Abstract: Addition of highly electronegative Nitrogen to Indium Antimonide substantially reduces its band gap. Theoretically, it is expected that one percent of nitrogen should reduce the band gap by about 100meV. Thus by reduction in the bandgap, the resulting material will be suitable for ‘far infrared’ detection. Three bulk crystals of InSb:N were grown by vertical directional solidification technique. The grown ingots were found detached from the ampoule wall. The physical properties and microstructures are studied. The smooth appearance of the crystal, uniform diameter across the length and other studies confirm the excellent quality of the crystal. Wavelength dispersive spectroscopy (WDS) was carried out for compositional analysis. The analysis confirmed the successful incorporation of nitrogen in the compound. The graph of absorption vs. energy was plotted to study shift in energy band gap. The deviation in the shift to the smaller wavelength is attributed to high (~1018/cm3) carrier concentration. The corresponding Moss-Burstein shift in the energy gap is calculated. The calculated values of the energy band shift due to all effects are summed up and compared with the observed value.