To read the full-text of this research, you can request a copy directly from the authors.
... This is the reason why signals of strongly coupled spin pairs in principle should not be detectable with EDMR. Only if intersystem crossing (ISC)  from the triplet to the singlet manifold is made possible by, e.g., spin-orbit coupling (SOC) [32,33] or if a third spin is involved in the spin-dependent process , singlet pair population is generated and the induced current change can be observed as an EDMR signal. ...
... Here, SOC can play an important role. Alternatively, coupling to an additional spin which goes along with coupled spin states could promote triplet-to-singlet conversion, as already suggested for other systems [10,34]. The additional spin needs to be spatially close to the TE spin to achieve a sufficiently strong interaction. ...
Electrically detected magnetic resonance (EDMR) spectroscopy is employed to study the influence of triplet excitons on the photocurrent in state-of-the-art microcrystalline silicon thin-film solar cells. These triplet excitons are used as sensitive spin probes for the investigation of their electronic and nuclear environment in this mixed-phase material. According to low-temperature EDMR results obtained from solar cells with different Si29 isotope concentrations between 0.01% and 50%, the triplet excitons reside at extended defects in the crystallites of microcrystalline silicon that give rise to shallow states in the silicon band gap. The excitons possess a rather delocalized wave function, couple to electron spins in conduction band tail states nearby, and take part in a spin-dependent recombination process. Our study shows that extended defects such as grain boundaries or stacking faults in the crystalline part of the material act as charge carrier traps that can influence the material conductivity.
The interfaces between high-κ dielectrics, grown by atomic layer deposition, and semiconductors have been characterized using various electrically detected magnetic resonance spectroscopy techniques. The dominant center at the interface was found to be Pb0-like. Microwave contactless photoconductive resonance and defect-assisted spin dependent tunneling spectroscopies, performed at low temperatures, reveal also a signal which could be related to E’-like near interfacial oxide traps.
The effects of external magnetic-field modulation as well as microwave-power modulation on the signal intensity and line-shape are considered for an electrically detected magnetic resonance signal. It is shown that the signal increases in amplitude and then splits into two lines with increasing magnetic-field-modulation amplitude. A theory is developed which fits the experimental results extremely well and it is concluded that the double modulation can be used to obtain information about component lines as well as to enhance signal-to-noise.
The microstructural features of the Si-SiO2 system and the chemical physics of its defects are reviewed and examined. Topics are grouped by scientific commonality, rather than by the usual technological manifestations. The role of atomic and molecular sized entities is emphasized, and the latter are limited to those containing only Si, O, H, or combinations thereof. Most of the reported researches involve x-ray or electron diffraction, Auger or photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, or capacitance-voltage or deep-level transient spectroscopy. Several forms of crystalline and amorphous vitreous silica are considered as a basis for discussion of thin film thermal silica on silicon wafers. Local lattice symmetry, stoichiometry, bond lengths and angles, vacancies and voids, dangling orbital centres, and fixed and migratory hydrogen species are treated extensively. Elements of relevant theory are summarized. Overall, it is hoped to provide a solid data base for future development of general models for essential electronic phenomena in the Si-SiO2 system.
This paper discusses the defect structure of MOS device materials, in particular the evidence relating to dangling bond defects at the Si/SiO2 interface. Over two decades and more, the characterisation of such defect states has given information on paramagnetic (S=1/2) centres at the interface. The most remarkable feature of the thermally oxidised Si surface is the very small density of interface defects ( approximately 1015 m-2) compared to the bare semiconductor surface. These states have energies throughout the Si band gap, and their charge may be changed by changing the Fermi level in the band gap. Ionic contamination of the thermal oxide may affect the electrostatics of the MOS material. Some ionic defects (such as Na+) move under the influence of an applied field and cause device characteristics to drift with time, in addition there is a positive 'fixed oxide charge' located within about 3 nm of the Si/SiO2 interface. Other centres exist throughout the bulk of the oxide, which can trap both positive and negative charge. The control of interface state density and oxide charge density is extremely important for the production of reliable devices. Given the very small defect levels, rather sensitive techniques have to be used to measure the concentration and characterise the structure of defects in Si/SiO2 materials. Here the authors discuss the use of spin-dependent spectroscopies such as electron spin resonance, optical detection of magnetic resonance and spin-dependent recombination as aids to elucidating defect structure. They also discuss some experiments on p-channel MOSFETS in which an inversion layer of holes is created at the interface when turned on by a sufficiently negative gate voltage. Inversion layers in MOSFETS at low temperatures are used for the investigation of conduction in two dimensions. Such experiments at low temperatures on the localisation of carriers are shown here to give information on both positive and negative charge trapped near the interface.
High mobility substrates and silicon nanowires are important key elements in the development of advanced devices targeting a vast range of functionalities. In almost all applications the interface between the semiconductor and the oxide layer placed on top or all around plays a crucial role in determining the device performance. The investigation of defects at these interfaces is therefore mandatory to fully exploit the advantages of these systems. We report on the application of electrically detected magnetic resonance (EDMR) techniques in the investigation of defects at the interface between Ge and GeO2 (or GeOx) and at the interface between silicon nanowires (SiNWs) and SiO2.Graphical abstractHighlights► Defects at the GeOx/Ge interface. ► Defects at the Si nanowire/SiO2 interface. ► Electrically detected magnetic resonance.
