solar cell applications

Investigation of native defects in BaSi2 epitaxial films by electron paramagnetic resonance

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Effect of grain areas on minority-carrier lifetime in undoped n-type BaSi₂on Si(111)

Growth of BaSi₂ continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi₂/n-Ge heterojunction solar cells

Growth of BaSi₂ continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi₂/n-Ge heterojunction solar cells

Exploring the potential of semiconducting BaSi₂for thin-film solar cell applications

Investigation of native defects in BaSi₂ epitaxial films by electron paramagnetic resonance