Effect of Bath pH on Interfacial Properties of Electrodeposited n‐Cu₂O Films

Abstract

For developing semiconductor junction devices with low cost electrodeposited cuprous oxide (Cu 2 O), it will be very useful to investigate possibilities to improve the interface properties of Cu 2 O with suitable junction materials. We have investigated the effect of electrodeposition bath pH on the interfacial properties of n-Cu 2 O/electrolyte, n-Cu 2 O/Au, and n-Cu 2 O/p-Cu 2 O junctions by exploiting capacitance-voltage and photoresponse measurements. In addition, XRD and SEM measurements were also employed for thin film characterization. We have observed that for an increase in bath pH from 5.7 to 6.5 the resulted n-Cu 2 O films produced a shift in the extrapolated flat band potential at the aqueous electrolyte interface by 300 mV. In addition, we have observed that extrapolated built-in potentials at n-Cu 2 O/Au and n-Cu 2 O/p-Cu 2 O interfaces are also affected by the bath pH. With the change in bath pH, the shift in the flat band potential at n-Cu 2 O/electrolyte interface is completely opposite to the builtin potential shift at n-Cu 2 O/Au interface. We explained the observation as a result of the change in net charge at the interfacial surface layers of the interfaces, due to the change in bath pH of the films. Evidence in support of the explanation was further established by the observation that the builtin potential at n-Cu 2 O/Au interface is increased due to the surface modification of n-Cu 2 O films with S 2À ions. In addition, bath pH could be optimized in the fabrication process of Cu 2 O homojunctions to yield high photoactivity. In comparison with the best n-Cu 2 O/Au Schottky junction, we could fabricate a Cu 2 O homojunction with a 590% increase in V oc and an 800% increase in I sc . All the experimental evidences directed toward the idea that the relative band edge position of n-Cu 2 O at the interfaces is affected by the bath pH. The results reported in this investigation will be very useful in the applications of electrodeposited Cu 2 O films in photocataytic, solar cell, and other electronic devices.

Electroplating of Semiconductor Materials for Applications in Large Area Electronics: A Review

“…It is well documented that elemental and compound deposition responds to this chemical dynamic mainly in wet deposition techniques such as chemical bath deposition (CBD) [48] and electrodeposition techniques [49]. With emphasis on electrodeposition, the effect of pH on the bath and the deposited layers vary from selective deposition/etching of element [50], alteration of the characteristic properties of the deposited layers [51,52], elemental/compound precipitation [53], and increase in the deposition current density [54]. Furthermore, the effect of pH on the dissociation of common solvent such as water is also well documented in the literature [55], with the notion that an increase in the acidity of an electroplating bath results in the increase in the concentration of dissociated ions in the aqueous solution [55].…”

Enhanced Photoelectrochemical Water Splitting by Surface Modified Electrodeposited n‐Cu2O Thin Films

“…Therefore, the Fermi level pinning is removed by the surface modification. [ 17,29 ] Thus, the surface modification is able to remove the high density of energetically localized surface states present at the Cu 2 O/electrolyte interface. Still a significant surface recombination of photocarriers exists because, as shown in Figure 2b, the photocurrent onset potential is not equal to but more positive than the flat band potential.…”

P-Type Metal Oxide Semiconductor Thin Films: Synthesis and Chemical Sensor Applications

“…Generally, the annealing temperature controls the structural properties, including phase transition, and hence the optical and electrical properties. For instance, annealing n-Cu 2 O at 500 °C for 30 min in air has been used to transfer n-Cu 2 O into single-phase p-CuO [ 100 , 101 ]. After annealing at 500 °C, a highly porous Co 3 O 4 thin film was grown for integration into supercapacitors [ 102 ].…”