Optical characterization of wurtzite gallium nitride nanowires

The optical properties of the gallium nitride (GaN) nanowires are examined by the transmission method in the ultraviolet-visible range (1–5 eV) and by the reflection method in the infrared range (500–4000 cm⁻¹). The absorption edge of the GaN nanowires is blueshifted by 0.2 eV from the bulk edge. The temperature dependence of the energy gap is expressed by, $E_g{\text{(T)=3.724−9.97×10}}^{\text{−4}}\text{/(861+T)\hspace{0.05em}}\mathrm{eV}.$ The plasma frequency and the free-carrier density of the GaN nanowires, deduced from the infrared reflectance minima, are estimated to be ${\omega }_p\text{=1100±120\hspace{0.05em}}{\mathrm{cm}}^{\mathrm{-1}}$ and $n_f{\text{=3.73×10}}^{17} {\mathrm{cm}}^{\mathrm{-3}},$ respectively. Obtaining the free-carrier density from the infrared reflectance spectra is especially useful in research on nanostructured semiconductors.