Comparison of C doping technique between SiC and C targets for high-photoresponsivity BaSi₂ films by radio-frequency sputtering

Abstract

High-photoresponsivity BaSi2 films is of great importance for solar cell applications. The photoresponsivity was enhanced greatly in C-doped BaSi2 films formed by sputtering BaSi2 and SiC or C targets. The shift of Raman peak and optical absorption edge with increasing C concentration (n C) showed that more C atoms were incorporated in BaSi2 films when the SiC target was sputtered. When n C was 6 × 1020 cm−3 by the SiC target, the photoresponsivity approached 2 A W−1 under a bias voltage of 0.1 V between the top and bottom electrodes. This is the highest value ever reported for BaSi2 films.

Recent Progress Toward Realization of High‐Efficiency BaSi2 Solar Cells: Thin‐Film Deposition Techniques and Passivation of Defects

“…Figure 15a,b shows the Raman and photoresponse spectra of C-doped BaSi 2 films sputtered at 600 C on Si(111) at P ¼ 0.5 Pa and P BaSi2 ¼ 30 W, respectively. [57] The RF power on the SiC target (P SiC ) was varied in the range 0À200 W. Raman peaks from the Si tetrahedra in BaSi 2 , which are labeled A g , F g , and E g , were observed. The triangles (∇) indicate the vibrational modes originating from C atoms calculated by Quantum Espresso.…”

“…[15,94] However, handling of these elements is very difficult, Reproduced with permission. [57] Copyright 2020, Japan Society of Applied Physics. Schematics of vibrational modes of Si tetrahedra with a C atom positioned c) at a Si substitutional site and d) at an interstitial 4c site.…”

“…In addition, novel device structures have been proposed, [40][41][42][43][44][45][46][47][48][49][50] and passivation of defects in BaSi 2 has been demonstrated by atomic-hydrogen (H) [51][52][53][54][55][56] and carbon (C) doping. [27,30,57] For deposition techniques, vacuum evaporation of BaSi 2 granules [21][22][23][24][25] and sputtering of BaSi 2 targets [26][27][28][29][30] or cosputtering of Si and Ba targets [31] are suitable to form BaSi 2 films for large-scale deployment on inexpensive substrates like SiO 2 . Large minority-carrier lifetimes (>4 μs) have been obtained for polycrystalline BaSi 2 films by these methods, [27,58] and they are comparable with those of BaSi 2 epitaxial films obtained by molecular beam epitaxy (MBE), [52] showing the superiority of these deposition techniques.…”

“…Figure 15. a) Raman spectra of undoped and C-doped BaSi 2 films with P SiC of 30, 70, 150, and 200 W. Triangles (▾) indicate the vibrational modes originating from C atoms in the BaSi 2 lattice calculated by Quantum Espresso. b) Photoresponse spectra of undoped and C-doped BaSi 2 films at V bias ¼ 0.1 V. Reproduced with permission [57]. Copyright 2020, Japan Society of Applied Physics.…”

Zn1–xGexOy Passivating Interlayers for BaSi2 Thin-Film Solar Cells

“…Therefore, BaSi 2 is a promising material for terawatt-class power generation. The optical properties of BaSi 2 light absorber layers were significantly improved via hydrogen passivation, − post-annealing, light doping of impurities, − three-step growth, , and proper Ba-to-Si deposition rate ratios ( R Ba / R Si ) to achieve stoichiometry. , BaSi 2 has a small lattice mismatch with Si(111) (i.e., 0.1 and 1.1% along the b - and c -axes, respectively), allowing epitaxial growth on an inexpensive Si substrate . We demonstrated the operation of p-BaSi 2 /n-Si heterostructure solar cells with η ≈ 10% on n-Si substrates, , where most of the photons are absorbed in the n-Si substrates.…”