High brightness InP micropillars grown on silicon with Fermi-level splits larger than 1 eV

The synthesis of III-V nanowires on silicon substrates is promising for reducing the manufacturing and balance-of-systems costs of III-V based photovoltaics. However, performances of III-V nanowire based solar cells have not yet been close to their bulk counterparts as nanostructures are fundamentally challenged by enhanced non-radiative losses due to their large surface-to-volume ratios, resulting in significantly reduced external fluorescence yields for spontaneous emission and therewith serious penalties in the open-circuit voltage. In this work, we report characteristics of micron-sized, single-crystalline, Wurzite-phased InP crystals directly grown on silicon substrates for photovoltaics applications. We found that under illumination intensities equivalent to 1 sun Fermi level splits can reach 0.89 eV in undoped InP pillars, 0.53 eV below the bandgap of wurtzite InP material at 1.42 e V. The brightness of pillars can be improved by doping the pillars which boosts radiative recombination rates inside the material and increases the brightness by more than an order of magnitude. In n-doped pillars, whose absorption edge is shifted to 1.49 eV due to the Burstein-Moss effect, Fermi-level splits larger than 1 eV are found, 0.46 eV below the absorption edge. Long non-radiative carrier lifetimes of 6.9 ns at room temprature further attest to the quality of the pillars. These results confirm that InP is a promising materials choice for photovoltaic devices in which the light absorber exhibits large surface-to-volume ratios.