Abstract:
Metal-Semiconductor junction studies play a very important role in discovering new
junction properties leading to improved electronic devices. Indeed, Schottky junction
is among the fundamental structures used in modern optoelectronics and microwave
devices. In this regard, low cost and eco-friendly metal-semiconductor devices with
inexpensive materials and fabrication techniques are extremely important. Among
other materials, p-Cu2O thin films grown by electrodeposition method have attracted
as potential candidates for developing Cu2O based low cost Schottky junction
devices. In this study, dependence of the p-Cu2O/Au junction properties on the pH
of the Cu2O film deposition bath has been investigated for the development of low
cost devices. p-Cu2O thin films were potentiostatically electrodeposited in a three
electrode electrochemical cell containing 3M lactic acid, 0.4M CuSO4 and NaOH at
different pH values. p-Cu2O/Au Schottky junctions were fabricated by sputtering Au
on masked Cu2O samples. Dark Capacitance – Voltage measurements (Mott-
Schottky plots) of the fabricated devices revealed that a positive shift of 620 mV of
the flat band potential against Au for the change in pH of the film deposition bath
from 7.0 to 13.0. This positive shift is significant when compared to the positive shift
of 350 mV at the p-Cu2O/electrolyte interface observed earlier. The interaction of
surface atoms with the electrolyte species at the Cu2O/electrolyte interface and the
presence of bare surface atoms at the Cu2O/Au interface might have led to this
improvement. The positive shift of the flat band potential manifests that the positive
shift in the valence band edge of p-Cu2O relative to the Fermi level of Au increases
the barrier height at the p-Cu2O/Au interface. Thus, the study reveals that the barrier
height at the p-Cu2O/Au interface can be controlled with the pH of the film deposition
both. As observed, dark Current-Voltage measurements on p-Cu2O/Au devices
resulted nearly ohmic behavior for low pH values and non ohmic diode behavior for
high pH values. This suggests that for high pH values of the film deposition bath of
p-Cu2O improved Schottky junctions can be in fabricated with Au, suitable for
various device applications such as rectifying circuits, photovoltaics, etc.
