Highly conductive thin films of ZnO have been prepared by conventional electron beam evaporation on glass substrates. The Al2O3 content of 0–5 wt% was added as dopant into ZnO to decrease resistivity of ZnO films. An Al-doped ZnO film with a resistivity of 1.0 × 10-3 Ωcm is obtained at a substrate temperature of 300°C with 1.0 wt% Al2O3 content; transmittance of this film is above 90% in the visible range with 100 nm thickness. The ZnO source material doped with Al2O3 is evaporated efficiently by a lower electron beam power compared to the case of nondoped ZnO. The c-axis orientation of ZnO films is facilitated by the addition of Al2O3 and the c-axis of Al-doped ZnO films is oriented perpendicular to glass substrates in the substrate temperature range of 60°C–350°C.
Aluminum-doped ZnO thin films were prepared by ionized deposition on glass substrates. The crystallinity and electrical properties of Al-doped ZnO films prepared by ionized evaporation depend on the deposition conditions. The c-lattice constant of ZnO films increases with ionization current and acceleration voltage. The spacing distribution of c-lattice planes varies inversely with the orientation distribution of the c axis, when deposition conditions such as ionization current, acceleration voltage, and substrate temperature are changed; the line width B002 of a (002) diffraction peak increases while the FWHM of rocking curve ΔΘ50 decreases. These changes of crystallographic characteristics cause a decrease in Hall mobility, and defects in the film resulting from ion bombardment cause a decrease in carrier concentration. Therefore, an increase in resistivity is observed in Al-doped ZnO films grown by ionized deposition. Ion bombardment during deposition must be minimized to avoid degradation of Al-doped ZnO films, because the properties of Al-doped ZnO films are significantly changed by ion bombardment of the film surface.
Heterojunction solar cells of Zn3P2/ITO have been fabricated by rf sputter depositing ITO films onto Zn3P2 multiple crystal, and their electrical and photovoltaic properties are studied. Multiple crystal boules of Zn3P2, 12–16 mm in diameter and 3 cm long with grain size of 1–5 mm in diameter, and resistivity ρ of 40–105 Ω-cm have been formed by vapor phase transport. The ρ of as-grown Zn3P2 has been reduced significantly by Ag doping above 400°C. A V
oc of 0.24–0.32 V and a J
sc of 13–26 mA/cm2 are measured and the power conversion efficiency of 1.1% is obtained without AR coating at simulated AM 1. The J-V characteristics suggest tunneling as the dominant conduction mechanism. A spectral response of J
sc shows a good band-pass behavior between 360 nm and 830 nm.
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