Transparent conductive ZnO:Al films grown by atomic layer deposition for Si-wire-based solar cells

Structural, electrical, and optical properties of atomic layer-controlled Al-doped ZnO (ZnO:Al) films grown by atomic layer deposition (ALD) on glass substrates were characterized at various growth temperatures for use as transparent electrodes. The Al atomic content in ZnO:Al films increased due to the reduced ZnO film growth rate with increasing temperature. The preferred orientation of ZnO:Al films was changed, and the optimum condition for best crystallinity was identified by varying the growth temperature. Furthermore, the carrier concentration of free electron was increased by substituting the Zn sites with Al atoms in the crystal, resulting from monolayer growth based on alternate self-limiting surface chemical reactions. The electrical resistivity of ZnO:Al film grown by ALD at 225 °C reached the lowest value of 8.45 × 10−4 Ω cm, with a carrier mobility of 9.00 cm2 V−1 s−1 and optical transmittance of ∼93%. This result demonstrates that ZnO:Al films grown by ALD possess excellent potential for applications in electronic devices and displays as transparent electrodes and surface passivation layers.

► Monolayer growth enables increase in the carrier concentration of free electron.
► Electrical resistivity of the ZnO:Al film is improved with increasing ALD growth temperature.
► Optical bandgap energy of the ZnO:Al films shows a tendency to increase.
► ZnO:Al films grown by ALD possess excellent potential for the surface passivation layers.