Molecular monolayers for conformal, nanoscale doping of InP nanopillar photovoltaics

Semiconductor nanopillar arrays with radially doped junctions have been widely proposed as an attractive device architecture for cost effective and high efficiency solar cells. A challenge in the fabrication of three-dimensional nanopillar devices is the need for highly abrupt and conformal junctions along the radial axes. Here, a sulfur monolayer doping scheme is implemented to achieve conformal ultrashallow junctions with sub-10 nm depths and a high electrically active dopant concentration of 10¹⁹ - 10²⁰ cm^-3 in arrays of InP nanopillars. The enabled solar cells exhibit a respectable conversion efficiency of 8.1% and a short circuit current density of 25 mA/ cm³. The work demonstrates the utility of well-established surface chemistry for fabrication of nonplanar junctions for complex devices.