Showing papers on "Amorphous silicon published in 1987"
PARC1
TL;DR: In this paper, it was shown that the stretched-exponential relaxation commonly observed in disordered systems is explained by time-dependent atomic diffusion, and a quantitative relation between the relaxation and the diffusion was established.
Abstract: In this paper we find that the stretched-exponential relaxation commonly observed in disordered systems is explained by time-dependent atomic diffusion. The relaxation is observed in the electronic properties of hydrogenated amorphous silicon (a-Si:H), a ``hydrogen glass'' material, and reflects the equlibration of localized electronic states. The relaxation is attributed to the motion of bonded hydrogen which exhibits dispersive diffusion with a characteristic power-law time dependence. A quantitative relation between the relaxation and the diffusion is established.
500 citations
428 citations
PARC1
TL;DR: Substitutional doping of hydrogenated amorphous silicon and germanium with phosphorus, arsenic, and boron with use of electron-spin-resonance techniques, optical absorption, and transport measurements and experimental evidence for the existence of exchange-coupled electron-hole pairs in compensated a-Si:H is presented.
Abstract: Substitutional doping of hydrogenated amorphous silicon (a-Si:H) and germanium (a-Ge:H) with phosphorus, arsenic, and boron has been investigated, with use of electron-spin-resonance techniques, optical absorption, and transport measurements. Doping-induced changes in the density of shallow states and deep defects (dangling bonds) are compared for the different doping-host systems. Hyperfine spectra of neutral donor levels are observed in spin resonance and used to deduce a microscopic picture of the underlying donor wave functions. Based on the dependence of the occupancy of deep and shallow states on doping levels and temperature, a detailed model for the electronic density of states in n-type a-Si:H and a-Ge:H below the conduction-band mobility edge is obtained. Furthermore, similar studies in nominally compensated a-Si:H are used to discuss the location of boron acceptor states in this material as well as questions concerning light-induced creation of metastable dangling bonds. Experimental evidence for the existence of exchange-coupled electron-hole pairs in compensated a-Si:H is presented. For an investigation of the doping process, the incorporation of the various dopant atoms from the deposition gas phase into the amorphous film has been studied by secondary-ion mass spectroscopy. The concentration of electronically active dopants in the deposited film is related to the totalmore » concentrations of dopants in the solid or the deposition gas phase for a calculation of the corresponding doping efficiencies.« less
228 citations
TL;DR: In this article, bias dependence of the threshold voltage shift in a series of amorphous silicon-silicon nitride thin-film transistors was measured, where the composition of the nitride is varied.
Abstract: We have measured the bias dependence of the threshold voltage shift in a series of amorphous silicon‐silicon nitride thin‐film transistors, where the composition of the nitride is varied. There are two distinct instability mechanisms: a slow increase in the density of metastable fast states and charge trapping in slow states. State creation dominates at low fields and charge trapping dominates at higher fields. The state creation is found to be independent of the nitride composition, whereas the charge trapping depends strongly on the nitride composition. This is taken as good evidence that state creation takes place in the hydrogenated amorphous silicon (a‐Si:H) layer, whereas the charge trapping takes place in the a‐SiN:H. The metastable states are suggested to be Si dangling bonds in the a‐Si:H, and the state creation process similar to the Staebler–Wronski effect. The confirmation of state creation in a thin‐film transistor means that states can be created simply by populating conduction‐band states i...
202 citations
TL;DR: In this article, the effect of plasma excitation frequency on the deposition rate and on the optical and electrical properties of amorphous silicon film was studied over the range 25-150 MHz.
Abstract: The effect of plasma excitation frequency on the deposition rate and on the optical and electrical properties of amorphous silicon film is studied over the range 25–150 MHz. Deposition rates as high as 21 A/sec are obtained at ∼70 MHz, which is a factor of 5–8 larger than typical rates obtained for the conventional 13.56-MHz silane glow-discharge system. Only minor changes occur in the defect density (as measured by the photothermal deflection spectroscopy method), the optical bandgap, and the electrical conductivity over this frequency range. In a preliminaryinterpretation given here, the large variation of the deposition rate as a function of excitation frequency is explained in terms of changes in the electron energy distribution function.
