A combination of micro-Raman spectroscopy and micro-XPS (X-ray photo-electron spectroscopy) mapping on statically deflected p-type silicon cantilevers is used to study the mechanical stress dependence of the Fermi level pinning at an oxidized silicon (001) surface. With uniaxial compressive and tensile stress applied parallel to the 110 crystal direction, the observations are relevant to the electronic properties of strain-silicon nano-devices with large surface-to-volume ratios such as nanowires and nanomembranes. The surface Fermi level pinning is found to be even in applied stress, a fact that may be related to the symmetry of the Pb0 silicon/oxide interface defects. For stresses up to 240 MPa, an increase in the pinning energy of 0.16 meV/MPa is observed for compressive stress, while for tensile stress it increases by 0.11 meV/MPa. Using the bulk, valence band deformation potentials the reduction in surface band bending in compression (0.09 meV/MPa) and in tension (0.13 meV/MPa) can be estimated.As silicon devices continue to shrink towards the nanoscale the electronic properties of the silicon/oxide interface, in particular the energy at which the surface Fermi level is pinned, becomes a key factor in the determination of the overall optical and electronic device characteristics [1][2][3][4][5][6]. In parallel with reductions in device size, in-built mechanical stress is widely used to improve the bulk electronic properties of CMOS devices [7], so the question of its effect on surface Fermi level pinning becomes an important one. While there is some evidence from electrical measurements in flash memories [8], MOS capacitors [9, 10] and silicon nano-objects [11][12][13][14], of the way in which stress modifies the surface Fermi level pinning by deep silicon/oxide interface defects, such measurements do not provide direct spectroscopic access to the stress dependence of the pinned Fermi level.The vast literature on electronic spectroscopy of silicon/oxide interface states using surface sensitive techniques [15][16][17][18][19] only includes a small fraction of works which deal with mechanical-stress related effects. Amongst these, experimental studies tend to deal with the consequences of local, bond length strains on the properties of clean, reconstructed surfaces [20,21], while the effect of local strains at the silicon/oxide interface have been studied from a more theoretical perspective [22,23]. In parallel with these photo-emission studies, photo-reflectance has also been used to study strain induced shifts in near-surface electronic energy levels [24][25][26], including a work in which a macroscopic, externally applied stress is used to modify the electronic structure [27]. Although photo-reflectance can be used to estimate surface potential, being an optical technique it is sensitive principally to the mechanical stress dependence of the near-surface, bulk electronic structure.
The steady-state, space-charge-limited piezoresistance (PZR) of defect-engineered, silicon-on-insulator device layers containing silicon divacancy defects changes sign as a function of applied bias. Above a punch-through voltage (V t ) corresponding to the onset of a space-charge-limited hole current, the longitudinal 110 PZR π coefficient is π ≈ 65 × 10 −11 Pa −1 , similar to the value obtained in chargeneutral, p-type silicon. Below V t , the mechanical stress dependence of the Shockley-Read-Hall (SRH) recombination parameters, specifically the divacancy trap energy E T that is estimated to vary by approximately 30 μV/MPa, yields π ≈ −25 × 10 −11 Pa −1 . The combination of space-charge-limited transport and defect engineering that significantly reduces SRH recombination lifetimes makes this work directly relevant to discussions of giant or anomalous PZR at small strains in nanosilicon whose characteristic dimension is larger than a few nanometers. In this limit the reduced electrostatic dimensionality lowers V t and amplifies space-charge-limited currents and efficient SRH recombination occurs via surface defects. The results reinforce the growing evidence that in steady state, electromechanically active defects can result in anomalous, but not giant, PZR.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.