Oxidation of silicon nanowire can transport much more light into silicon substrate

Silicon nanowire (SiNW) has been widely used for light-trapping in photovoltaics, optical sensors, and other optoelectronic devices. However, we found that 58.4% of the light trapped by a SiNW with a diameter of 60 nm and a length of 1 μm will be wasted: 64.5% of the trapped light will be absorbed within itself, and 90.5% of carriers excited by this part of light will recombine before being transported to the silicon substrate. In this work, it is shown that oxidation of SiNW can transport much more light into the silicon substrate. At first, our simulation results demonstrate that oxidation can dramatically reduce the percentage of absorbed light. In an oxidized SiNW (O-SiNW) with a total and silicon core diameter of 60 nm and 30 nm, respectively, the percentage is about 44.5%. Next, a low carrier recombination ratio, about 27.3%, can be obtained in O-SiNW due to the passivation effect of the oxide layer. As a result, oxidation of SiNW can reduce the proportion of wasted light from 58.4% to 12.1%. More importantly, oxidation almost doesn't sacrifice the light-trapping ability: experimental measurements demonstrate that the average reflectance of an O-SiNW array is only slightly higher than that of a SiNW array, 3.9% vs. 3.0%. Such O-SiNW is promising to be used for low-loss light-trapping in specially designed photovoltaic devices.