Co-sputtering deposition of high-photoresponsivity and high-mobility polycrystalline BaSi2 films on Si substrates

Abstract

• Stoichiometric BaSi 2 films were obtained by co-sputtering from BaSi 2 and Ba targets. • Power applied on the targets controlled the Ba and Si species reaching the substrate. • Deposition without Ba target resulted in Ba-deficient films. • Large photoresponsivity was observed in spite of polycrystalline films. Barium disilicide (BaSi 2 ) has shown great promise for solar cell applications. Recent studies have revealed that defects such as Si vacancies in BaSi 2 films caused by the Ba/Si atomic ratios being away from stoichiometry degrade the electrical and photoresponse properties of BaSi 2 films. The formation of BaSi 2 films by sputtering has been performed using basically one BaSi 2 target, which makes it difficult to control the Ba/Si atomic ratio of the grown films. In this work, we investigate the formation of BaSi 2 films on Si(111) substrates by radio-frequency (RF) sputtering of BaSi 2 and Ba targets, and independently control the RF powers set on the targets. It is found that the contribution of sputtering the Ba target to the BaSi 2 growth rate ( GR Ba / GR BaSi2 ) can be used to find the growth conditions for high-photoresponsivity BaSi 2 films. The highest photoresponsivity reached 1.4 A W −1 at room temperature for BaSi 2 films grown at 600°C when a bias voltage of 0.5 V was applied between the front indium tin oxide electrodes and rear Al electrodes. The electron mobility depended on sputtering conditions, but mostly exceeded 1000 cm 2 V −1 s −1 in spite of randomly oriented polycrystalline films. These values are comparable to those obtained for BaSi 2 epitaxial films on Si(111) by molecular beam epitaxy.