Neutral Dangling Bond Research Articles

Defects in porous p-type Si: An electron-paramagnetic-resonance study.

The defects in ${\mathit{p}}^{+}$ porous silicon of low and high porosity have been studied by using electron-paramagnetic-resonance (EPR) spectroscopy and compared with an impurity analysis obtained from nuclear reaction analysis (NRA). The EPR measurements show, in both high- and low-porosity samples, the same dominant paramagnetic defect which we have identified from its g tensor and hyperfine tensor as the trigonal (111) ${\mathit{P}}_{\mathit{b}}$ center; the neutral dangling bond at the Si/${\mathrm{SiO}}_{2}$ interface. The symmetry of the central Si hyperfine-interaction tensor has been determined. From the defect concentration it is estimated that about 50% of the surface of p-type porous Si exposed to air is oxidized. The symmetry of the EPR spectrum of the ${\mathit{P}}_{\mathit{b}}$ center relative to the substrate proves the monocrystalline character of the oxidized surface with a preferential (111) orientation. In as-grown and aged samples a high fraction (g0.95) of the ${\mathit{P}}_{\mathit{b}}$ centers are passivated by H. They are depassivated by a thermal anneal at 400 \ifmmode^\circ\else\textdegree\fi{}C under ultrahigh vacuum, revealing total ${\mathit{P}}_{\mathit{b}}$-center concentrations of some ${10}^{11}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. Independent of porosity both types of sample were found, by using NRA, to be heavily contaminated by H, C, and O with impurity-atom to Si-surface-atom ratios of 0.3 to 0.6, 0.1, and 0.01, respectively. The 80%-porosity samples, the only ones showing room-temperature visible photoluminescence, contain, in addition, amorphous Si inclusions; their presence is deduced from the observation of the g=2.0055 dangling-bond centers in thermally annealed samples. As ${\mathit{P}}_{\mathit{b}}$ centers are recombination centers, efficient photoluminescence in 80%-porosity samples, in which surface properties are predominant, requires a minimization and stabilization of these defects.

Energy Differences Between the Si and the Ge Dangling Bond Defects in a-Si1-xGex Alloys

ABSTRACTWe have investigated the difference in the electronic energies of neutral Si and Ge dangling bond states in undoped a-Si1-xGex alloys as a function of the alloy composition, x, and local bond-angle distortions. The local density of states, LDOS, in a-Si1-xGex alloys has been calculated using nearest-neighbor interactions, and employing the Cluster Bethe Lattice method. We conclude that for ideal, tetrahedrally bonded amorphous semiconductors alloys, the Ge dangling bond energy is lower than that of Si dangling bonds by ∼ 0.13 eV, independent of the specific nearest neighbors to the dangling bond (3 Si-atoms, 2 Si-atoms and 1 Ge-atom, etc.), but that the spread in dangling bond energies associated bond-angle variations of the order of 6–8 degrees can be larger than this energy difference (∼0.3 eV or greater). This means that structural disorder, rather than chemical disorder causes Si and Ge-atom dangling bond states to overlap in their energy distributions.

Defect States and Structural Disorder in a-Si.

ABSTRACTWe have examined the distribution of the neutral dangling bond defect states, T30, as a function of the local disorder. T30 defects in a-Si play an important role in many of the current models of the metastable photoconductivity. To understand the relationship between the T30 defect and its bonding environment, the Local Density of States (LDOS) for under-coordinated Si atoms in disordered environments are calculated using the cluster-Bethe lattice method, CBLM. Our Hamiltonian employs the tight-binding parameters of an sp3 orbital basis containing both 1st and 2nd nearest-neighbor interaction terms fit to c-Si band structure. Averaged LDOS of atoms with various bond angle distortions are calculated in order to demonstrate the relationship between the standard deviation in bond angle and the width of the defect states. The CBLM is also used to determine the extent of the valence band tails as a function of the standard deviation in bond angle. In addition, the LDOS of clusters with 2 dangling bonds are examined to determine the degree that their energy levels split due to their interaction with each other.

Experimental studies of the light-induced effects in undoped hydrogenated amorphous silicon as a function of deposition conditions

Experimental studies of the light-induced effects in undoped hydrogenated amorphous silicon as a function of deposition conditions

Thermal Annealing of Light-Induced K Centers in Hydrogenated Amorphous Silicon Nitride

ABSTRACTThe thermally-induced decay of light-induced, paramagnetic neutral silicon dan-gling bonds(K centers ) in hydrogenated amorphous silicon nitride thin films is monitored using electron spin resonance. The nitride films are of gate-quality and nitrogen-rich and are deposited at two different temperatures (250 and 400 °C). The kinetics for isothermal annealing of the light-induced K° states is dependent upon sample deposition temperature and is observed to follow a stretched exponential dependence, exp {— (t/τ)β}, upon annealing time (t). The stretched exponential factor, β, shows a non-linear dependence upon annealing temperature including temperature independent regimes. Thermal annealing is thermally activated with an apparent activation energy of ∼ 0.4 eV and is independent of deposition temperature. These results indicate that annealing is a dispersive process which involves hopping and multiple trapping or trap controlled hopping in the thermal annealing of light induced K centers in amorphous SiN1.6:H.

