Infrared optical characterization of doped ZnO nanorods

D.L. GAU; M. BERRUET; S. BOTASINI; E.A. DALCHIELE; R.E. MAROTTI

Workshop; XVII Giambiagi Winter School; 2015

Physics Department of Exact and Natural Sciences School of the University of Buenos Aires

ZnO is a transparent n-type semiconductor with a bandgap of approximately 3.3 eV and a refraction index of about 2. It is usually doped using group-III elements Al, In or Ga as substitutional elements for Zn and group-VII elements Cl and I as substitutional elements for O. Using appropriate methods it is possible to obtain ZnO nanorods (aspect ratio from 3-5). These structures are currently studied due to their applications in energy harvesting and light emitting devices. In the present work ZnO nanorods were grown electrochemically on a FTO substrate and doped using NH4Cl as Cl precursor. Such chloride impurities may act as electrical donors, producing an increase of free electrons. This behavior has been optically analyzed using infrared radiation. To perform the characterization the optical reflectance R(l) was measured in the band from 1.3 μm to 25 μm using a Shimadzu IR Prestige-21 Fourier Transform Infrared Spectrometer equipped with an SRM-8000A accessory. In the region from 1000 to 3600 nm the transmittance was measured using monochromated light (Oriel 77250 monochromator) and a Sciencetech IA-020-TE2-H InAs thermoelectrically cooled detector. From the results a metallic like behavior is observed: the reflectance increase to the IR and diminish into the visible region. In this region (transparency region) the behavior is complicated by oscillations associated with interference phenomena. The onset of reflectance shifts to the visible region when the concentration of Cl is increased,which implies that Cl is effectively generating free carriers in the semiconductor.