A study of band-bending and barrier height variation in thin film n-CdSe0.5Te0.5 photoanode/polysulphide junctions

Polycrystalline thin films of n-CdSe0.5Te0.5 were deposited in a vacuum of 5 x 10(-5) torr by thermal flash evaporation with a deposition rate of 20 +/- 1 Angstrom s(-1) on indium oxide coated glass plates [sigma=1.25 x 10(4)(Omega-cm)(-1)] held at a temperature of 473 K. The change in the pH value of the polysulphide electrolyte from 12.5 to 8.0 leads to a fall in the extent of band bending from 680 meV to 420 meV and decrease in the barrier height from 690 meV to 430 meV. The barrier heights as calculated from Mott-Schottky plots and current-voltage plots are compared. From the reverse saturation current (I-0) variation with temperature, it is found that the barrier height decreases from 690 meV to 430 meV with decrease in pH of the electrolyte from 12.5 to 8.0. The variation of diode ideality factor n, with temperature was also studied. It was found that the diode ideality factor n, decreases with increase of temperature, viz. from 3.00 to 2.00 with rise in temperature from 300 K to 333 K. This is due to the additional injection of electrons from the bulk into the junction region because of increase in temperature. Copyright (C) 1996 Elsevier Science Ltd.