Evidence for the dominance of charged dangling bond defects in the photodegradation of hydrogenated amorphous silicon

Evidence for the dominance of charged dangling bond defects in the photodegradation of hydrogenated amorphous silicon

Explosive isothermal hydrogen exodiffusion in VHF-GD a-Si:H thick layers

Explosive isothermal hydrogen exodiffusion in VHF-GD a-Si:H thick layers

The optoelectronic properties of a-Si, Ge:H(F) alloys

The optoelectronic properties of a-Si, Ge:H(F) alloys

Photo-created defects in a-Si:H as elucidated by ESR, LESR and CPM

Photo-created defects in a-Si:H as elucidated by ESR, LESR and CPM

Comparative study of the incorporation scheme of H in a-Si:H alloyed with C, N and O

Comparative study of the incorporation scheme of H in a-Si:H alloyed with C, N and O

Defect Frozen Phenomena in Phosphorus-Doped Hydrogenated Amorphous Silicon

Defect frozen phenomenon in hydrogenated amorphous silicon (a-Si: H) was investigated with studying temperature dependence of dc conductivity and excess heat capacity in samples which were cooled at various cooling rates from a thermal equilibrium state kept at 250°C for 1h. Differential scanning calorimetry (DSC) studies of P-doped a-Si: H show the behavior governed by relaxation of defect frozen state which is characterized by the equilibrium temperature TE. The TE detected by DSC agrees with the one determined by the temperature dependence of dc conductivity. The temperature dependence of excess heat capacity is successfully interpreted by a simulation based on the model of defect specific heat which is caused by the relaxation process of defect frozen states. The temperature dependence of dc conductivity above TE is characterized by the activation energy Ea. The experimental relation between TE and Ea in P-doped and compensated a-Si: H was discussed semi-quantitatively on the basis of a model for frozen defect states. It is suggested that a large amount of D0 (neutral dangling bond state) in the compensated sample plays an important role in the relaxation phenomena of defect frozen states.

Optical modulation spectroscopy in a-Si:H at room temperature

Optical modulation spectroscopy in a-Si:H at room temperature

Laser-induced chemical vapor deposition of hydrogenated amorphous silicon: Photovoltaic devices and material properties

Laser-induced chemical vapor deposition of hydrogenated amorphous silicon: Photovoltaic devices and material properties

Photothermal and photoconductive determination of surface and bulk defect densities in amorphous silicon films

The sub-band-gap optical absorption spectra of high-quality hydrogenated amorphous silicon (a-Si:H) films are shown to be dominated by surface and interface state absorption when measured by photothermal deflection spectroscopy (PDS), while spectra determined using the constant photocurrent method (CPM) are not. For bulk defect states (both as-deposited and light-induced), the integrated subgap absorption is approximately twice as large for PDS as for CPM. Similarly, the conversion factor relating integrated subgap absorption with neutral dangling bond density is twice as large for CPM as PDS. This factor of 2 results from CPM seeing only transitions from below midgap into the conduction band while PDS sees transitions from the valence band into states above midgap as well.

Transient photocurrent saturation and deep trapping in hydrogenated amorphous silicon

Transient photocurrent saturation and deep trapping in hydrogenated amorphous silicon

Properties of the Interface Between Amorphous Silicon and Nitride

ABSTRACTThe structural, compositional and electronic properties of the a-Si:H/a-SiNx:H interface are reported. High resolution TEM and light/dark ESR studies conclude that the interface has a finite width of the order of 10 Å. In addition, there is a high density of charges residing near the interface. Band bendings occur in both a-Si:H and a-SiNx:H, resulting in few neutral dangling bonds in the a-Si:H/a-SiNx:H multilayer structure. The depletion width in the nitride is of the order of 100 Å. The slow decay of the LESR in multilayers with thin sublayers is attributed to charges trapped in the slow states in the nitride.

The Dangling Bond in Undoped Amorphous Hydrogenated Silicon: Trap or Recombination Center?

ABSTRACTThe role of the neutral dangling bond defect upon photocarrier processes in undoped amorphous hydrogenated silicon (a-Si:H) is discussed. The evidence that the dangling bond is a simple recombination center is reviewed, and it is shown that this model does not account for photocurrent response time measurements. Experimental data pertinent to the role of electrical contacts upon response time measurements are presented, and it is concluded that contact effects do not account for response-time measurements. The possibility that the dangling bond is primarily an electron trap is discussed.

Photoconductivity and photoluminescence and their relation to light-induced ESR in (Ge0·42S0·58)1−x(Sb0·4S0·6)x glasses

Abstract Photoconductivity, photoluminescence and light-induced ESR have been observed in (Ge0·42S0·58)1−x(Sb0·4S0·6)x glasses. The photoconductivity decays rapidly immediately after the illumination is switched off, with no appreciable decrease in the photoinduced ESR signal, and then decays linearly with a decrease in the ESR signal. This decrease provides evidence that the metastable neutral dangling bonds act as the limiting process of the photoconductivity. The fatigue of the photoluminescence and the increase in the light-induced ESR originate from the same defect centre in Ge0·42S0·58 consistent with the Street-Mott model.

Photoconductivity of Boron Doped A—SiN X:H

AbstractThe photoconductivity of boron doped a—SiNx:H(x=O.07)has been studied by steady state secondary photocurrent, xerographic photodischarge, the time of flight measurement, and ESR. The dominant carrier of the photocurrent in a—SiNx:H is found to be electron. The μτ product of the electron decreases with increasirg doping amount of boron, while that of the hole increases and becomes largerthan 10-8cm2/V. From these results it is found that the life time of the hole becomes longer with increasing the amount of doping boron. The intensity of the ESR signal due to the neutral dangling bonds decreases monotonically with doping boron, and this decrease of the neutral dangling bond density is considered to be due to not only change of the occupation statistics, but mainly to the chemical or electrical interaction between boron and nitrogen.