Conditions preventing thermal breakdown in semiconductor devices

We present results facilitating the prediction of the possibility of thermal breakdown in semiconductor devices and selection of the working parameters preventing such breakdowns.     

Undamped self-oscillations in a compensated semiconductor under conditions of impurity breakdown in the presence of a magnetic field

Conditions for the generation of undamped self-oscillations in a compensated semiconductor in the presence of a magnetic field are studied. Pis’ma Zh. Tekh. Fiz. 23, 62–66 (August 26, 1997)     

Flexural vibrations of semiconductor wafers in the presence of a pulsed thermal excitation source

An analysis is made of the action of current pulses on a metal film lying on a semiconductor wafer. It is shown that the passage of current pulses of amplitude (1–7)×10¹⁰ A/m² and duration 50–200 μs across aluminum tracks excites sound. Experimental dependences of the energy of the flexural vibrations as a function of the duration and amplitude of the pulsed action were obtained. It was observed for the first time that the melting of a metal-semiconductor contact is accompanied by an abrupt increase in the energy of the flexural vibrations of the wafer. Pis’ma Zh. Tekh. Fiz. 25, 57–63 (March 12, 1999)     

Laser-induced breakdown spectrometry as a multimetal continuous-emission monitor

Laser-induced breakdown spectrometry (LIBS) has been used to detect atomic and molecular species in various environments. LIBS has the capability to be used as a continuous-emission monitor to monitor toxic-metal concentrations in stack emissions. Recently a mobile LIBS system was calibrated in our laboratory and tested as a multimetal continuous-emission monitor during a joint U.S. Department of Energy-Environmental Protection Agency (EPA) test. LIBS measurements were performed with three sets of metal concentrations at the EPA Rotary Kiln Incinerator Simulator. The LIBS system successfully measured concentrations of Cr, Pb, Cd, and Be in near real time in this test. Real-time LIBS data were averaged and compared with data obtained from an EPA reference method that was conducted concurrently with LIBS. The details of the LIBS calibration and results of these LIBS measurements are described.     

Statistics of mesoplasma channel formation upon thermal breakdown stabilization in thin semiconductor films

A phenomenological model of the development of thermal breakdown in semiconductor films is considered, and it is shown that the average number of mesoplasma channels experimentally observed in the regime of thermal breakdown stabilization can substantially vary. The probability distribution function for the number of such luminous channels arising as a result of thermal fluctuations in a thin semiconductor film is calculated within the framework of a simple approximation.     

Laser-induced collective effects in glassy semiconductor films

Photoinduced variations in the structure of glassy semiconductor films are considered from the standpoint of the theory of self-organization, including the formation of dissipative structures and their subsequent transformation under laser irradiation, which drives the system to the new state with minimum dissipated energy of the external mechanical field. Direct experimental evidence for the existence of cooperative (synergetic) self-organization processes is provided by the results of cyclic nanoindentation measurements in films of a chalcogenide glass with As₂Se₃ stoichiometric composition exposed to band-gap light (hv ≥ E _g)).     

Laser-induced breakdown spectroscopy of molten aluminum alloy

We have demonstrated that a fiber-optic laser-induced breakdown spectroscopy (LIBS) probe is suitable for measuring the concentration of minor constituents of a molten Al alloy in a laboratory furnace. For the first time to our knowledge we are able to record the LIBS spectra in several spectral regions of seven different molten Al alloy samples by inserting the LIBS probe inside the molten alloys, allowing us to obtain a ratio calibration curve for minor constituents (Cr, Mg, Zn, Cu, Si, etc.), using Fe as a reference element. A ratio calibration curve for Fe with a major element (Al) can also be obtained with which the concentration of Fe in the alloy can be determined. The effects of the surrounding atmosphere on the LIBS spectra of the molten alloy were investigated. Effects of focal length of the lens on the LIBS signals were also studied. LIBS spectra of a solid Al alloy recorded with the same LIBS probe were compared with the LIBS spectra of the molten alloy. Our results suggest that the LIBS probe is useful for monitoring the elemental composition of an Al melt in an industrial furnace at different depths and different positions inside the melt.     

