Browsing by Author "Samwel, Benard"

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    Effects of target composition and deposition parameters on the optical constants (n, k) of dc sputtered ZnO:al thin films
    (University of Dar es Salaam, 2013) Samwel, Benard
    Aluminium doped zinc oxide (ZnO:Al) is one of the most promising material as a transparent conductive electrode in solar cells with high visible transparency and high reflectance in the near infrared wavelength range along with good electrical conductivity. This research investigated the effects of target composition and deposition parameters on optical constants of DC magnetron sputtered ZnO:Al films. In this study, ZnO:Al thin films were deposited from ZnO:Al ceramic and Zn:Al metal alloy targets. The films’ UV/VIS/NIR transmittance and reflectance were determined using a spectrophotometer. Electrical sheet resistance of the films were obtained using a two-point probe. The refractive index n and extinction coefficient k were obtained from measured transmittance and reflectance spectral data using SCOUT 3 software. Spectral transmittance T for all films showed T > 83% at a wavelength (λ) of 550 nm with weighted luminous transmittance (Tlum) and solar transmittance (Tsol)of >80 and >79% respectively, with good NIR shielding. Band gap energies ranging from 3.20 to 3.56 and 3.24 to 3.67 eV for films prepared from ceramic and alloy targets, respectively, were obtained. Further addition of oxygen in films prepared from ceramic target resulted in poor film properties having high NIR transmittance and a decreased bang gap energy. The minimum electrical sheet resistance of 10 Ω/□ and 32 Ω/□ were obtained using alloy target and ceramic target, respectively. Generally, the calculated n and k in the visible part of the solar spectrum for different samples, ranged from 1.59 to 2.2 and 0.00013 to 1.2194 respectively, which are in agreement with the results of ZnO:Al thin films calculated using other methods.