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

Abstract

Density functional theory (DFT) calculations have been performed on tunable numbers of gallium arsenide (100), (110), and (111) planes for their electron density of states (DOS) plots and the corresponding band diagrams. The GaAs (100) and (110) planes show the same semiconducting band structure with tunable plane layers and a band gap of 1.35 eV around the Fermi level. In contrast, metal‐like band structures are obtained with a continuous band structure around the Fermi level for 1, 2, 4, 5, 7, and 8 layers of GaAs (111) planes. For 3, 6, and 9 GaAs (111) planes, the same semiconducting band structure as seen in the (100) and (110) planes returns. The results suggest the GaAs {111} face should be more electrically conductive than its {100} and {110} faces, due to the merged conduction band and valence band. GaAs (100) and (110) planes give a fixed work function, but the (111) planes have variable work function values that are smaller than that obtained for the (100) and (110) planes. Furthermore, bond length, bond geometry, and frontier orbital electron number and energy distribution show notable differences between the metal‐like and semiconducting plane cases, so the emergence of plane‐dependent electronic properties have quantum mechanical origin at the orbital level. GaAs should possess similar facet‐dependent electronic properties to those of Si and Ge.

Facet-Specific Photocatalytic Activity Enhancement of Cu2O Polyhedra Functionalized with 4-Ethynylanaline Resulting from Band Structure Tuning

“…Thus, one can rationalize the observed photocatalytic facet effects by presenting different degrees of band bending within this surface layer to indicate facet-specific barriers to charge transport across a particular crystal face. The fact that Cu 2 O and Ag 2 O polyhedra possess the same crystal structure but exhibit an opposite facet-dependent photocatalytic activity trend also supports the use of surface layer-induced band structure tuning, rather than surface free energy (γ {110} > γ {111} > γ {100} for Cu 2 O; γ {100} > γ {110} > γ {111} for Ag 2 O) or surface atomic arrangement, as a more general approach to understand the photocatalytic facet behaviors. − Furthermore, DFT calculations on tunable numbers of different Si, Ge, and GaAs lattice planes have revealed that their metal-like and semiconducting faces are related to subtle variations in bond length, bond geometry, and frontier orbital electron distribution within the thin surface layer, which may give rise to differences in the band structure. − …”

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

“…This field-effect transistor (FET) design can be considered as a first-generation approach. To explain the emergence of the observed electrical facet effects, density functional theory (DFT) calculations have revealed the presence of an ultrathin surface layer (∼1 nm or less in thickness) with dissimilar band structures for various surface planes, which should lead to different degrees of surface band bending and facilitate or prevent charge transport across a particular crystal face. ,,,− Furthermore, bond length and bond directions, as well as frontier orbital electron energy distribution, within the thin surface layer can show deviations or variations for the highly conductive crystal faces such as the Si (111) and Cu 2 O (111) planes, which should yield changes in the surface band structure. , These DFT results provide a more physical picture of the thin surface layer. Interestingly, the predicted structural deviations in the surface lattice planes may be observable, as seen in the high-resolution transmission electron microscopy (HR-TEM) images of SrTiO 3 crystals with slight atomic position deviations and noticeable peak shifts in the X-ray diffraction (XRD) patterns of polyhedral Cu 2 O crystals. , To gain further insights, the most conductive Si and Ge {111} wafers were found to have the lowest surface trap state population and the shortest carrier lifetime, matching with their best electrical conductivity behavior. , GaAs wafers, however, do not show such surface trap state and carrier lifetime correlation to their conductivity properties …”

Semiconductor nanocrystals possessing broadly size‐ and facet‐dependent optical properties

“…[5,6] Density functional theory (DFT) calculations on tunable numbers of different lattice planes of Cu 2 O, Ag 2 O, PbS, Si, Ge, and GaAs have suggested that there is a thin surface of generally below 2 nm with surface-specific band structures. [7][8][9][10][11][12] DFT calculations on Si, Ge, and GaAs further reveal that there are subtle variations in the bond length, bond geometry, and frontier orbital electron number and energy distribution within the thin layer for surfaces giving semiconducting and metal-like band structures. Thus, one can envision that there is a facespecific thin layer for semiconductor materials with different band structures resulting from subtle variations at the bond and orbital levels.…”