Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

Tsukahara, Daichi; Baba, Masakazu; Honda, Syuta; Imai, Yoji; Hara, Kosuke O.; Usami, Noritaka; Toko, Kaoru; Werner, J.H.; Suemasu, Takashi

doi:10.1063/1.4896760

Cited by 25 publications

(18 citation statements)

References 53 publications

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“…In the past, several impurity dopant candidates were attempted either to make an n‐type or a p‐type BaSi 2 thin film by using group 11 elements (Cu and Ag ), group 13 elements (B , Al , Ga , and In ), and group 15 elements (P , As , and Sb ). In line with the theoretical expectation , BaSi 2 films doped with group 13 elements except Ga exhibit n‐type conductivity, while those with Cu or group 15 elements exhibit p‐type conductivity. Table summarizes the carrier type and the maximum carrier concentrations at RT achieved by molecular beam epitaxy (MBE) or ion implantation into MBE‐grown BaSi 2 films.…”

Section: Introductionsupporting

confidence: 85%

“…Boron (B) was chosen as an impurity candidate in BaSi 2 to fabricate p‐type BaSi 2 epitaxial layers. Recently, after theoretical investigation of B‐doped BaSi 2 thin films, it was found that not only the Si substitution with B but also the interstitial insertion of B into the 4c site is energetically favorable . It was speculated that this difference comes from a smaller atomic radius of B than those of Sb‐, Al‐, and In‐atoms in BaSi 2 .…”

Section: Resultsmentioning

confidence: 99%

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Donor and acceptor levels in impurity-doped semiconducting BaSi₂ thin films for solar-cell application

Khan

Suemasu

2017

Phys. Status Solidi A

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Identification of donor and acceptor energy levels in BaSi 2 due to the suitable impurity injection of different types is very essential for the design and development of heterojunction or homojunction solar cells. In this article, donor and acceptor energy levels due to the impurity Sb-, In-, Ga-, Cu-, Al-, Ag-, P-, and B-doped BaSi 2 films grown by molecular beam epitaxy (MBE) were investigated. It was found that impurity Sb-, Ga-, Cu-, and P-doped BaSi 2 exhibited n-type conductivity, while impurity In-Al-, Ag-, and B-doped BaSi 2 exhibited p-type conductivity, using the Van der Pauw method at room temperature (RT). The temperature dependence of electron or hole concentrations indicated that the acceptor energy levels in impurity B-, In-, Ag-, and Al-doped BaSi 2 are 23, 86, 126, and 140 meV, respectively, and the donor energy levels in impurity Cu-, Sb-, P-, and Ga-doped BaSi 2 are 35, 47, 80, and 120 meV, respectively. The shallow acceptor level of 23 meV in p-type BaSi 2 due to B impurity atoms and two novel donor levels of 47 and 35 meV, respectively, due to Sb and Cu impurity atoms in n-type BaSi 2 were successfully identified for photovoltaic applications.

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Section: Introductionsupporting

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Donor and acceptor levels in impurity-doped semiconducting BaSi₂ thin films for solar-cell application

Khan

Suemasu

2017

Phys. Status Solidi A

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“…31,32 We have attributed the high L and pronounced photoresponsivity of undoped n-BaSi 2 on Si(111) to the downward band bending at the DBs, as determined by Kelvin probe force microscopy, which may restrict photogenerated minority carriers (holes) from the DBs. 33,34 In contrast, upward band bending is observed at the DBs in the case of BaSi 2 on Si(001), 33 meaning that the photogenerated minority carriers are directed toward defective DBs. Planview transmission electron microscopy (TEM) observations have shown that there are numerous defective DBs in BaSi 2 on Si(001), whereas many sharp straight DBs parallel to the (011) or (0-11) planes are found in BaSi 2 on Si(111).…”

Section: Introductionmentioning

confidence: 91%

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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“…Therefore, extensive studies have been conducted on GBs in solar cell materials, such as polycrystalline Si and chalcopyrite semiconductors in an attempt to improve efficiency. According to our previous investigations, 32,33 the electrostatic potentials were higher at GBs in undoped n-BaSi 2 and lightly Sb-doped n-BaSi 2 epitaxial films on Si(111) than those in the BaSi 2 grain interiors by approximately 10-30 mV. This downward band bending at the GBs is beneficial for n-type BaSi 2 , because the minority carriers (holes) are not attracted toward the GBs, which enable the suppression of minority-carrier recombination at the GBs.…”

Section: Introductionmentioning

confidence: 99%

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

Baba

Hara

Tsukahara

et al. 2014

Journal of Applied Physics

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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)

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Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

Abstract: Hard x-ray photoelectron spectroscopy study on valence band structure of semiconducting BaSi2

Cited by 25 publications

References 53 publications

Donor and acceptor levels in impurity-doped semiconducting BaSi₂ thin films for solar-cell application

Donor and acceptor levels in impurity-doped semiconducting BaSi₂ thin films for solar-cell application

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

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

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Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

Abstract: Hard x-ray photoelectron spectroscopy study on valence band structure of semiconducting BaSi2

Cited by 25 publications

References 53 publications

Donor and acceptor levels in impurity-doped semiconducting BaSi2 thin films for solar-cell application

Donor and acceptor levels in impurity-doped semiconducting BaSi2 thin films for solar-cell application

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

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

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Donor and acceptor levels in impurity-doped semiconducting BaSi₂ thin films for solar-cell application

Donor and acceptor levels in impurity-doped semiconducting BaSi₂ thin films for solar-cell application