181 citations
TL;DR: In this article, bias stress measurements on amorphous silicon-silicon nitride ambipolar thin-film transistors give clear evidence for the coexistence of two distinct instability mechanisms: the metastable creation of states in the a−Si:H layer and charge trapping in a•SiN:Hlayer.
Abstract: Bias stress measurements on amorphous silicon‐silicon nitride ambipolar thin‐film transistors give clear evidence for the co‐existence of two distinct instability mechanisms: the metastable creation of states in the a‐Si:H layer and charge trapping in the a‐SiN:H layer. The creation of metastable states in the a‐Si:H is found to dominate at low positive bias, while charge trapping in the nitride dominates at larger positive bias and negative bias.
179 citations
158 citations
TL;DR: In this paper, 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.
Abstract: 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.
152 citations
01 Jan 1987-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, it was shown that both processes, epitaxial crystallization and layer-by-layer amorphization, are controlled by ion-beam induced defect production at, or near, the crystalline/amorphous interface.
Abstract: Thin amorphous silicon layers can be produced in crystalline silicon substrates by ion-implantation. Subsequent ion-irradiation at elevated temperatures can induce such layers to either crystallize epitaxially or increase in thickness, layer by layer. This paper examines these processes and their dependence on substrate temperature and ion-irradiation parameters. It is shown that both processes, epitaxial crystallization and layer-by-layer amorphization, are controlled by ion-beam induced defect production at, or near, the crystalline/amorphous interface. The competition between defect production (determined by the ion flux and rate of nuclear energy deposition) and dynamic defect annealing (determined by the substrate temperature) is shown to play an important role in determining whether the layer crystallizes or amorphizes. Possible models for the observed behavior are discussed.
147 citations
TL;DR: The theory underlying the steady-state photocarrier grating technique, including the effect of surface recombination, is presented in this paper, where the diffusion lengths ranging from 200 A to 10 μm can be measured with an accuracy of better than 5%.
Abstract: The theory underlying the steady‐state photocarrier grating technique is presented, including the effect of surface recombination. Experimental results for amorphous hydrogenated silicon and semi‐insulating GaAs prove that diffusion lengths ranging from 200 A to 10 μm can be measured with an accuracy of better than 5%.
145 citations
TL;DR: In this paper, a microscopic model based on charge-induced breaking of weak Si-Si bonds is proposed as an explanation for the experimentally observed increase of the dangling-bond density in a-Si: H upon illumination, charge injection, and doping.
Abstract: A microscopic model based on charge-induced breaking of weak Si-Si bonds is proposed as an explanation for the experimentally observed increase of the dangling-bond density in a-Si: H upon illumination, charge injection, and doping. Energetic aspects of the conversion between weak and dangling bonds and implications for the electronic density of states of a-Si: H are described, and the relation of the model to negative4 defects in this material is discussed.
TL;DR: In this paper, the performance of thin-film transistors was found to depend upon the deposition temperature of the transistors, and low threshold voltages and effective mobilities as high as 32 cm2/V.s were reported for devices fabricated in 150-nm-thick films with maximum processing temperature of 860°C.
Abstract: Thin-film transistors (TFT's) were fabricated in low-temperature (550°C) crystallized amorphous LPCVD silicon films. The performance of these devices was found to depend upon the deposition temperature. Low threshold voltages and effective mobilities as high as 32 cm2/V.s are reported for devices fabricated in 150-nm-thick films with maximum processing temperature of 860°C. The performance of these devices is shown to be far superior to devices fabricated in as-deposited polycrystalline silicon films.
TL;DR: In this article, the growth process of a-Si:H films via the glow-discharge decomposition of SiH 4, and its relationship to structural, optical and electronic properties of the deposited films are discussed.
TL;DR: In this article, the amount of amorphous silicon microstructure and its degree of passivation by hydrogen were quantified using infrared measurements. And the photoconductivities of ammorphous silicon (a•Si:H), amorphus silicon carbon (a·SiC:H) and amorphosilicon germanium (a.SiGe:H).
