A compact microcomputer-based deep level transient spectroscopymeasurement system

A specifically designed system for deep-level transient spectroscopy (DLTS) measurement is described. It is compact and fully automated, can measure all the spectra in just one temperature scan, and permits simultaneous analysis of two devices. The user sets up the measurement conditions with a reduced number of commands. This makes the system very flexible and versatile. A self-scaled gain output amplifier has been incorporated to provide the maximum DLTS signal amplitude compatible with the input range of the analog-to-digital (A/D) converter. This self-scaling allows the detection of traps with a large amplitude range. Up to 90 sampling times can be selected for each transient. To improve the signal-to-noise ratio (SNR), as many as 32768 scans may be accumulated for averaging. Improvements as high as 45 dB have been used to characterize deep centers in AlGaAs/GaAs devices grown by liquid-phase and molecular-beam epitaxies     

Characterization of deep levels in high electron mobility transistor by conductance deep level transient spectroscopy

The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) on silicon (111) substrate is profited to investigate traps that are located between the substrate and the two-dimensional electron gas (2DEG) channel. The transient of the drain current after applying a negative substrate voltage is evaluated in the temperature range from 77 to 600 K. With this method, known as Conductance Deep Level Transient Spectroscopy (CDLTS), majority deep levels with activation energy of 61 meV as well as minority carrier traps at 74 meV and capture cross-section respectively 2.56 × 10^− 15 cm², 2.1 × 10^− 15 cm² are identified. Finally, the correlation between the anomalies observed on the output characteristics and defects is discussed.     

A computer controlled,high performance,neutron coincidence counting system

A circuit to implement the neutron coincidence algorithm of Böhnel is described. The circuit uses static memory devices to store the pulse trains and has a throughput of 4M pps. It has a wide range of computer controlled operating parameters. It is suitable for monitoring plutonium in bulk or in small quantities contained in crates or drums of waste. The circuit has been in use for several years and has been found to be reliable. Full circuit diagrams are included.     

Measuring the capacitance of individual semiconductor nanowires for carrier mobility assessment

Capacitance-voltage characteristics of individual germanium nanowire field effect transistors were directly measured and used to assess carrier mobility in nanowires for the first time, thereby removing uncertainties in calculated mobility due to device geometries, surface and interface states, and gate dielectric constants and thicknesses. Direct experimental evidence showed that surround-gated nanowire transistors exhibit higher capacitance and better electrostatic gate control than top-gated devices, and are the most promising structure for future high performance nanoelectronics.     

一种精密电容测试系统设计

该文介绍一种基于自动平衡电桥的精密电容测试系统设计方法,通过对激励信号与自动平衡电桥输出信号进行鉴相分析,给出被测电容值的计算方法。为使鉴相器处于最佳工作点,得到精度更高的电容值测量结果,系统对自动平衡电桥输出信号进行反馈,并根据反馈结果,结合标准电阻选择与程控放大器对信号进行调理。最后,在1 MHz的测试频率下对系统的电容测试精度进行验证,得出设计的电容测试系统具有较高的测试精度。     

Characterization of deep level defects in Si irradiated with MeV Ar+ ions using constant capacitance time analyzed transient spectroscopy

An isothermal spectroscopic technique called time analyzed transient spectroscopy (TATS) in the constant capacitance (CC) mode has been used to characterize electrically active defects in the MeV Ar⁺ implanted silicon. The problems associated with high defect density and the presence of damaged region in the as-implanted material are overcome by CC-TATS method. The CC-TATS spectra of the as-implanted sample shows two positive peaks and an attendant negative peak. Two distinct traps have also been identified using thermally stimulated capacitance method modified to operate in constant capacitance mode. Variable pulse width measurements using CC-TATS show exponential capture kinetics in contrast to extremely slow capture observed in conventional deep level transient spectroscopy (DLTS) experiment. The results indicate that trapping behaviour is due to point-like defects associated with extended defects such as dislocation and stacking fault.     

