G. J. Gerardi

Electronic traps and Pb centers at the Si/SiO2 interface: Band‐gap energy distribution

Energy distribution of Pb centers (⋅Si≡Si3) and electronic traps (Dit) at the Si/SiO2 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 Pb 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 Dit peaks of amplitude 2×1013 eV−1 cm−2 at Ev+0.26 eV and Ev+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 1.5×1013 eV−1 cm−2 at Ev+0.31 eV and Ev+0.80 eV. This correlation of electrical and EPR responses and their identical chemical and physical behavior are strong evidence that ⋅Si≡Si3 is a major source of interface electronic traps in the 0.15–0.95 eV region of the Si band gap in unpassivated material.

Interface traps and Pb centers in oxidized (100) silicon wafers

The band‐gap energy distribution of Pb centers on oxidized (100) Si wafers has been determined and compared with interface electrical trap density Dit. Two different Pb centers are observed on (100) Si: Pb0, which has the structure ⋅Si≡Si3, and is essentially identical to the sole Pb center observed on (111) Si; and Pb1, of presently uncertain identity, but clearly different in nature from Pb0. By electric field‐controlled electron paramagnetic resonance (EPR) and capacitance‐voltage (C‐V) measurements, it is found that Pb0 has its (0↔1) electron transition at Ev+0.3 eV and its (1↔2) transition at Ev+0.85 eV. Similarly, Pb1 has its (0↔1) transition at Ev+0.45 eV and its (1↔2) transition at Ev+0.8 eV. The Pb band‐gap density correlates qualitatively and quantitatively with the electrical trap density Dit from C‐V analysis; nonbonded Pb orbitals are found to be the source of about 50% of the characteristic traps in dry‐oxidized, unannealed (100) Si wafers.

Structural identification of the silicon and nitrogen dangling-bond centers in amorphous silicon nitride

We report the observation of both silicon and nitrogen paramagnetic defect centers using X‐band and Q‐band electron spin resonance microwave excitation frequencies. By using two different microwave frequencies along with a computer analysis of the resonance lineshapes, we have been able to confirm and extend earlier observations regarding the chemical identity of these paramagnetic defects. Specifically, we provide additional evidence that the silicon dangling bond, i.e., K center, is an unpaired electron on a silicon atom bonded to three nitrogen atoms in stoichiometric silicon nitride. We further demonstrate that the g tensor of the K center exhibits very little anisotropy and that the lineshape is broadened primarily by hyperfine interactions of the nitrogens bonded to the silicon atom. We also confirm that the recently observed nitrogen dangling‐bond resonance in silicon nitride is indeed due to a hyperfine interaction with a nitrogen nucleus. This improved understanding of these two important paramagnetic defects may be of importance in eliminating or perhaps exploiting their chemical properties.

An electron paramagnetic resonance study of electron injected oxides in metal‐oxide‐semiconductor capacitors

Electron paramagnetic resonance, in conjuction with electrical measurements, has been used to study Si‐SiO2 interface defects produced as a result of negative bias, high‐field electron injection into the SiO2 layer of metal‐oxide‐semiconductor capacitors. In particular, a search was made for Pb centers, previously identified as a source of interface traps in unannealed SiO2 on Si, and for E’ centers, which have been associated with trapped holes in SiO2. The results of the EPR experiments show no change in the density of Pb centers following injection, despite the presence of interface traps as indicated by the electrical measurements. Further, no E’ centers are detected in samples for which an analysis of the current‐voltage and capacitance‐voltage data suggest the presence of 5×1012 cm−2 positively charged centers. We conclude that interface traps generated in the present samples are not of the same microscopic nature as those found in unannealed SiO2 on Si, and that positive charging under the present ...

