Achieving near-unity broadband absorption in sparse arrays of GaAs NWs via a fundamental understanding of localized radial modes

We report a fundamental understanding of the mechanism for enhanced light absorption in sparse semiconductor nanowire arrays and design methods to achieve near-unity broadband absorption, demonstrated by GaAs nanowire arrays on a Si substrate. The sparse nanowire arrays absorb strongly into localized radial modes of individual nanowires, enabled by efficient scattering of incident light from neighboring nanowires. The radius-dependent localized modes led to two basic design approaches towards achieving near unity broadband absorption: (i) including multiple wire radii within an array for a 21% increase in absorbed current, and (ii) tapering the nanowires for a 23% increase in absorbed current.