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(T) = 3.724-9.97 × 10^-4/(861+ T) eV. The plasma frequency and the free-carrier density of the GaN nanowires, deduced from the infrared reflectance minima, are estimated to be ω_p=1100±120cm^-1 and n_f = 3.73 × 10¹⁷cm^-3, respectively. Obtaining the free-carrier density from the infrared reflectance spectra is especially useful in research on nanostructured semiconductors.