Previous theories to explain the variation of photoconductivity upon saturation of electron spin resonance, as observed by Lépine in silicon, predict an effect 10 to 100 times smaller than experiment. In the present model we show that, due to the shorter lifetime of electron-hole pairs in singlet configuration, the steady state spin distribution shows a surplus of triplet pairs. Saturation of resonance restores the random distribution, resulting in a shortening of the recombination time. The relative variation can be as large as 10 %, and is field independent as confirmed by experiment. Les théories précédentes concernant la variation de photoconductivité à la résonance de spin (expériences de Lépine dans le silicium) prédisent un effet de 10 à 100 fois trop faible. Nous proposons un modèle où, par suite du temps de vie plus court d'une paire électron-trou en configuration singulet, la distribution des spins des paires contient un surplus d'états triplets. Ce surplus est supprimé par saturation de la résonance, ce qui raccourcit ainsi le temps de recombinaison. La variation peut atteindre 10 % et l'effet ne dépend pas du champ appliqué, en accord avec l'expérience.
Energy distribution of P b centers (∙Si≡Si 3 ) and electronic traps (D it ) at the Si/SiO 2 interface in metal‐oxide‐silicon (MOS) structures was examined by electric‐field‐controlled electron paramagnetic resonance (EPR) and capacitance‐voltage (C‐V) analysis on the same samples. Chips of (111)‐oriented silicon were dry‐oxidized for maximum P b and trap density, and metallized with a large MOS capacitor for EPR and adjacent small dots for C‐V measurements. Analysis of C‐V data shows two D it peaks of amplitude 2×10<sup>1</sup><sup>3</sup> eV<sup>-</sup><sup>1</sup> cm<sup>-</sup><sup>2</sup> at E v +0.26 eV and E v +0.84 eV. The EPR spin density reflects addition or subtraction of an electron from the singly occupied paramagnetic state and shows transitions of amplitude 1.5×10<sup>1</sup><sup>3</sup> eV<sup>-</sup><sup>1</sup> cm<sup>-</sup><sup>2</sup> at E v +0.31 eV and E v +0.80 eV. This correlation of electrical and EPR responses and their identical chemical and physical behavior are strong evidence that ∙Si≡Si 3 is a major source of interface electronic traps in the 0.15–0.95 eV region of the Si band gap in unpassivated material.
The first observation of spin-dependent thermal emission from a deep gap state in a semiconductor is reported. As a result the silicon dangling-bond defects at the Si/SiO2 interface can be directly correlated with a 0.36-eV-deep hole trap.
Like the spin-denendent photoconductivity in pure silicon, the current of a silicon n+-p junction is found to be affected by electron spin resonance. The experiment shows that the same centers are responsible for the recombination in the diode and in pure silicon, that only the recombination in the space-charge region of the junction is spin-dependent and that the effect in this region is very large. A tentative model for the electron-hole recombination in silicon is proposed.
It is shown that, in pure silicon, the recombination time of photocreated excess carriers depends on the relative spin orientation of the carriers and of the recombination centers. This is evidenced by the observed decrease of the photoconductivity when the magnetization of the recombination centers is reduced. Several experiments show independently that the spin-dependent recombination mechanism involves surface states: (i) Reducing the magnetization of the recombination centers through spin resonance leads to a resonant change of the height of the surface potential barrier. (ii) The size of the effect on photoconductivity increases when surface recombination is favored with respect to bulk recombination. The change in photoconductivity when the magnetization of the surface recombination centers is saturated, provides a means to observe the spin resonance of these centers with a good signal-to-noise ratio, whereas the conventional electromagnetic detection does not yield any observable signal. One thus obtains an order of magnitude for the spin-lattice relaxation time of the centers T1≈10-6 sec and an upper limit for their density Nt≲1012/cm2.
We present the results of an investigation of spin dependent recombination in (100) oriented, gate controlled Si diodes irradiated by 30 keV electrons. After irradiation, recombination at the SiSiO2 interface is increased, and saturation of the spin resonance increases the diode forward current by 5 parts in 104. The results cannot be described by a conventional Shockley-Read recombination model. An alternative picture is proposed involving recombination between trapped electrons and trapped holes.
The EPR signal P b from interface Si<sup>III</sup> centers in oxidized (111) and (100) silicon wafers has been observed to be enhanced up to 20 times under illumination with white light at liquid‐nitrogen temperature. The enhanced EPR signal saturates normally with microwave power, much like its unenhanced counterpart, which indicates that it is not a photoconductive pseudo‐EPR signal, as observed for other silicon surface defects. It is suggested that the effective spin polarization of Si<sup>III</sup> centers is changed by the light. The optical effect, however, shows complications which may reflect coupling between the P b center and the semiconductor carriers.
We report studies of spin???dependent recombination at the Si/SiO 2 interface in electron irradiated (100) and (111) p???channel metal???oxide???silicon field???effect transistors and metal???oxide???silicon wafers. Electron spin resonance transitions on the P b center increase the recombination current at the Si/SiO 2 interface by 2???3 parts in 10<sup>4</sup>. The results are interpreted using a model involving the recombination of electrons and holes at P b centers with which they are spatially correlated.
The hyperfine spectrum associated with unpaired electrons at the (111) Si/SiO 2 interface (P b centers) is reported for the first time. Electron paramagnetic resonance measurements indicate that the hyperfine interaction S↘∙Ā∙I↘ arises from the <sup>2</sup><sup>9</sup>Si isotope and is characterized by A ‖ =146.(±5.)×10<sup>-</sup><sup>4</sup> cm<sup>-</sup><sup>1</sup> and A ⊥ =85.(±8.)×10<sup>-</sup><sup>4</sup> cm<sup>-</sup><sup>1</sup>. An analysis of this hyperfine interaction firmly establishes many of the details in the structure of this interface defect.
Electron spin resonance measurements have been made on gamma‐irradiated (111) Si/SiO 2 structures as a function of bias across the oxide. We observe a large change in the density of radiation‐induced paramagnetic P b centers with bais. We conclude that P b defects (trivalent silicons at the Si/SiO 2 interface) account for a very large portion of the radiation‐induced interface states.