Bulk Photovoltaic Effect in Single Domain Ferroelectric SnS

Ferroelectrics are a group of materials in which spontaneous polarization reversal is possible in crystals with non-centrosymmetry, and ferroelectric domains have been subject to control in many electrical/mechanical conversion devices. On the other hand, oxide ferroelectrics exhibit the photovoltaic phenomenon known as the bulk photovoltaic effect (BPVE). BPVE is classified into two types: shift current, arising from non-centrosymmetric crystals, and the domain wall photovoltaic effect (DW-PVE), originating at the ferroelectric domain interface. BPVE is attracting attention as a next-generation photovoltaic mechanism capable of achieving the photovoltage above the band gap using a single material unlike pn junctions.<br/>Recently studies have intensively explored BPVE in 2D materials. However, there has been limited discussion on DW-PVE in 2D materials because research on ferroelectric 2D is limited. In this study, we have successfully grown sizable crystals of 2D ferroelectric SnS, facilitating comprehensive yet intricate examination of domain configurations utilizing polarized optical microscopy, second harmonic generation microscopy and piezoresponse force microscopy. By properly selecting the large ferroelectric single domain within SnS crystals, uniform intrinsic BPVE across the domain was conclusively demonstrated. Furthermore, to further enhance intrinsic BPVE, manipulation of strain poling increased photocurrent, suggesting that locally distributed polarizations due to imperfection introduced in SnS crystals are aligned by strain. These findings pave the way for a more profound understanding of DW-PVE in 2D ferroelectrics.