Electro-optical properties of APS and APhS linkers on silicon thin film: A DFT study

[Display omitted] •APS linker shifts the band edges less than APhS.•〈111〉 silicon as a substrate is less affected by linker molecules than 〈100〉 silicon.•OH molecules causes surface orbitals to sink deep into the substrate.•Added surface states can enhance carrier transport on the silicon surface. APS (3-Aminopropyl) trimethoxysilane) and APhS (p-Aminophenyl) trimethoxysilane) are the most commonly used linkers on a silicon surface. We investigate the surface properties of the structures, including APS or APhS on a silicon substrate. The studied structures consist of APS or APhS linkers with one, two, or three bonds with a substrate, which is a thin layer of Si with crystal orientation 〈100〉 or 〈111〉. Using a first-principles study based on density functional theory (DFT), we investigated the electronic and optical properties of the silicon-linker interface, such as interface states, orbital location, dielectric function, and photon absorption. The effects of linker type, number of linker-substrate bonds, and crystal orientation on density of states are investigated as a most important electrical property. In addition, we calculated the orbital location and dielectric function in the structures consisting of the substrate with the linker molecules. In this study, we propose techniques to reduce band edge shifts due to surface states and enhance the current mobility in structures with APS or APhS on a silicon substrate. The obtained results show that the use of APS linker molecules instead of APhS can reduce the conduction band shift by up to 50% and the density of interface states are sharply reduced at a depth of approximately 5 Å from the silicon surface. Also, simulation results show that the effect of linkers on the dielectric function can be negligible in the case of using linkers with one or two bonds with the substrate at low energies (lower than 5 eV).