Comparison of the influence of boron and aluminium doping on the material properties of electrochemically deposited ZnO films

• Crystalline ZnO grown by electrochemical deposition.
• Comparison of influence of H3BO3 and Al(NO3)3 as dopant sources.
• Different ZnO crystalline orientation for Al and boron doping.
• Film surface chemical composition suppressed electrical conductivity.

The effect of varying the boron and aluminium content of the starting electrolyte for extrinsically doped ZnO films grown on SnO2:F substrates by electrochemical deposition was investigated. The ZnO:B film surface was characterized by grains with mainly hexagonal faces exposed while the exposed faces of the ZnO:Al grains were rectangular. Whereas a B3 +/Zn2 + ratio of up to 10 at.% in the electrolyte had no significant effect on the crystalline structure of the ZnO films, an Al3 +/Zn2 + ratio above 0.25 at.% increased the disorder in the crystalline structure. All the boron doped films exhibit a strong E2-high Raman mode related to wurtzite ZnO structure but this peak was much weaker for ZnO:Al and diminished with increasing Al incorporation in the films. Exposing the films to ultra-violet light reduced their effective sheet resistance from values beyond measurement range to values between 40 and 5000 kΩ/sq for film thicknesses of 200–550 nm. Inspection of the optical spectra near the bandgap edge and the plasma edge in the mid infrared range, showed that the Al-doping resulted in a higher carrier concentration ~ 1020 cm− 3 than B-doping. X-ray electron spectroscopy showed that the dopant efficiency was limited by the absence of dopant atoms near the surface of all the ZnO:B films and of the lightly doped ZnO:Al and, by the formation of aluminium oxide at the surface of the more highly doped ZnO:Al films.