Fabrication of III-nitride nanorods photovoltaic grown on silicon (111) by PA-MBE
Ching-Wen Chang1*, Hui-Chun Huang2, Niou-Jin Ho2, Fu-Peng Lu1, Li-Wei Tu1
1Department of Physics and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan
2Department of Materials and Opto-electronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan
* presenting author:張菁文, email:changchingwen0921262805@gmail.com
As the energy crisis is getting more serious and more attention, more researchers try to tap new resources and reduce costs. To resolve this, green energy research and development become increasingly important. Among them, light-emitter diode (LED) and solar cell industries are two vital sectors and develop rapidly. In the past, the group of III-nitrides has been successfully applied to LED devices and brings huge commercial success in the past few decades. Now, the research experience on III-nitrides is extended to the photovoltaic applications. There are many advantages of nitride materials on photovoltaic systems, such as a direct band gap with large absorption coefficient, a wide band-gap range covering most of the solar spectrum, high carrier mobility, and superior radiation resistance. However, the issues of impurities and non-radiative recombination centers increases because of the low-temperature InGaN thin film growth other than In clustering issue. These may lead to the decrease of carrier diffusion length and limitation of the solar cell energy conversion efficiency. Previously, Wierer Jr et al. demonstrated the III-nitride core-shell nanowire arrayed solar cells on sapphire with an energy conversion efficiency of ~0.3%, a short circuit current density of ~1 mA/cm2 and an open circuit voltage of 0.5 eV. Nevertheless, it still shows a lot of challenges and potential capabilities for high efficiency III-nitride photovoltaic devices.
In this study, the p-i-n III-nitride nanorods photovoltaic devices are fabricated successfully on low-cost silicon (111) substrate with plasma-assisted molecular beam epitaxy (PA-MBE) technique. The indium concentration is estimated to be about 11% by 2-theta scan of x-ray diffraction using Vegard’s law. The high resolution transmission electron microscopy (HR-TEM) images show the atomic images free from dislocations. The high-angle annular dark field (HAADF) image shows the composition distribution of InGaN nanorod. Solar cell devices are fabricated by photolithographic processes. J-V measurements are performed and an active area energy conversion efficiency of 1.12% under 1-sun AM1.5G illumination is obtained.

Keywords: Nanorod, Nitride, solar cells