Laser-induced breakdown spectroscopy analysis of energetic materials

A number of energetic materials and explosives have been studied by laser-induced breakdown spectroscopy (LIBS). They include black powder, neat explosives such as TNT, PETN, HMX, and RDX (in various forms), propellants such as M43 and JA2, and military explosives such as C4 and LX-14. Each of these materials gives a unique spectrum, and generally the spectra are reproducible shot to shot. We observed that the laser-produced microplasma did not initiate any of the energetic materials studied. Extensive studies of black powder and its ingredients by use of a reference spectral library have demonstrated excellent accuracy for unknown identification. Finally, we observed that these nitrogen- and oxygen-rich materials yield LIBS spectra in air that have correspondingly different O:N peak ratios compared with air. This difference can help in the detection and identification of such energetic materials.     

Laser-induced breakdown spectroscopy of alkali metals in high-temperature gas

Laser-induced breakdown spectroscopy (LIBS) measurements of alkali in the high-temperature exhaust of a glass furnace show an attenuation of the Na and K LIBS signals that correlates with the stoichiometry of the bath gas surrounding the spark. The results are explained as being due to (1) a strong increase in the concentration of atomic Na and K, resulting in neutral line signal absorption by these atoms, and to (2) a change of phase of the major Na- and K-containing species from an aerosol to a gaseous phase when the gas mixture becomes fuel rich, resulting in a reduced LIBS emission intensity. LIBS sampling at lower temperatures, or in a consistently oxidizing environment, or both are suggested strategies for circumventing these difficulties.     

Laser-induced breakdown spectroscopy of high-pressure bulk aqueous solutions

Laser-induced breakdown spectroscopy (LIBS) is presented for detection of several Group I and II elements (e.g., Na, Ca, Li, and K), as well as Mn and CaOH, in bulk aqueous solution at pressures exceeding 2.76 x 10(7) Pa (276 bar). Preliminary investigations reveal only minor pressure effects on the emission intensity and line width for all elements examined. These effects are found to depend on detector timing and laser pulse energy. The results of these investigations have implications for potential applications of LIBS for in situ multi-elemental detection in deep-ocean environments.     

Laser-induced breakdown in H2 gas at 248 nm

Measurement of optical breakdown threshold in hydrogen gas with a KrF excimer laser at 248 nm is presented. The result shows a sharp increase of the threshold intensity at a few atmospheres of gas pressure when a focusing lens with a longer focal length is used. This enhancement is partially explained in terms of the influence of pump beam depletion in stimulated Raman scattering.     

Maneuvering target tracking in the presence of complicated measurement noises

Abstract

In modern radar tracking systems, measurement noise is significantly correlated when the measurement frequency is high enough. The problem of maneuvering target tracking in the presence of complicated measurement noise is considered in this paper. The measurement noise is modeled as the sum of a high‐order autoregressive process and a white process. This noise can be decorrelated by including the noise‐correlation variables in the target state. The theoretical analysis of tracking performance is derived. If some of the parameters (including the noise‐correlation parameters) are unknown, these unknown parameters can be estimated adaptively using a modified innovation correlation method. This parameter estimation method is very useful when the measurement noise can be modeled as the sum of a first‐order Markov process and a white process.     

Laser-induced breakdown spectroscopy for the detection of gunshot residues on the hands of a shooter

Laser-induced breakdown spectroscopy (LIBS) has been used to determine whether the hands of a suspected gun user contain traces of gunshot residue. Samples are obtained by pressing adhesive tape against the skin of the suspect and analyzing the tape directly. When the suspect has fired multiple shots, or if the gun has not been cleaned, the gunshot residue provides a spectral signature that is readily apparent, but a person who has fired a single shot from a clean gun is not so easy to identify. The error rates associated with the LIBS identification of a subject who fired one shot from a clean gun have been evaluated by Monte Carlo simulation techniques, and criteria are proposed for defining a positive or a negative test result.     

Laser-induced breakdown spectroscopy for analysis of chemically etched polytetrafluoroethylene

Laser-induced breakdown spectroscopy (LIBS) is used to analyze chemically etched polytetrafluoroethylene (PTFE). The elements O, F, H, and Na are determined qualitatively in the depth dimension. It is shown that O, H, and Na signals are greatest at the surface and decrease as the laser burrows through the etched layer into the bulk. In contrast, the fluorine signal is a minimum at the surface and increases with depth. The average ablation rate for PTFE under the experimental conditions is found to be 1.9 microm per pulse. Using this value, the depth of the etched layer is determined to be 8 microm. A calibration curve produced by analysis of different polymers gives mole fractions of O, F, and H at the surface of the etched PTFE of 0.2, 0.3, and 0.1, respectively.     

