Light Trapping in Coaxial Nanowires of c-Si Cores and a-Si Shells

Abstract

Light absorption is investigated in coaxial nanowires (NWs) of crystalline silicon (c-Si) cores and amorphous silicon (a-Si) shells, including both cases of single coaxial NWs and coaxial NW arrays, for an incident light spectrum of 1.0–4.0 eV covering the major solar band for photovoltaic cells. Based on the Lorenz-Mie light scattering theory for the single coaxial NWs and the rigorous coupled-wave analysis method for the coaxial NW arrays, it is found that the incident light is effectively trapped in the coaxial NWs through absorption resonances so that the light absorption of the coaxial NWs can be significantly enhanced compared to that of c-Si NWs. In the coaxial NWs, the absorption resonances occur due to their subwavelength dimensions, as in the c-Si NWs, whereas the absorption enhancement originates from the a-Si shells. By tuning their structural parameters, the light absorption in the coaxial NWs can be readily optimized for photovoltaic applications. At the optimal absorption conditions, the photocurrent in the coaxial NWs can be enhanced up to 560 % (single case) and 14 % (array case) compared to that in the c-Si NWs. The underlying physics of the light absorption in the coaxial NWs is discussed in terms of the excitation of leaky-mode resonances. The practical use of the coaxial NWs for photovoltaic cells is also addressed.