Abstract: We introduce a parameter obtained from infrared measurements as a means of quantifying the amount of amorphous silicon microstructure and its degree of passivation by hydrogen. Using this parameter, the photoconductivities of amorphous silicon (a‐Si:H), amorphous silicon carbon (a‐SiC:H), and amorphous silicon germanium (a‐SiGe:H) fall on the same curve. We discuss the relevance of these results with regard to material quality.
TL;DR: In this paper, the amorphous, random structure of these ceramics is investigated and it is shown that excess C, present in all compositions studied, appears to be present as very small polyaromatic crystallites, resembling pyrolytic carbon in structure.
Abstract: Ceramics fibers in the system Si-C-N-O prepared by pyrolysis of melt-spun, cured, amorphous organosilicon polymers have a predominantly amorphous chemical structure, consisting of carbon, nitrogen, and oxygen bonds to silicon. These amorphous silicon oxycarbonitrides have chemical bonding approach a random distribution: i.e. individual silicon atoms are simultaneously bonded to C, N, and O in a random fashion. Such structures have not been characterized previously. Excess C, present in all compositions studied, appears to be present as very small polyaromatic crystallites ({approx} 4 nm domain size in the aromatic plane) resembling pyrolytic carbon in structure. This carbon is highly resistant to oxidation. The amorphous, random structure of these ceramics is a consequence of small-scale elemental homogeneity in the amorphous polymer precursor and of insufficient thermal energy during pyrolysis to promote crystallization.
TL;DR: In this article, surface reactions of SiH3 on hydrogenated amorphous silicon (a•Si:H) were studied in a parallel plate reactor, combined with measurements of surface reflection coefficient, spatial density profile, and a•Si deposition rate, and the reaction probability varied from 0.1 up to 0.2 in the 40-350°C temperature domain.
Abstract: Mercury photosensitized decomposition of SiH4 is used to study surface reactions of SiH3 on hydrogenated amorphous silicon (a‐Si:H). The method involves modeling of gas phase production, reaction and diffusion to the walls of reactive species, in a parallel plate reactor, combined with measurements of surface reflection coefficient of SiH3, spatial density profile of SiH3, and a‐Si:H deposition rate. The reaction probability of SiH3 on a‐Si:H varies from 0.1 up to 0.2 in the 40–350 °C temperature domain. However, a large fraction (≥60%) of adsorbed SiH3 recombine on the surface, instead of being incorporated in the film.
TL;DR: In this paper, the authors measured energy-band discontinuities for hydrogenated amorphous silicon and crystalline silicon heterojunctions by internal photoemission, and they found that the band discontinuity mainly exists at the valence-band side.
Abstract: Energy‐band discontinuities were measured for hydrogenated amorphous silicon and crystalline silicon heterojunctions by internal photoemission. The measurement was performed both for the conduction‐band side and for the valence‐band side, and the conduction‐band discontinuity and the valence‐band discontinuity were estimated to be 0.09 and 0.71 eV, respectively. This result indicates that the band discontinuity mainly exists at the valence‐band side.
TL;DR: Amorphous-silicon states have been generated in a computationally efficient manner by quenching liquid silicon configurations using a molecular-dynamics simulation using two-and three-body interatomic Si potentials as discussed by the authors.
Abstract: Amorphous-silicon states have been generated in a computationally efficient manner by quenching liquid silicon configurations using a molecular-dynamics simulation. Classical two- and three-body interatomic Si potentials have been used. We present results for the radial distribution functions, bond-angle distributions, vibrational densities of states, and neutron scattering functions for the theoretically generated a-Si states. The molecular-dynamics simulations generate threefold- and fivefold-coordinated defects in the a-Si structures.
TL;DR: In this paper, the optical gap of undoped hydrogenated amorphous silicon (a-Si: H) was investigated as a function of the ambient temperature, the deposition temperature and the post-annealing temperature using photoacoustic spectroscopy.
