Selective formation of Ohmic junctions and Schottky barriers with electrodeposited ZnO

Abstract

Constant-potential electrochemical synthesis of ZnO on metal substrates enables selective formation of either Ohmic or Schottky-barrier contacts. Using a mildly acidic nitrate-based aqueous electrolyte, there is a substrate-dependent deposition potential below which electrodeposited ZnO heterojunctions display Schottky response with high contact resistances (∼105Ω) and above which Ohmic behavior and low contact resistances (∼1Ω) occur. Voltammetric evidence for Zn metal deposition, in conjunction with Schottky-barrier heights that are consistent with values expected for a ZnO–Zn junction, suggests that more negative deposition potentials create a Zn-based interface between the substrate and ZnO that leads to rectifying behavior.

The Effect of Synthesis Conditions and Humidity on Current−Voltage Relations in Electrodeposited ZnO-Based Schottky Junctions

“…(This hydrophobicity, consistent with other reports, 35 is due in part to the surface roughness of the electrodeposits. 19,24 ) Assessments of coating continuity and thickness using AFM showed that the hydrophobic layers appear continuous on length scales greater than ∼ 100 nm and typically vary in thickness from 10-60 nm. Pooling of the coating mixture does occur in deep features of the deposit, leading to substantially thicker coatings in some places.…”

Focused-Ion-Beam-Assisted Magnet Fabrication and Manipulation for Magnetic Field Detection Applications

“…Figure 4 shows that ohmic ZnO/substrate contacts form at more positive deposition potentials (with resistances of 1-10 Ω), while rectification occurs in samples prepared at more negative deposition potentials (with resistances of 10 5 -10 6 Ω), consistent with earlier findings. 24 There is also an intermediate range of deposition potentials for which either ohmic response or poor rectification (with pronounced soft breakdown) can result; in other words, there is poor selectivity between linear and rectifying behaviors for these deposition potentials. Nevertheless, the current-voltage response of any single sample is repeatable and does not .…”

“…This pH increase allows the formation of Zn(OH) 2 on the surface of the working electrode, which spontaneously decomposes to ZnO at temperatures above 50 • C. 16,18 Previous work from our group addressed the synthesis conditions required for ZnO electrodeposits displaying either ohmic or rectifying contacts with the underlying conducting metal substrates. 24 In the present work, we identify an expanded range of deposition conditions that can be used to synthesize rectifying ZnO contacts -with dramatically improved performance -by adjusting electrolyte pH. Samples were deposited at potentials ranging from -2.0 V to -0.…”

“…Electrodeposition is a technique that has been used to make ZnO thin films, [15][16][17][18][19] but reports of its electrical resistivity have more often been associated with its function in multilayer systems [20][21][22][23] rather than ZnO alone. 24 Furthermore, none have investigated the impact of humidity changes on electrical responses in electrodeposited ZnO, despite the fact that this synthe-Shawn Chatman and Kristin M. Poduska…”

Lateral Heterogeneities in ZnO Electrodeposits and Their Impact on Electrical and Optical Properties

“…3,4 Control over ZnO electrodeposit epitaxy, texture, morphology, carrier concentration, and orientation has been demonstrated, 2,4 as has selectivity between purely resistive (Ohmic) or rectifying (Schottky) electrical responses. 5,6 Here, we show that electrodeposited rectifying ZnO junctions, fabricated using a well-characterized nitrate reduction route, 3 have spatial (lateral) inhomogeneities that are not apparent using common characterization techniques such as X-ray diffraction or scanning electron microscopy. The origin of this effect is related to incomplete conversion of Zn 2+ to ZnO on some parts of the working electrode during the multi-step electrochemical synthesis process.…”