Current Rectification and Photo-Responsive Current Achieved through Interfacial Facet Control of Cu₂O–Si Wafer Heterojunctions

Abstract

Conductive atomic force microscopy (C-AFM) was employed to perform conductivity measurements on a facet-specific Cu2O cube, octahedron, and rhombic dodecahedron and intrinsic Si {100}, {111}, and {110} wafers. Similar I–V curves to those recorded previously using a nanomanipulator were obtained with the exception of high conductivity for the Si {110} wafer. Next, I–V curves of different Cu2O–Si heterostructures were evaluated. Among the nine possible arrangements, Cu2O octahedron/Si {100} wafer and Cu2O octahedron/Si {110} wafer combinations show good current rectification behaviors. Under white light illumination, Cu2O cube/Si {110} wafer and Cu2O rhombic dodecahedron/Si {111} wafer combinations exhibit the largest degrees of photocurrent, so such interfacial plane-controlled semiconductor heterojunctions with light sensitivity can be applied to make photodetectors. Adjusted band diagrams are presented highlighting different interfacial band bending situations to facilitate or inhibit current flow for different Cu2O–Si junctions. More importantly, the observation of clear current-rectifying effects produced at the semiconductor heterojunctions with properly selected contacting faces or planes implies that novel field-effect transistors (FETs) can be fabricated using this design strategy, which should integrate well with current chip manufacturing processes.

Origin and manifestation of semiconductor facet effects

“…Figure 4 shows that electrical connection through a {111}‐bound Cu 2 O octahedron placed on a Si {100} wafer gives perfect current‐rectifying I–V curves, and white light illumination generates photocurrent. [ 45 ] Thus, the fabrication of semiconductor heterojunctions is a plausible design for field‐effect transistors. For the Cu 2 O {110}/Si{111} combination, there is a large photocurrent response, so such structure may have photodetector application.…”

“…(left) Measured I–V curves for a Cu 2 O octahedron on a Si {100} wafer with and without light illumination. (right) Measured I–V curves for a Cu 2 O rhombic dodecahedron on a Si {111} wafer with and without light illumination [ 45 ] …”

“…However, there is no [53] guarantee when two semiconductors are joined together, their photoconductivity should always increase, as the combination of a somewhat conductive Cu 2 O cube and a highly conductive Si {111} wafer is barely conductive even under light illumination. [45] In reality, when Cu 2 O cubes are decorated with ZnO, CdS, ZnS, and Ag 3 PO 4 nanoparticles, the composites remain photocatalytically inactive, attributed to the large band bending of the Cu 2 O {100} faces. [51][52][53][54] The interfacial band bending can be considered to be unmatched to prevent charges from crossing the interface (see Figure 5b,c).…”

Morphological evolution of cadmium oxide crystals showing color changes and facet-dependent conductivity behavior

“…2,19,[26][27][28][29] In addition to the optical facet effect, the absorption band, and hence band gap, can shift continuously from quantum nanostructures to very large particles. [30][31][32] Because these semiconductor facet-dependent properties are interesting and potentially useful, as demonstrated in Cu 2 O-Si wafer heterostructures for current rectification, 33 it is desirable to explore the growth of other polyhedral inorganic crystals such as cadmium oxide to broaden the scope of investigation. CdO is an attractive candidate for shape-controlled particle synthesis with its rocksalt crystal structure and a known band gap of 2.18 eV giving a redbrown appearance.…”

Facet-dependent electrical conductivity properties of a 4H-SiC wafer

“…5 Utilizing the electrical facet effects, current rectification can be achieved through different surface plane or heterojunction combinations of Cu 2 O crystal-Si wafer. 27 This represents a novel design of field-effect transistors. With this potential, it is therefore interesting to extend conductivity measurements to silicon carbide (SiC) wafers for possible facet effects, as it is another third generation semiconductor with a wide band gap, high breakdown electric field and high thermal conductivity characteristics.…”