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Two-junction-nanowire arrays (SnO₂ capped ZnO nanowire arrays on Zn substrate) are synthesized using a two-step-solution-reaction. The bare single crystalline ZnO nanowires give reasonably intense band edge luminescence but also strong green emission likely due to surface defects. The SnO₂ capping treatment not only introduces caps on the tip of the ZnO nanowires but also partially passivates the nanowire surfaces, leading to improved near band edge emission and the suppression of the defect luminescence. The nanowire array configuration allows a straight forward electrical measurement on the single nanowire junction (Zn−ZnO−SnO₂). The I−V results indicate that a little barrier exists in between the Zn substrate and the nanowire. The observation of more complicated electrical behaviors of the two-junction system (Zn/ZnO/SnO₂) discloses the nonuniform doping of the SnO₂ cap, which is consistent …