Molecular Beam Epitaxy of BaSi<sub>2</sub> Films with Grain Size over 4 µm on Si(111)

Baba, Masakazu; Nakamura, Kotaro; Du, Weijie; Khan, M. Ajmal; Koike, Shintaro; Toko, Kaoru; Usami, Noritaka; Saito, Noriyuki; Yoshizawa, Noriko; Suemasu, Takashi

doi:10.1143/jjap.51.098003

Cited by 25 publications

(21 citation statements)

References 15 publications

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“…26 The domain size in BaSi 2 on Si(111) can be varied from 0.2 to 4.0 lm, while the domain size for BaSi 2 on Si(001) can vary from 1.0 to 9.0 lm. [27][28][29] With regard to domain size, therefore, the use of Si(001) is preferable because the number of domain boundaries (DBs) between the BaSi 2 epitaxial variants will decrease. However, L can be as low as 1.5 lm for undoped Published by AIP Publishing.…”

Section: Introductionmentioning

confidence: 99%

First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

Baba

Kohyama

Suemasu

2016

Journal of Applied Physics

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Epitaxial films of BaSi2 on Si(111) for solar cell applications possess three epitaxial variants and exhibit a minority carrier diffusion length (ca. 9.4 μm) much larger than the domain size (ca. 0.2 μm); thus, the domain boundaries (DBs) between the variants do not act as carrier recombination centers. In this work, transmission electron microscopy (TEM) was used to observe the atomic arrangements around the DBs in BaSi2 epitaxial films on Si(111), and the most stable atomic configuration was determined by first-principles calculations based on density functional theory to provide possible interface models. Bright-field TEM along the a-axis of BaSi2 revealed that each DB was a twin boundary between two different epitaxial variants, and that Ba(II) atoms form hexagons containing central Ba(I) atoms in both the bulk and DB regions. Four possible interface models containing Ba(I)-atom interface layers were constructed, each consistent with TEM observations and distinguished by the relationship between the Si tetrahedron arrays in the two domains adjacent across the interface. This study assessed the structural relaxation of initial interface models constructed from surface slabs terminated by Ba(I) atoms or from zigzag surface slabs terminated by Si tetrahedra and Ba(II) atoms. In these models, the interactions or relative positions between Si tetrahedra appear to dominate the relaxation behavior and DB energies. One of the four interface models whose relationship between first-neighboring Si tetrahedra across the interface was the same as that in the bulk was particularly stable, with a DB energy of 95 mJ/m2. There were no significant differences in the partial densities of states and band gaps between the bulk and DB regions, and it was therefore concluded that such DBs do not affect the minority carrier properties of BaSi2.

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Section: Introductionmentioning

confidence: 99%

First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

Baba

Kohyama

Suemasu

2016

Journal of Applied Physics

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“…An air-stable BaSi 2 source can be used without any pretreatment, while the MBE uses a reactive Ba source and the sputtering method requires compacting the powder to make a target. It should also be noted that the deposition rate (300 nm/min) of the evaporation method is considerably higher than sputtering (30 nm/min [9]) and MBE (2 nm/min [12]).…”

Section: Introductionmentioning

confidence: 99%

Structural and electrical characterizations of crack-free BaSi2 thin films fabricated by thermal evaporation

et al. 2015

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The BaSi 2 semiconductor is a promising candidate for an earth-abundant solar cell absorber. In this study, we have realized a crack-free BaSi 2 film by a simple thermal evaporation technique on a CaF 2 substrate at a growth temperature of 500 • C for electrical characterization. A Si layer preliminarily formed on the substrate by sputtering is a key to obtain stoichiometric BaSi 2 film. Detailed structural characterization of the evaporated films with different Si layer thicknesses by X-ray diffraction, scanning and transmission electron microscopy demonstrates that a crack-free 370-nm-thick BaSi 2 film is formed by consuming the Si layer. It is observed that the 90-nm-thick bottom part is microcrystalline and contains Ar atoms, which come from Si deposition atmosphere. The surface of the BaSi 2 layer is found to be covered by an amorphous Si layer due to Si-rich vapor at the last stage of evaporation. Electrical properties of the BaSi 2 film is revealed by Hall measurement and the electron density and mobility are found to be 6×10 20 cm −3 and 0.04 cm 2 /V·s, respectively. Owing to a better crystalline quality contributed by the preliminarily-deposited Si layer, minority-carrier lifetime of the evaporated film (0.6 µs) is twenty times longer than previous films on glass substrates.

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“…17 The grain size in BaSi 2 can be controlled from 0.1 to 4 lm, according to the growth conditions. 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.…”

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

Takabe

Baba

et al. 2015

Applied Physics Letters

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Heterojunction solar cells that consist of 15 nm thick molybdenum trioxide (MoOx, x < 3) as a hole transport layer and 600 nm thick unpassivated or passivated n-BaSi2 layers were demonstrated. Rectifying current-voltage characteristics were observed when the surface of BaSi2 was exposed to air. When the exposure time was decreased to 1 min, an open circuit voltage of 200 mV and a short circuit current density of 0.5 mA/cm2 were obtained under AM1.5 illumination. The photocurrent density under a reverse bias voltage of −1 V reached 25 mA/cm2, which demonstrates the significant potential of BaSi2 for solar cell applications.

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Molecular Beam Epitaxy of BaSi₂ Films with Grain Size over 4 µm on Si(111)

Cited by 25 publications

References 15 publications

First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

Structural and electrical characterizations of crack-free BaSi2 thin films fabricated by thermal evaporation

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

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Molecular Beam Epitaxy of BaSi2 Films with Grain Size over 4 µm on Si(111)

Cited by 25 publications

References 15 publications

First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

First-principles study of twin grain boundaries in epitaxial BaSi2 on Si(111)

Structural and electrical characterizations of crack-free BaSi2 thin films fabricated by thermal evaporation

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

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Molecular Beam Epitaxy of BaSi₂ Films with Grain Size over 4 µm on Si(111)