Abstract: Optical absorption spectra of undoped hydrogenated amorphous silicon (a-Si: H) were investigated as a function of the ambient temperature, the deposition temperature and the post-annealing temperature using photoacoustic spectroscopy. On the basis of the temperature dependence of the photoacoustic signal, the optical gap and the characteristic energy of the exponential tail have been discussed in relation to the thermal and structural disorder. From the dependence of the optical absorption spectra on the deposition as well as post-annealing temperature, the optical gap of a-Si: H has been found to be mainly affected by the bonded hydrogen content rather than structural disorder. A weak absorption band overlapping the absorption tail has been well correlated with a spin density of electron spin resonance (ESR) signals (g = 2.0055), namely, a density of singly occupied dangling bonds. It has been demonstrated that the structural disorder and a number of defect states are not so much affected by pos...
Book•
01 May 1987
TL;DR: In this article, the basic operating principles and design of solar cells based on crystalline material, and the technology used to produce cells are discussed. But the development of the promising new technology of amorphous silicon solar cells is not discussed.
Abstract: This book offers a treatment of the development of the promising new technology of amorphous silicon solar cells. It reviews the basic operating principles and design of solar cells based on crystalline material, and the technology used to produce cells. It then delves into the fundamental physics of amorphous semiconductors relating to the device physics of amorphous silicon solar cells.
TL;DR: In this article, the equilibrium temperature for intrinsic glow discharge amorphous silicon was found to be 195-200°C and the defect left behind after fast cooling resulted in a temperature-dependent dc photoconductivity.
Abstract: We find the equilibrium temperature for intrinsic glow discharge amorphous silicon to be 195–200 °C. Defects left behind after fast cooling result in a temperature‐dependent dc photoconductivity which shows small differences in the tail state recombination kinetics when compared to defects left behind in the same number after light soaking. Finally anneal kinetics of fast cool defects follow neither singly activated, mono‐, nor bimolecular kinetics with a temperature dependence indicating activation energies from 1.0 to 1.4 eV. Unlike the distribution of defects left behind in similar number as a result of light soaking at room temperature, the distribution of defects resulting from fast cooling from higher temperature is shifted to higher energies and requires much longer anneal times.
TL;DR: Tin oxide films were prepared by electron beam evaporation of pellets of Specpure SnO2 in the presence of added oxygen as mentioned in this paper, and by optimizing the deposition conditions, transparent and conducting tin oxide films exhibiting the structural characteristics of a predominant SnO 2 phase were produced.
TL;DR: In this article, a systematic deposition of hydrogenated amorphous silicon films from pure SiH4 plasma was made in a capacitively coupled rf glow discharge system by changing anode-cathode spacing d and chamber pressure p simultaneously.
Abstract: A systematic deposition of hydrogenated amorphous silicon films from pure SiH4 plasma was made in a capacitively coupled rf glow‐discharge system by changing anode–cathode spacing d and chamber pressure p simultaneously. The data of the deposition rate in the p‐vs‐d space had two boundaries. One was pd=const. The other seems to be pd2=const. The rf plasma can stably sustain between the boundaries. The boundaries are discussed with rf power per SiH4 molecule and with overlapping Paschen’s lines of various fragments, especially H2 due to the SiH4 dissociation. We found the optimum conditions in which the deposition rate was more than 10 A/s without large photo‐induced degradation. 10% efficient p‐i‐n solar cells were achieved with the intrinsic layer deposition rate of 3.9 A/s and more than 6% efficiency with 10 A/s.
TL;DR: In silicon, evidence for a new dissipation mechanism at low temperatures is found and the first observation of a saturation with strain of the resonant contribution to the sound velocity is reported.
Abstract: Using the high-Q mechanical-oscillator technique we have measured the sound velocity and mechanical dissipation of high-purity single-crystal silicon as functions of temperature (0.005--4.2 K), frequency (0.6--6.0 kHz), and strain amplitude (${10}^{\mathrm{\ensuremath{-}}5}$--${10}^{\mathrm{\ensuremath{-}}8}$). In the mechanical properties we find a surprisingly strong temperature dependence with the same qualitative behavior for silicon as for vitreous silica. This implies a density of two-level systems only 2 orders of magnitude lower for silicon than amorphous silica. In silicon we find evidence for a new dissipation mechanism at low temperatures and report the first observation of a saturation with strain of the resonant contribution to the sound velocity.
