Picosecond Photocarrier Lifetimes in Ion-Irradiated Amorphous and Crystalline Silicon

1991 ◽  
Vol 235 ◽  
Author(s):  
P. A. Stolk ◽  
L. Calcagnile ◽  
S. Roorda ◽  
H. B. van Linden ◽  
Van den Heuvell ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Liquid Nitrogen ◽  
Crystalline Silicon ◽  
Defect Density ◽  
Liquid Nitrogen Temperature ◽  
Generation Rate ◽  
Structural Defects ◽  
Pump Probe ◽  
Recombination Centers

ABSTRACTCrystalline silicon (c-Si) and structurally relaxed amorphous silicon (a-Si) were implanted with 1 MeV Si+ at liquid nitrogen temperature. The photocarrier lifetime τ in the implanted samples was determined with sub-picosecond resolution through pump-probe reflectivity measurements. At low damage levels (i.e. <1014 ions/cm2), τ decreases with increasing ion dose in both materials, indicating a build up of trapping and recombination centers. The dominant centers in c-Si appear to be related to simple defects. The generation rate of electrically active defects is found to be the same in relaxed a-Si and c-Si, which suggests that the structural defects formed in a-Si strongly resemble the simple defects in c-Si. For ion doses > 1014 /cm2, τ saturates at a level of 0.8 ps for both materials. Strikingly, the saturation sets in far below the dose needed to amorphize (>1015 /cm2). The defect density in a-Si at saturation is estimated to be ≈1.6 at.%.

Metastable Defects in Tritiated Amorphous Silicon

2007 ◽  
Vol 989 ◽  
Author(s):  
Tong Ju ◽  
Janica Whitaker ◽  
Stefan Zukotynski ◽  
Nazir Kherani ◽  
P. Craig Taylor ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Liquid Nitrogen ◽  
Beta Decay ◽  
Defect Density ◽  
Average Energy ◽  
Liquid Nitrogen Temperature ◽  
Beta Particle ◽  
Dangling Bond ◽  
Staebler Wronski Effect ◽  
Induced Defects

AbstractThe appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to 3He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half âlife of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 1016 to 1017 /cm3 , which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3x1019/cm3 after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2x1020/cm3). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200°C, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150°C, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.

Saturation behavior of the Light-Induced Defect Density in Hydrogenated Amorphous Silicon

1990 ◽  
Vol 192 ◽  
Author(s):  
H. R. Park ◽  
J. Z. Liu ◽  
P. Roca i Cabarrocas ◽  
A. Maruyama ◽  
M. Isomura ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Room Temperature ◽  
Urbach Energy ◽  
Defect Density ◽  
Generation Rate ◽  
Carrier Generation ◽  
Defect Generation ◽  
Ion Laser ◽  
Hydrogenated Amorphous ◽  
Defect Densities

ABSTRACTUsing a Kr ion laser (λ = 647.1 nm) to produce a carrier generation rate G of 3 × 1020 cm−3s−1, we have saturated the light-induced defect generation in hydrogenated (and fluorinated) amorphous silicon (a-Si:H(F)), within a few hours near room temperature. While the defect generation rate scales roughly with 1/G2, the saturation defect densities Ns,sat are essentially independent of G. The saturation is not due to thermal annealing. We have further measured Ns,sat m 37 a-Si:H(F) films grown in six different reactors under different conditions. The results show that Ns,sat lies between 5 × 1016 and 2 × 1017 cm−3, that Ns,sat drops with decreasing optical gap and hydrogen content, and that Ns,sat is not correlated with the initial defect density or with the Urbach energy.

Effect of Deposition-Induced Annealable Defects on Light-Induced Defect Generation in a-Si:H

1993 ◽  
Vol 297 ◽  
Author(s):  
Jong-Hwan Yoon
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Generation Rate ◽  
Defect Generation ◽  
Saturated State ◽  
Microscopic Models ◽  
Hydrogenated Amorphous ◽  
Substrate Temperatures

In this paper we present a method to determine the annealable defect density(ΔNann) present in hydrogenated amorphous silicon(a-Si:H). The effects of the annealable defects on the light-induced defect generation rate, saturated defect density (Nsat) and the change of defect density in the light-induced saturated state(ΔNsat) have been studied. Annealable defect density was varied by depositing samples at various substrate temperatures or by post-growth anneals of samples grown at low substrate temperatures. It is found that the generation rate, N satand ΔNsat are well correlated with ΔNann. In particular, the ΔNsat is found to follow a relation ΔNsat ≈ ΔNann. These results suggest that defect-related microscopic models are appropriate for light-induced metastability.

Structural Relaxation of Vacancies in Amorphous Silicon

1997 ◽  
Vol 467 ◽  
Author(s):  
Eunja Kim ◽  
Young Hee Lee ◽  
Changfeng Chen ◽  
Tao Pang
Keyword(s):  
Amorphous Silicon ◽  
Structural Relaxation ◽  
Crystalline Silicon ◽  
Defect Density ◽  
Tight Binding ◽  
Unusual Behavior ◽  
High Defect Density ◽  
Significant Difference ◽  
Gap States ◽  
Dynamics Method

ABSTRACTWe have studied the structural relaxation of vacancies in amorphous silicon (a-Si) using a tight-binding molecular-dynamics method. The most significant difference between vacancies in a-Si and those in crystalline silicon (c-Si) is that the deep gap states do not show up in a-Si. This difference is explained through the unusual behavior of the structural relaxation near the vacancies in a-Si, which enhances the sp2 + p bonding near the band edges. We have also observed that the vacancies do not migrate below 450 K although some of them can still be annihilated, particularly at high defect density due to large structural relaxation.

