<p>Undoped and tin-doped zinc oxide (Sn:ZnO) thin films (TFs) were grown by the ambient pressure chemical vapor deposition (APCVD). The effect of different Sn concentration (0, 2, 4, and 6 at.%) on the optical behavior, structural composition, surface morphology, elemental composition, and electrical characteristics of the fabricated Al/n-Sn:ZnO/p-Si/Al heterojunction diodes were investigated. Changes in the physical attributes of the samples were studied using an ultraviolet–visible (UV–Vis) spectrophotometer, X-ray diffraction (XRD) technique, a field emission scanning electron microscope (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Current–voltage (I–V) characteristics of the Al/n-Sn:ZnO/p-Si/Al heterojunction diodes were also measured. Optical spectra analysis disclosed that the grown ZnO TFs possess low absorption and high transmittance in the visible-light range. Also, the optical energy gap (E_g) value of the films increased from 3.27 to 3.29 eV (shift toward the shorter-wavelength region) by changing Sn-doping concentration from 0 at.% to 6 at.%, respectively. XRD analysis demonstrated that all the grown films have a prominent intensity of the (002) peak at 34.51°, suggesting preferential growth along the <i>c</i>-axis. FESEM images revealed that the morphology of the films remarkably deteriorated with increasing Sn concentration. EDX findings indicated that the deposited films were doped with Sn without causing a large lattice strain. Electrical characteristics of the heterojunction diodes showed that the optimal Sn-doping of the ZnO films at 2 at.% produces a high-performance heterojunction diode with the lowest series resistance of 790 Ω, a minimal reverse saturation current of 2.46 nA, a near-unity ideality factor of 1.67, and an ideal rectification ratio of 26,831 at ±&#xa0;5 V, establishing it as the superior device configuration for optoelectronic applications.</p>