Generation of P sub b centers by high electric fields; Thermochemical effects

The generation of P{sub b} centers by negative corona charging has been examined by electron spin resonance (ESR). Formation of P{sub b} centers has been found to saturate in about 25s. The corona-generation effect is maximized for samples oxidized in ambients containing about 0.1% H{sub 2}O, and disappears with dry or steam-growth oxides. Mild postoxidation anneals can also generate P{sub b} in these samples, and the activation energy for this thermal generation is lowest for samples showing the corona effect. Prolonged anneals have been found to passivate existing P{sub b} and, ultimately, to produce an interface that is very resistant to corona depassivation. It is proposed that the P{sub b} generation is due to weakening of the interface Si-H bond by attraction of a hole from the Si bulk in the negative field, followed by prompt abstraction and capture of a proton by a nearby H{sub 2}O molecule to yield H{sub 3}O{sup +} and P{sub b}. Capacitance-voltage curves show flatband shifts and stretchout, which indicate the generation of positive oxide charge and interface states.

Nature of Pb‐like dangling‐orbital centers in luminescent porous silicon

The Pb‐like dangling‐orbit centers in luminescent porous silicon (LPSi) have been enhanced to very high concentration (1015 cm−2) by gentle oxidation. High signal‐to‐noise ratio and very sharp lines enable the g‐value maps, and 29Si hyperfine and superhyperfine structures to be clearly resolved by ordinary EPR. Only one Pb‐like center is observed, and it is proven to be of the Pb0 variety (⋅Si≡Si3). The relative EPR signal strengths from different g limbs indicate that the LPSi crystallite morphology is not dominated by needles or platelets.

Electrically detected magnetic resonance of a transition metal related recombination center in Si p–n diodes

A hyperfine structure has been observed by electrically detected magnetic resonance from a Si p–n diode. From the hyperfine splitting, and the natural abundance of the interacting I=1/2 nuclear species, the recombination center is found to be consistent with a platinum complex.

Electrically detected magnetic resonance in p-n junction diodes

Abstract Electrically-detected magnetic resonance from spin-dependent recombination or generation has been observed in various Si p-n junction diodes. The g-values varied widely among similar diodes of different manufacture; most differed from Si damage at g ≈ 2.0055 reported by other researchers. The lowest g-value (1.965) is out of the range of carrier, band-tail, and dangling Si orbital centers; it may indicate metallic ions.

Electron paramagnetic resonance of porous silicon: Observation and identification of conduction-band electrons

New features in electron paramagnetic resonance (EPR) of porous silicon have been examined here. A new isotropic EPR center was observed at g=1.9995(1) at T=4.2 K, in both p-type and n-type porous silicon. By comparing its g value with those of shallow donors in bulk silicon, the center was identified due to the conduction-band (CB) electrons in silicon microcrystals. The CB signal, present in freshly prepared p-type and n-type samples, can be dramatically and surprisingly enhanced by the presence of a polar solvent on the n-type porous silicon surface. Even though it was shown that most of the donor electrons in an n-type sample can be pulled into the porous layer from the substrate by solvent exposure of the porous layer, the possible electrochemical effects are not yet completely understood; to establish a reasonable model for them would require appropriately controlled experiments.

PARAMAGNETIC CENTERS AND DOPANT EXCITATION IN CRYSTALLINE SILICON CARBIDE

Impurities, point defects, and dopant excitation in SiC have been examined by electron paramagnetic resonance (EPR). The pervasive nitrogen n-type dopant was found to show a substantial photo-enhancement, not due to generation of carrier pairs. Aluminum in Al-doped SiC showed a strong EPR signal below 4 K, which disappeared as the sample was warmed to 10 K, because of the onset of impurity band conduction. The Al EPR signal intensity depends on the degree of compensation. Boron EPR appeared in samples where excess Al counteracts the compensation of B ions by N dopant. Hydrogen plasma anneal at 250 °C partially passivated Al; however, extended heating in vacuum, expected to depassivate, actually further decreased the Al signal. Abrasion damage produced a featureless, isotropic signal suggestive of the bulk damage signal in Si, indicating dangling C or Si orbitals. An oxide interface signal, in analogy to Pb of oxidized Si, was not isolated; the observed signal included a damage-like line.