Boron in amorphous silicon: an ab initio study
نویسندگان
چکیده
We have performed an ab initio study of B in amorphous Si by analyzing different substitutional(a Si atom in the amorphous cell is replaced by a B atom, Bs) and interstitial-like (a B atom is added into an interstitial space, Bi) configurations. We find substitutional-like B (Bs and Bi that relaxes to four-fold coordination) with negative charge to have the lowest chemical potential at mid-gap, with a linear scaling of the Bs chemical potential with the average nearest-neighbor distance. The negative charge-state confirms the unexpected (but experimentally observed) capability of doping amorphous Si. Non-fourfold Bi atoms have an averaged formation energy of 1.5 eV at mid-gap. A molecular dynamics study with subsequent nudged-elastic band optimization results in a migration barrier of ∼ 0.6 eV and an activation energy of 2.1 eV which is in the experimental range. PACS numbers: 31.15.A-, 81.05.Gc, 85.40.Ry
منابع مشابه
Energetics of Hydrogen in Amorphous Silicon: an ab initio study
Using ab initio density functional calculations, we investigate the energetics of hydrogen in amorphous silicon. We compare a hydrogen at a silicon bond center site in a-Si to one in c-Si. In addition, we identify the energetics of the dominant traps for H in a-Si. The present calculations are used to elucidate many experiments and concepts regarding hydrogen in amorphous silicon.
متن کاملAb initio simulation of first-order amorphous-to-amorphous phase transition of silicon
The pressure-induced phase transition in amorphous silicon ~a-Si! is studied using ab initio constantpressure molecular-dynamic simulations. Crystalline silicon ~c-Si! shows a phase transformation from diamond-to-simple hexagonal at 29.5 GPa, whereas a-Si presents an irreversible sharp transition to an amorphous metallic phase at 16.25 GPa. The transition pressure of a-Si is also calculated fro...
متن کاملThermally driven hopping and electron transport in amorphous materials from density functional calculations
In this paper we study electron dynamics and transport in models of amorphous silicon and amorphous silicon hydride. By integrating the time-dependent Kohn–Sham equation, we compute the time evolution of electron states near the gap, and study the spatial and spectral diffusion of these states due to lattice motion. We perform these calculations with a view to developing ab initio hopping trans...
متن کاملApproximate ab initio calculation of vibrational properties of hydrogenated amorphous silicon with inner voids
We have performed an approximate ab initio calculation of vibrational properties of hydrogenated amorphous silicon (a-Si:H) using a molecular dynamics method. A 216-atom model for pure amorphous silicon (a-Si) has been employed as a starting point for our a-Si:H models with voids that were made by removing a cluster of silicon atoms out of the bulk and terminating the resulting dangling bonds w...
متن کاملFirst-Principles Study of Boron Diffusion in Silicon
In this Letter we investigate boron diffusion as a function of the Fermi-level position in crystalline silicon using ab initio calculations. Based on our results, a new mechanism for B diffusion mediated by Si self-interstitials is proposed. Rather than kick out of B into a mobile channel, we find a direct diffusion mechanism for the boron-interstitial pair for all Fermi-level positions. Our ac...
متن کامل