Silicon Wafers with Facet‐Dependent Electrical Conductivity Properties

Abstract

By breaking intrinsic Si (100) and (111) wafers to expose sharp {111} and {112} facets, electrical conductivity measurements on single and different silicon crystal faces were performed through contacts with two tungsten probes. While Si {100} and {110} faces are barely conductive at low applied voltages, as expected, the Si {112} surface is highly conductive and Si {111} surface also shows good conductivity. Asymmetrical I-V curves have been recorded for the {111}/{112}, {111}/{110}, and {112}/{110} facet combinations because of different degrees of conduction band bending at these crystal surfaces presenting different barrier heights to current flow. In particular, the {111}/{110} and {112}/{110} facet combinations give I-V curves resembling those of p-n junctions, suggesting a novel field effect transistor design is possible capitalizing on the pronounced facet-dependent electrical conductivity properties of silicon.

Density Functional Theory Calculations Revealing Metal‐like Band Structures for Ultrathin Germanium (111) and (211) Surface Layers

“…[7,11,[16][17][18] To verify that the facet-dependent electrical-conductivity phenomenon is broadly observable in semiconductors, electrical-conductivity measurementsh ave been made on four different faces of Si wafers, which revealed that the (111)a nd (112) surfaces are highly conductive. [19] The results are consistent with previous DFT calculations showing metal-like band structuresf or these two Si surfaces. [20] Because germanium is also an important wafer material, knowing the presence of facet-dependent electrical properties of germanium should be quite useful for novel integrated circuit fabrication.…”

“…Figure offers band structures of one to three layers of Ge(211) planes, the corresponding DOS plots, and side‐ and top‐view models of the Ge(211) planes. Since germanium and silicon have the same crystal structure, the previous assignment of the Si(112) plane could have been changed to Si(211) planes according to the presence of the (422) peak in the X‐ray diffraction pattern of silicon . The Supporting Information provides band structures of four to six layers of Ge(211) planes, the corresponding DOS plots, and models of the Ge(211) planes.…”

“…Since germanium and silicon have the same crystal structure, the previous assignment of the Si(112) plane could have been changed to Si(211) planes according to the presence of the (422) peak in the X-ray diffraction pattern of silicon. [19,20] The Supporting Information provides band structures of four to six layers of Ge(211) planes, the corresponding DOS plots, and modelso ft he Ge(211) planes. Again, valence-band and conduction-band energies cross each other for one and two layers of Ge(211) planes, thereby yieldingm etal-like band structures.…”

“…As the ultrathin layer has dissimilar band structures for different crystal faces it means that light of somewhat different wavelengths is absorbed by particles of various shapes, accounting for the observed facet‐dependent optical properties of Cu 2 O and other semiconductor crystals . To verify that the facet‐dependent electrical‐conductivity phenomenon is broadly observable in semiconductors, electrical‐conductivity measurements have been made on four different faces of Si wafers, which revealed that the (111) and (112) surfaces are highly conductive . The results are consistent with previous DFT calculations showing metal‐like band structures for these two Si surfaces .…”

Density Functional Theory Calculations Revealing Metal‐like Band Structures and Work Function Variation for Ultrathin Gallium Arsenide (111) Surface Layers

“…For example, a Cu 2 O octahedron is highly conductive, but a single Cu 2 O rhombic dodecahedron is insulating. More recently, intrinsic Si and Ge wafers have also revealed facet‐dependent electronic properties . All these semiconductors, including Ag 3 PO 4 crystals, display current‐rectifying effects when electrical contacts are made on two different crystal faces .…”