Disorder induced absorption enhancement of light in GaAs nanowire array

Light absorption characteristics of vertically aligned GaAs nanowire (NW) arrays with disordered diameters and heights are investigated in this work using finite difference time domain (FDTD) analysis technique. By varying the random height ranges, an optimum variation range of 1000-2000 nm is obtained that provides the maximum average absorbance at different fill-factors of the arrays. An array having random heights of the NWs within the optimized range is found to have better absorbance for both normal and oblique incidence of light compared to the uniform height structure. Even for 45 degrees incidence angle of light, average absorbance is obtained to be 2% higher for the random-height array, compared to the case of absorbance obtained for the uniform height structure. The proposed arrays having random diameters provide up to 12.8% improvement in short circuit current density whereas the random-height structure enhances the short circuit current density by 1.1% compared to the arrays having uniform diameter and height. The present work also provides an effective medium theory based theoretical model taking into account the random height variation of the arrays. The theoretically calculated values are found to be in good agreement with FDTD simulation results, thereby providing further guidelines for designing random array based high performance photonic devices.