Ab Initio Investigation of Charge Trapping Across the Crystalline- Si –Amorphous- SiO2 Interface

Abstract

Accurate microscopic description of the charge trapping process from semiconductor to defects in dielectric oxide layer is of paramount importance to understanding many microelectronic devices like the complementary metal-oxide-semiconductor (CMOS) transistors, as well as electrochemical reactions. Unfortunately, most current microscopic descriptions of such processes are based on empirical models with parameters fitted to experimental device performance results or simplified approximations like the Wentzel-Kramers-Brillouin (WKB) method. Some critical questions are still unanswered, including: What controls the charge hopping rate, the coupling strength between the defect level to semiconductor level, or the energy difference? How does the hopping rate decay with defect-semiconductor distance? What is the fluctuation of the defect level, especially in amorphous dielectrics? Many of these questions can be answered by ab initio calculations. However, till date, there are scarce ab initio studies for this problem mainly due to technical challenges from atomic structure construction to large system calculations. Here, using the latest advance in calculation methods and codes, we have studied the carrier trapping problem using density functional theory (DFT) based on the Heyd-Scuseria-Ernzerhof (HSE) exchange correlation functional. The valence bond random switching method is used to construct the crystalline-Si/amorphous-SiO 2 (c-Si/a-SiO 2) interfacial atomic structure, the HSE yields band offset agrees well with experiments. The hopping rate is calculated with the Marcus theory, and the hopping rate dependences on the gate potential and defect distances are revealed, as well as the range of fluctuation results from amorphous structural variation. We have also analyzed the result with the simple WKB model and found major difference in the description of the coupling constant decay with the defect-semiconductor distance. Our results provide the ab initio simulation insights for this important carrier trapping process for device operation.

First principles study of Schottky barriers at Ga2O3(100)/metal interfaces

“…All calculations, including geometry optimization and electronic structure calculation, were performed with the Norm-Conserving Pseudopotential (NCPP) implemented in the plane-wave package PWmat code 27,28 which has been proven to be an accurate and efficient package to calculate large semiconducting systems. 29 The Perdew-Berk-Ernzerhof (PBE) exchange-correlation functional was used 30,31 to optimize the structure with a plane wave energy cutoff of 60 Ryd. The Monkhorst-Pack k-point mesh was set to 3 Â 2 Â 1 for the model of 98 atoms, and the force threshold was set to 0.02 eVÅ À1 .…”

Characterizing the Charge Trapping across Crystalline and Amorphous Si/SiO 2 /HfO 2 Stacks from First-Principle Calculations

“…Moreover, the WKB approximation has only been used in single-interface systems such as Si/SiO2, and its validity in multiple-interface systems is quite questionable (as the wave function can be bounced by at the interface). Even in single-interface Si/SiO2 system, our previous work has shown that the WKB approximation can underestimate the coupling strength of two states [18].…”

“…As discussed in one of our previous studies on charge trapping across Si/SiO2 interfaces [18], the accurate atomistic simulation of the charge trapping process is possible only after a few technical challenges have been overcome. These include realistic interface structures, correct theoretical band alignment, and the application of adequate charge transfer theories.…”

“…The coupling strength between the two states also plays an important role [17,25]. It has been proved that the coupling strength is especially important when the initial state and final state are close in energy [18]. Third, the energy level of charge trapping defect in the dielectric layer depends greatly on the applied gate voltage, and so does the energy difference between these defect levels and the Si band edge.…”

Some recent advances in ab initio calculations of nonradiative decay rates of point defects in semiconductors

“…Marcus theory is also often used to describe electron transitions from one state to another, especially for electronic states located at different positions 17 . While the energy barrier of the Marcus theory also comes from atomic displacements (hence the diagonal elements of electron-phonon coupling), the electronic coupling can come from different sources, e.g., an applied electric field, or more intrinsic coupling.…”