Self-Assembled Growth of InN Microcages and Nanowires by Ammonolysis of an Amorphous Precursor and Their Optical Properties

Microcages and nanowires of InN were synthesized by ammonification of an indium precursor in the temperature range 650-700 degrees C. The phases of the ammonified products were identified through X-ray diffraction (XRD). Morphology and crystal structure of the samples were determined through field emission scanning electron microscopy (FESEM), transmission. electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) analysis. The thermal behavior of the precursor and synthesized InN powder was investigated using thermogravimetric analysis (TGA). The growth mechanism for the formation of different morphologies at various experimental conditions is explained on the basis of diffusion and vapor-solid process following least action principle. Large blue shift (1 - 1.5 eV) in the apparent band gap was observed with the increase of reaction time. The contributions of refractive index and the existence of three simultaneous direct transitions at 0.8, 1, 1.4 eV were identified from the optical absorption spectra. Electrical measurements were carried out to obtain a band gap of 1.25 eV in the sample.