Evaluation of potential variations around grain boundaries in BaSi2 epitaxial films by Kelvin probe force microscopy

Kohyama

Suemasu

2016

Self Cite

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.

Section: Introductionmentioning

confidence: 98%

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

Kohyama

Suemasu

2016

Self Cite

“…42 The value of n in the Sb-doped BaSi 2 films, samples S1-S3, was controlled by changing the substrate temperature, T S , as 580, 550, and 520 C, respectively, while the temperature of Sb crucible, T Sb , was fixed at 250 C. Undoped n-BaSi 2 (n ¼ 5 Â 10 15 cm À3 ) in Ref. 32, was used as sample S0 for comparison. The value of p in the B-doped BaSi 2 films, samples B1-B3, was controlled by varying the temperature of B crucible, T B , as 1300, 1400, and 1450 C, respectively, while T S was fixed at 650 C. The sample preparation is summarized in Table I.…”

Section: Methodsmentioning

confidence: 99%

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

Tsukahara

Honda

et al. 2014

“…0.2 lm). 9 In contrast, upward band bending occurs at the GBs in undoped n-BaSi 2 epitaxial films on Si(001), 32 which results in a smaller minority-carrier diffusion length (ca. 1.5 lm).…”

Section: Introductionmentioning

confidence: 99%

“…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

Hara

Tsukahara

et al. 2014

Self Cite

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)