Drastic enhancement of photoresponsivity in C-doped BaSi₂ films formed by radio-frequency sputtering

Abstract

We formed carbon (C)-doped BaSi2 films by radio-frequency (RF) sputtering of BaSi2 and SiC targets simultaneously, and measured their optical properties. In the Raman spectra of BaSi2 films, peaks corresponding to vibrational modes of Si tetrahedra in the lattice of BaSi2 appear.On the other hand, in C-doped BaSi2 films, new peaks at around 260, 310, and 630 cm -1 other than those of BaSi2 films were observed. As the RF power of the SiC target (PSiC) increased, these intensities increased. The absorption edge of C-doped BaSi2 films was shifted to higher energies from 1.19 eV to 1.30 eV with increasing PSiC. We achieved the highest photoresponsivity of 1 A/W ever achieved for undoped BaSi2 films at a bias voltage of 0.1 V applied between the top and bottom electrodes. The marked enhancement of photoresponsivity was interpreted to originate from the increased carrier lifetime in C-doped BaSi2 films.

Fabrication of high-photoresponsivity BaSi2films formed on conductive layers by radio-frequency sputtering

“…This is because we need to set TS at 600 °C upon the formation of BaSi2 films by sputtering. [25][26][27] We see the change in color and aggregates on the surface of sample ITO- O atoms from the ITO underlayers. We ascribed this Raman line to substances such as Ba oxides 35) and Si gel.…”

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

“…[15,21] In this review, we focus on the recent progress of BaSi 2 to bridge the gap between the present status and that described in previous review articles. [14,15] Great progress has especially been made in thinfilm deposition techniques [22][23][24][25][26][27][28][29][30][31] and understanding the surface structure of BaSi 2 epitaxial films, [32] the reactions at the air/BaSi 2 and BaSi 2 /Si interfaces during post annealing, [33][34][35][36][37] and understanding the importance of satisfying the stoichiometry. [38,39] By positron annihilation spectroscopy, [39] it has been revealed that the electron concentration increases to %10 18 cm À3 with increasing vacancy-type defects [38] when the Ba/Si atomic ratio is far from the stoichiometric ratio.…”

“…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.…”

“…[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. In this review, we pay particular attention to sputtering techniques.…”

“…Amorphous Si (a-Si) and Al-O capping layers are effective to passivate the surface of BaSi 2 films. [61,62] For the bulk of BaSi 2 films, we discuss the effects of atomic-H [52] and C doping [27] on passivation of defects by experiments using photoresponsivity and minoritycarrier lifetime measurements together with discussion based on ab initio calculations. Although operation of BaSi 2 solar cells has been demonstrated in p-BaSi 2 /n-Si heterojunction solar cells with η close to 10% [63,64] and BaSi 2 homojunction solar cells (η % 0.28%), [65] the η achieved was much lower than expected.…”