Performance of Nanocrystal ZnO Thin-Film Schottky Contacts on Cu by Atomic Layer Deposition

To address a "number of emerging applications" it is advantageous to synthesize semiconductor material on top of metal contacts. This is among the first reports of ZnO grown on top of copper (Cu) to form a Schottky contact (SC). Electrical and analytical studies were performed on SCs with ultrathin ZnO films grown by atomic layer deposition (ALD) in this work. Similar thickness films of 30 nm nanocrystal ZnO were deposited by plasma-enhanced ALD (PEALD) and thermal ALD (TALD). Devices with PEALD-ZnO thin films exhibited Schottky rectification with a barrier height of 0.55 eV and an ideality factor of 2.7 with an on/off rectification ratio about 75. A resultant avalanche breakdown strength of>2.4 MV/cm was achieved for PEALD-ZnO thin film. This is one of the highest reported values experimentally observed in ZnO. In contrast, devices with TALD-ZnO thin films demonstrated linear current-voltage characteristics. The PEALD-ZnO/Cu interface was characterized with glancing angel x- ray diffraction and an x-ray photoelectron spectrometer, demonstrating negligible oxidation on the Cu surface. This paper suggests that ametallic Cu bond to theZnOthin film is critical for demonstrating a rectifying Schottky contact.