Deep levels in GaN studied by deep level transient spectroscopy and Laplace transform deep-level spectroscopy

In this study we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77–350 K. Si-doped GaN layers were grown by Molecular Beam Epitaxy technique (MBE) on sapphire substrates. DLTS signal spectra revealed the presence of four majority traps: two hightemperature and two low-temperature peaks. Using LDLTS method and Arrhenius plots the activation energy and capture cross sections were obtained. For two high-temperature majority traps they are equal to E1 = 0.65 eV, σ₁ = 8.2 × 10^?16cm² and E2 = 0.58 eV, σ₂ = 2.6 × 10^?15 cm² whereas for the two low-temperature majority traps E3 = 0.18 eV, σ₃ = 9.72 × 10^?18 cm² and E4 = 0.13 eV, σ₄ = 9.17 × 10^?18 cm². It was also found that the traps are related to point defects. Possible origin of the traps was discussed and the results were compared with the data found elsewhere [1–5].     

Reliable timing systems for computer controlled accelerators

Over the past decade the use of computers has set new standards for control systems of accelerators with ever increasing complexity coupled with stringent reliability criteria. In fact, with very slow cycling machines or storage rings any erratic operation or timing pulse will cause the loss of precious particles and waste hours of time and effort of preparation. Thus, for the CERN linac and LEAR (Low Energy Antiproton Ring) timing system reliability becomes a crucial factor in the sense that all components must operate practically without fault for very long periods compared to the effective machine cycle. This has been achieved by careful selection of components and design well below thermal and electrical limits, using error detection and correction where possible, as well as developing “safe” decoding techniques for serial data trains. Further, consistent structuring had to be applied in order to obtain simple and flexible modular configurations with very few components on critical paths and to minimize the exchange of information to synchronize accelerators. In addition, this structuring allows the development of efficient strategies for on-line and off-line fault diagnostics. As a result, the timing system for Linac 2 has, so far, been operating without fault for three years, the one for LEAR more than one year since its final debugging.     

A simple computer method for predicting the transient response of ultrasonic NDT probes

This paper describes a computer method for predicting the transient response of compressional wave ultrasonic probes employing piezoelectric disc transducers. Simple programs provide detailed predictions for both the form of the ultrasonic pulse transmitted to a test material and also the voltage output corresponding to the reception of the said ultrasonic pulse. The effects of intermediate layers lying between transducers and backings and between transducers and test materials are included. The electrical input to a transmitting prode is assumed to be a single, unipolar current pulse, whilst a receiving probe is assumed to work into an electrical open circuit.Excellent agreement between theoretically predicted and experimentally observed waveforms has been obtained for specially constructed immersion probes.     

A computer system for analysis of chromatographic data

Marshall, R.J., Bleasby, A.J., Turner, R. and Cooper, E.H., 1987. A computer system for analysis of chromatographic data. Chemometrics and Intelligent Laboratory Systems, 1: 285–295.An interactive computer program (CHAS) for chromatogram processing is described. CHAS is a FORTRAN program which has three basic functions: (a) for data management, (b) for graphical display, and (c) for chromatogram analysis. The program is designed to run off-line by accessing data from a library of chromatograms. Various types of graphical displays are available and its analytical procedures incorporate new algorithms to detect chromatogram peaks, to remove baseline drift and to compute similarities between chromatograms. We present some illustrative uses of the program for data generated by high-pressure liquid chromatography.     