ENEA1
TL;DR: Electron-beam irradiation is shown to induce room-temperature polycrystalline nucleation in the amorphous layer and such a process becomes competitive with solid-phase epitaxy for a dose higher than 5\ifmmode\times\texttimes\fi{}${10}^{5}$ C/${\mathrm{cm}}^{2}$.
Abstract: The technique of cross-sectional electron microscopy has been used to investigate the mechanism of electron-beam-induced solid-phase epitaxy of amorphous silicon at room temperature. Cross sections of samples with surface and buried amorphous layers were irradiated in a transmission electron microscope with electrons of energies higher than the threshold energy for atomic displacement and the induced recrystallization process was characterized. Evidence is given that the dominant mechanism of recrystallization is the diffusion to the amorphous-crystalline interface of the defects produced by elastic displacements both in the crystalline and in the amorphous region. The diffusion length of such defects results in the order of 25--30 nm and is approximatively the same in the crystalline and amorphous Si. Electron-beam irradiation is shown to induce room-temperature polycrystalline nucleation in the amorphous layer. Such a process becomes competitive with solid-phase epitaxy for a dose higher than 5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ C/${\mathrm{cm}}^{2}$.
Patent•
28 Oct 1987TL;DR: In this paper, the authors improved the sensitivity of the CaAlAs diode laser by using a triple-layer structure consisting of an upper layer (33) made of amorphous silicon containing germanium and carbon incorporated thereinto, a middle layer (32), made of polysilicon, and a lower layer (31) consisting of a barrier layer.
Abstract: The photoconductive layer (3) has a triple-layer structure comprised of an upper layer (33) made of amorphous silicon containing germanium and carbon incorporated thereinto, a middle layer (32) made of amorphous silicon containing germanium incorporated thereinto, and a lower layer (31) made of amorphous silicon. The upper layer (33) formed between a surface layer (4) and the middle layer (32), and the lower layer (31) formed between the middle layer (32) and a barrier layer (2) serve to reduce the energy difference and the interfacial state between respective two layers respectively. High electrophotographic sensitivity for a longer wavelength light can be obtained. The sensitivity in the oscillation wavelength of the CaAlAs diode laser is improved.
TL;DR: An amorphous silicon photoconductor has been demonstrated in a reflection mode nematic field effect liquid crystal spatial light modulator and the performance characteristics as well as a theoretical model for the device are reported.
Abstract: An amorphous silicon photoconductor has been demonstrated in a reflection mode nematic field effect liquid crystal spatial light modulator. The thin-film photoconductor provided high resolution of >35 lp/mm and sensitivity better than 20 microW/cm(2). In addition the switching speed was liquid crystal limited. Reported are the performance characteristics as well as a theoretical model for the device.
TL;DR: The structural and electronic properties of the complex tetrahedral structures B-8 and T-12 phases of silicon and carbon are computed with ab initio density-functional calculations of the energy, pressure, and enthalpy.
Abstract: The structural and electronic properties of the complex tetrahedral structures B-8 (or ``BC8,'' bcc with 8 atoms per cell) and T-12 (or ``ST12,'' simple tetragonal with 12 atoms per cell) phases of silicon and carbon are computed with ab initio density-functional calculations of the energy, pressure, and enthalpy. For silicon, the B-8 and T-12 phases are found to be metastable, consistent with their formation during pressure reduction in high-pressure experiments. Energies of both structures are close to that of amorphous silicon. T-12 has an indirect gap larger than diamond-structure Si whereas B-8 is semimetallic. For carbon, the B-8 phase is found to be stable, relative to diamond and all previously calculated metallic phases, above pressures of 12 Mbar. This represents a new limit for the stability of diamond.