Abstract:
Current–voltage (IV) and capacitance–voltage (CV) measurement techniques have successfully been
employed to study the effects of annealing highly rectifying Pd/ZnO Schottky contacts. IV results reveal
a decrease in the contact quality with increasing annealing temperature as confirmed by a decrease
in the zero bias barrier height and an increase in the reverse current measured at
−1.5 V. An average
barrier height of (0.77
±
0.02) eV has been calculated by assuming pure thermionic emission for the
as-deposited material and as (0.56
±
0.03) eV after annealing at 550 ◦C. The reverse current has been
measured as (2.10
±
0.01)
×
10−10 A for the as-deposited and increases by 5 orders of magnitude after
annealing at 550 ◦C to (1.56
±
0.01)
×
10−5 A. The depletion layer width measured at
−2.0 V has shown
a strong dependence on thermal annealing as it decreases from 1.09 m after annealing at 200 ◦C to
0.24 m after annealing at 500 ◦C, resulting in the modification of the dopant concentration within the
depletion region and hence the current flowing through the interface from pure thermionic emission to
thermionic field emission with the donor concentrations increasing from 6.90
×
1015 cm−3 at 200 ◦C to
6.06
×
1016 cm−3 after annealing at 550 ◦C. This increase in the volume concentration has been explained
as an effect of a conductive channel that shifts closer to the surface after sample annealing. The series
resistance has been observed to decrease with increase in annealing temperature. The Pd contacts have
shown high stability up to an annealing temperature of 250 ◦C as revealed by the IV and CV characteristics
after which the quality of the contacts deteriorates with increase in annealing temperature.