Laser-induced breakdown spectroscopy detection and classification of biological aerosols

Laser-induced breakdown spectroscopy (LIBS) is examined as a potential method for detecting airborne biological agents. A spectrally broadband LIBS system was used for laboratory measurements on some common biological agent simulants. These measurements were compared to those of common, naturally occurring biological aerosol components (pollen and fungal spores) to determine the potential of LIBS for discriminating biological agents from natural background aerosols. A principal components analysis illustrates that linear combinations of the detected atomic lines, which are present in different ratios in each of the samples tested, can be used to discriminate biological agent simulants from other biological matter. A more sensitive, narrowband LIBS instrument was used to demonstrate the detection of single simulant (Bg) particles in the size range 1-5 microns. Ca, Mg, and Na, which are present in varying concentrations between 0.3 and 11% (by mass) in the Bg particles, were observed in single particles using LIBS.     

Laser-induced breakdown spectrometry of titanium dioxide antireflection coatings in photovoltaic cells

Silicon photovoltaic cells have design and material requirements different from those of most other silicon electronic devices. Not only are nearly ideal silicon surfaces required, but also the bulk properties must be of uniform high quality for high-energy conversion efficiency. In this paper, emission spectra of laser-generated plasmas from titanium dioxide antireflection coatings in solar cells are reported. A pulsed nitrogen laser at 337.1 nm was used with a pulse width of 10 ns and a laser fluence of 8.6 J/cm(2) onto the sample. The plasmas were detected using a charge-coupled device. Depth profilings from several samples with different thicknesses of titanium dioxide have been studied. A method for measuring thin TiO(2) films based on the observation of such profiles was developed. The effect of the laser fluence on the sensitivity of the present method has been examined. Depth resolutions are fluence-dependent but are on the order of 40 nm. The dependence between titanium dioxide plasma intensity and material reflectivity at the laser wavelength is discussed. Another valuable aspect of the technique is the ability to perform measurements in a contactless manner at room temperature and atmospheric pressure on wafer-sized samples.     

Laser-induced breakdown spectroscopy at high temperatures in industrial boilers and furnaces

Laser-induced breakdown spectroscopy (LIBS) was applied (1) near the superheater of an electric power generation boiler burning biomass, coal, or both; (2) at the exit of a glass-melting furnace burning natural gas and oxygen; and (3) near the nose arches of two paper mill recovery boilers burning black liquor. Difficulties associated with the high temperatures and high particle loadings in these environments were surmounted by use of novel LIBS probes. Echelle and linear spectrometers coupled to intensified CCD cameras were used individually and sometimes simultaneously. Elements detected include Na, K, Ca, Mg, C, B, Si, Mn, Al, Fe, Rb, Cl, and Ti.     

Laser-induced breakdown spectroscopy for the environmental determination of total carbon and nitrogen in soils

Soils from various sites have been analysed with the laser-induced breakdown spectroscopy (LIBS) technique for total elemental determination of carbon and nitrogen. Results from LIBS have been correlated to a standard laboratory-based technique (sample combustion), and strong linear correlations were obtained for determination of carbon concentrations. The LIBES technique was used on soils before and after acid washing, and the technique appears to be useful for the determination of both organic and inorganic soil carbon. The LIBS technique has the potential to be packaged into a field-deployable instrument.     

A comparison of avalanche breakdown probabilities in semiconductor materials

Abstract

Using a hard dead space impact ionization model, the dependence of breakdown probabilities on overbias ratio in single photon avalanche diodes is investigated theoretically in a variety of semiconductor materials for the simple case of constant electric field, that is, in a p⁺-i-n⁺ diode structure. By using avalanche widths of 2 μm, the effects of dead space are minimized so that the breakdown probability results are determined primarily by the enabled ionization coefficients of the materials. The results illustrate how the slope of breakdown probability with overbias ratio is affected by the enabled ionization coefficients ratio and by the field dependences of ionization coefficients, which should be taken into account when choosing semiconductor materials for single photon avalanche diodes.