Structural and electrical characterization of rectifying behavior in n-type/intrinsic ZnO-based homojunctions

Yilmaz S., POLAT İ., Altindal S., BACAKSIZ E.

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, vol.177, no.8, pp.588-593, 2012 (SCI-Expanded) identifier identifier


ZnO nanorods were synthesized on n-Si substrates by a chemical bath deposition method. X-ray diffraction and scanning electron microscopy results showed that the deposited ZnO nanorods crystallize in the wurtzite structure and are highly textured with their c-axes normal to the substrate and show a clearly hexagonal morphology. A heavily compensated, intrinsic ZnO layer (i-ZnO) doped with both Mg and Na was deposited on the nominally undoped ZnO nanorods (which show a natural n-type behavior) to produce an i-ZnO/n-ZnO homojunction. The i-ZnO layer consisted of hexagonal shaped crystallites oriented mainly perpendicular to the substrate surface. The current-voltage (I-V) characteristics of these structures in the temperature range of 100-300K have been analyzed in the framework of standard thermionic emission (TE) theory with the assumption of a Gaussian distribution of the barrier heights. The values of zero-bias barrier height ((phi(bo),) and ideality factor (n) were found to be strongly temperature dependent whereby n decreases while phi(bo) increases with increasing temperature. A Richardson plot of our data shows straight line behavior and the values of activation energy (E-a = phi(bo)) and the Richardson constant (A*) determined from the intercept and slope of the plot were 0.770 eV and 2.61 x 10(-8) A cm(-2) K-2, respectively. The value of A* is much lower than the known value of 32 A cm(-2) K-2 for ZnO. Thus, a modified Richardson plot based on a Gaussian distribution of barrier heights was used which yields a mean barrier height ((phi) over bar (bo)) and modified effective Richardson (A**) of 0.782 eV and 39.09 A cm(-2) K-2, respectively. This value of A** is much closer to the theoretical value of 32 A cm(-2) K-2 for ZnO. (C) 2012 Elsevier B.V. All rights reserved.