Abstract
Ac dielectric measurements of Zn
1−
x
−
y
Fe
x
M
y
O samples with different M,
x
and
y
were made against frequency (
f
) up to 10 MHz. It is found that addition of Cu beside Fe in ZnO decreased the porosity and average size of grains, whereas they are increased by addition of Ni in place of Cu. The real and imaginary parts of dielectric constant (
ε
′,
ε
″) and dielectric loss (tan
δ
) are generally decreased by Fe, followed by an increase/decrease for (Fe + Ni)/(Fe + Cu) samples. Furthermore, the conduction is electronic below 10 kHz for all samples, but it is changed to hole as f increases above 10 kHz. Generally, the binding energy
W
m
, minimum hopping distance (
R
min
) and density of states at Fermi level N(
E
F
) are slightly increased by Fe, followed by a decrease for the co-doped samples. Interestingly, the N(
E
f
) of the Zn
0.9
Fe
.1
O (S2) sample is sharply increased with f, goes to optimum at 28.7 Hz and then decreases. In addition, the F-factor, for solar cell design, was increased by increasing f, and it has the samples order of (Fe), (Fe + Ni), (Zn) and (Fe + Cu). A single semicircle could be obtained from the Cole–Cole plot and the impedance of grain Z
\
(G) and that of grain boundaries Z
\
(GB) are increased by Fe, followed by an increase/decrease for (Fe + Cu)/(Fe + Ni) samples. The radius of arc increases for Fe and (Fe + Cu) samples, revealing a decrease in capacitance, while vice versa for (Fe + Ni) samples. The arcs seem to be centered below the Z
\
axis, indicating non-Debye relaxation of dipoles. These outcomes indicate that Fe and (Fe + Ni) samples shift the ZnO dielectric medium to higher values, and it is strongly recommended with Fe sample for solar cell design. In contrast, the (Fe + Cu) samples are recommended for high-frequency nonlinear optical devices due to their poor dielectric medium. To the best of our knowledge, the present systematic investigation may not be reported elsewhere.