Nano Research

Article Title

Impact of insulator layer thickness on the performance of metal–MgO–ZnO tunneling diodes


metal–insulator–semiconductor (MIS) diode, ZnO nanodevices, MgO layer, tunneling mechanism


The performance of metal–insulator–semiconductor (MIS) type tunneling diodesbased on ZnO nanostructures is investigated through modeling. The frameworkused in this work is the Schrödinger equation with an effective-mass approximation.The working mechanism of the MIS type tunneling diode is investigatedby examining the electron density, electric field, electrostatic potential, andconduction band edge of the device. We show that a valley in the electrostaticpotential is formed at the ZnO/MgO interface, which induces an energy barrierat the ZnO side of this interface. Therefore, electrons need to overcome twobarriers: the high and narrow MgO barrier, and the barrier from the depletionregion induced at the ZnO side of the ZnO/MgO interface. As the MgO layerbecomes thicker, the valley in electrostatic potential becomes deeper. At the sametime, the barrier induced at the ZnO/MgO interface becomes higher and wider.This leads to a fast decrease in the current passing through the MIS diode. Weoptimize the thickness of the MgO insulating layer, sandwiched between a ZnOfilm (in this work we use a single ZnO nanowire) and a metal contact, to achievemaximum performance of the diode, in terms of rectification ratio. An optimalMgO layer thickness of 1.5 nm is found to yield the highest rectification ratio,of approximately 169 times that of a conventional metal–semiconductor–metalSchottky diode. These simulated results can be useful in the design and optimizationof ZnO nanodevices, such as light emitting diodes and UV photodetectors.

Graphical Abstract


Tsinghua University Press