Figure 4. Leaky mode engineering in heterostructures.

(a) Schematic illustration for the refractive index profile in homogeneous and various heterogeneous structures. (b–d) The eigen magnetic field distribution of one leaky mode (TE₃₁) in a solid semiconductor NW in radius of 140 nm, a core-shell NW consisted of a 130 nm radius dielectric core and a10 nm thick semiconductor coating, and a core-multishell NW consisted of a 130 nm radius core, a10 nm thick semiconductor layer, and other three shell layers in thickness of 60 nm, 50 nm, and 60 nm from the inner to outer, respectively. The refractive indexes of the semiconductor and the dielectric core are set to be 4 and 2, respectively. Those of the three shell layers are set to be 2.7, 2.0, and 1.5 from the inner to outer. (e) Calculated spectral solar absorption for the three structures with the semiconductor materials being a-Si.