Structural Defects in Amorphous Silicon Probed by Sub-Picosecond Photocarrier Dynamics

1990 ◽  
Vol 205 ◽  
Author(s):  
P.A. Stolk ◽  
S. Roorda ◽  
L. Calcagnile ◽  
W.C. Sinke ◽  
H.B. Van Linden Van Den Heuvell ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Decay Time ◽  
Auger Recombination ◽  
Photogenerated Electron ◽  
High Plasma ◽  
Structural Defects ◽  
Lower Plasma ◽  
Electron Hole ◽  
Pump Probe ◽  
Electron Hole Plasma

AbstractThe dynamics of a photogenerated electron-hole plasma in pure amorphous silicon (a-Si) in different stages of structural relaxation have been studied with sub-picosecond resolution using pump-probe reflectivity measurements. For high plasma densities (> 1020/cm3) the plasma evolution is dominated by Auger recombination. At lower plasma densities (≈ 1018/cm3) the plasma decays exponentially with a time constant τ, suggesting that carrier trapping dominates in this regime. The decay time τ increases with the temperature at which the a-Si has been annealed, ranging from τ = 1 ps for as-implanted a-Si to τ=14 ps for a-Si annealed at 500 °C. This observation is consistent with a reduction in the number of defects in a-Si upon thermal annealing.

Recombination Process in the As-Deposited State of Hydrogenated Amorphous Silicon

1993 ◽  
Vol 297 ◽  
Author(s):  
Jong-Hwan Yoon
Keyword(s):  
Amorphous Silicon ◽  
Defect Density ◽  
Energy Levels ◽  
Hydrogenated Amorphous Silicon ◽  
Recombination Process ◽  
Defect States ◽  
Deep Defect ◽  
Recombination Centers ◽  
Hydrogenated Amorphous ◽  
Deposition Conditions

Intrinsic deep defect-related recombination process has been studied in a series of undoped hydrogenated amorphous silicon(a-Si:H) films grown under different deposition conditions. Steady-state photoconductivity (σph) was measured as a function of deep defect density Nd, Urbach energy Eu, and dark Fermi energy Ef. It was found that σph strongly depends on these parameters while Ef- stays at the energy levels lower than 0.82 eV below Ec, but it is nearly independent of those while Ef stays at above 0.82 eV. These behaviors were found to be independent of the sample deposition conditions. These results indicates that subgap defect states enclosed by E=0.82 eV and Ef are the dominant recombination centers.

Metastable Defects in Light Soaked Amorphous Silicon at 77 K

2008 ◽  
Vol 1066 ◽  
Author(s):  
Tong Ju ◽  
Paul Stradins ◽  
P. Craig Taylor
Keyword(s):  
Amorphous Silicon ◽  
Liquid Nitrogen ◽  
Room Temperature ◽  
Defect Density ◽  
One Year

ABSTRACTWe have observed the growth of defects caused by optical illumination in liquid nitrogen. We kept the sample in liquid nitrogen over one year. After one year and half the ESR signal reached ∼1018 cm−3 with no evidence of saturation. After that, we step-wise annealed isochronal the sample up to room temperature, where two thirds of original defects were annealed out. After room temperature, the sample was annealing isothermally around 300 K for several months. At this temperature, the defects slowly anneal. After a hundred of hours at 295K, the defect density decreased 10x from its original value at 77K.

Electron Probe Microanalysis of Frozen Hydrated Kidneys, Isolated Cells, and Cultured Cells

1982 ◽  
Vol 40 ◽  
pp. 402-403 ◽  
Author(s):  
Claude Lechene
Keyword(s):  
Liquid Nitrogen ◽  
Electron Probe Microanalysis ◽  
Electron Probe ◽  
Cultured Cells ◽  
Liquid Nitrogen Temperature ◽  
Elemental Content ◽  
Isolated Cells ◽  
Renal Tubular Cells ◽  
Diamond Saw ◽  
Saw Blade

Electron probe microanalysis of frozen hydrated kidneysThe goal of the method is to measure on the same preparation the chemical elemental content of the renal luminal tubular fluid and of the surrounding renal tubular cells. The following method has been developed. Rat kidneys are quenched in solid nitrogen. They are trimmed under liquid nitrogen and mounted in a copper holder using a conductive medium. Under liquid nitrogen, a flat surface is exposed by sawing with a diamond saw blade at constant speed and constant pressure using a custom-built cryosaw. Transfer into the electron probe column (Cameca, MBX) is made using a simple transfer device maintaining the sample under liquid nitrogen in an interlock chamber mounted on the electron probe column. After the liquid nitrogen is evaporated by creating a vacuum, the sample is pushed into the special stage of the instrument. The sample is maintained at close to liquid nitrogen temperature by circulation of liquid nitrogen in the special stage.

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