Calnan, S.; Riedel, W.; Gledhill, S.; Stannowski, B.; Lux-Steiner, M.Ch.; Schlatmann, R.: Comparison of the influence of boron and aluminium doping on the material properties of electrochemically deposited ZnO films. Thin Solid Films 594 (2015), p. 215-224
10.1016/j.tsf.2015.05.051
Abstract:
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 peakwasmuchweaker for ZnO:Al and diminishedwith 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.