A novel direct reading active-RC system for measurementsof in-circuit, discrete, and incremental capacitances

A simple, low-component active-RC circuit is given for the measurement of in-circuit, discrete, and incremental capacitances. The measurement circuit provides the measured value of capacitance directly in terms of the circuit's output voltage. The proposed system provides good accuracy for these measurements. The capacitance measurements are independent of the signal frequency. Experimental results that support the theory are included     

Study of deep levels in Schottky/CuInSe2 single-crystal devices by deep-level transient spectroscopy measurements

Deep-level transient spectroscopy (DLTS) measurements performed on Schottky/CuInSe₂ diodes are reported. So far, Cd(Zn)S has been used as a window n-type layer to prepare CuInSe₂ diodes. The diffusion of such a layer introduced defects into Cd(Zn)S-CuInSe₂ diodes. Thus, the importance of using Schottky diodes lies in the elimination of the window n-type layer diffusion into CuInSe₂ material to reveal the intrinsic properties of the semiconductor. A comparison between previously reported defect states in Cd(Zn)S-CuInSe₂ and those found in Schottky/CuInSe₂ is made.The defect concentration is calculated as well as the capture cross-section. Some of the defect levels agree with previously published data. A common feature exhibited in all the measured samples is that the capacitance transient is non-exponential, and the DLTS spectrum is relatively broad, due to the contribution of two or more closely spaced levels.     

Spectroscopic methods for noise levels in semiconductor materials and devices

Conclusions Theoretical relationships have been derived that associate the characteristics of modulated GR-noise with the parameters of the various kinds of levels located in an SCR. These relationships can be utilized to calculate the modulated GR-noise in a broad class of devices and structures. It has been shown that an essential role may be played in the formation of this noise by the fluctuations that accompany the adherence of current carriers in a narrow region of a SCR. It is revealed that during the flow of large collector currents in transistors or of large photocurrents in photodiodes the role of adherence noise from minority carriers, as well as of recombination noise, is increased. Two different kinds of methods for barrier-noise spectroscopy of the levels are proposed.The materials in the article were presented at the 6th All-Academic School for Standardization and Metrological Problems.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 59–61, March, 1990.     

A computer aided design system for artistic Chinese fonts

Abstract

The design of artistic fonts for characters is used for producing special visual effects via the shape and color changes on the character fonts. The various changes on the shapes of fonts can be achieved by changing the boundary curves of fonts which are represented by spline functions. In this paper, we focus our attention on the Chinese character fonts. A mathematical simulation of simplifying two dimensional and three dimensional surface projection is provided. The implementation of the system is presented with illustrative examples.     

Neutron-irradiation-induced defects in germanium: A Laplace deep level transient spectroscopy study

Deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and L-DLTS combined with uniaxial stress have been used in this work for characterization and identification of electrically active defects induced in Sb-doped germanium crystals by irradiation with fast neutrons. The samples were irradiated with relatively small doses of neutrons (≤5 × 10¹¹ cm⁻²) in order to produce uniformly distributed damage and to detect small defect clusters. It is found that for such low neutron doses in many respects the damage produced is similar to that resulting from electron irradiation. Vacancy-antimony (V-Sb) pairs uniformly distributed in the sample bulk are the dominant defects observed in the DLTS spectra. It is inferred from the L-DLTS measurements under application of uniaxial stress that the V-Sb pair has a trigonal symmetry in the doubly negatively charged state. It is argued that an electron trap with the activation energy for electron emission of 0.1 eV is related to an acceptor state of a small vacancy cluster located in highly damaged regions of the neutron-irradiated samples. L-DLTS measurements under application of uniaxial stress indicate that the symmetry of the defect is low, monoclinic-I, C_1h point group, or lower. Environment-induced broadening of the L-DLTS signal due to this centre prevents precise determination of the defect symmetry.     

FATSYS,a computer controlled system for fatigue crack growth data collection using an Amsler Vibrophore

A system of hardware and software developed for collecting fatigue crack growth data from an Amsler Vibrophore fatigue machine is described. The system allows testing at constant, increasing and decreasing stress intensity factor ranges ($\text{ΔK}$), and it generally complies with the proposed ASTM standards on fatigue crack growth testing. The system has proven to be extremely beneficial particularly for work at growth rates approaching threshold, where manual methods are tedious and time consuming.