Determination of energy density distribution and capture cross-section of interface states in the metal-nitride-oxide-semiconductor (MNOS) structure

The capacitance and conductance of a metal-nitride-oxide-semiconductor (MNOS) capacitor was measured as a function of voltage at various frequencies between 10 Hz and 200 kHz using a “lock-in” amplifier. The capacitance as a function of voltage was also measured at a frequency of 1 MHz as well as under quasi-static conditions. All the measurements were made at a temperature of 298°K. The high-frequency C-V measurements were used to establish the relation between the surface potential and gate voltage. The experimental data was analysed in terms of the theoretical models of Lehovec and of Deuling et al. to determine the energy density distribution of the interface states. The interface states density calculated from the quasi-static capacitance measurements agreed with those obtained from the low frequency capacitance results analysed in terms of Lehovec's model. However, in the energy range between 0.5 and 0.9 eV, the vlaues of the interface states energy density calculated from fitting the conductance data to the model of Deuling et al. differ from those obtained by the other two methods by as much as a factor of two due to the high density of interface states in the MNOS device. The analysis of conductance data also furnished the values of electron capture cross-section which decreases approximately exponentially with interface states energy, varying from 10^?13 cm² at 0.4 eV to 10^?19 cm² at 0.86 eV.     

Optical subthreshold current method for extracting the interface states in MOS systems

Optical subthreshold current method (OSCM) is proposed for characterizing the interface states in MOS systems using the current-voltage characteristics under a photonic excitation. An optical source with a subbandgap (E/sub ph/相似文献   

Investigation of both interface states spectrum and deep oxide states from differential isothermal transient spectroscopy

Metal/insulator/Si (MIS) structures using a high-permittivity (high-k) dielectric layer, here the perovskite compound SrTiO₃, are investigated by differential isothermal transient spectroscopy in order to study electronic states at interface and inside the oxide. The isothermal transient capacitance responses of these MIS capacitors, obtained at varying depletion bias voltages and recording times, are analysed by fast Fourier transform (FFT). Different values of the accumulation pulse duration may induce changes in the trapped charge, allowing identification of the various mechanisms for restoring thermodynamical equilibrium in the interface states. Thus, discrimination between the proper contribution of interfaces states and that of oxide deep states is evidenced. The effects of several post-annealing of the oxide layer onto the energy spectra are also described.     

Transient thermo-reflectance measurements of the thermal conductivity and interface resistance of metallized natural and isotopically-pure silicon

The transient thermoreflectance method has been used to measure the thermal conductivity of natural silicon and isotopically-pure silicon-28 layers that are epitaxially grown on natural silicon substrates. The measurements were performed at room temperature for both a low level (10¹⁶) and a higher level (2×10¹⁹) of Boron doping of the epitaxial layers. The results indicate a gain of approximately 55% in the thermal conductivity of Si²⁸ as compared to that of natural Si, at both low and higher levels of doping, and a loss of approximately 19% for both types of silicon due to the higher level of doping.     

Extraction of interface state attributes from MOS conductance measurements

An algorithm is presented for the analysis of depletion MOS conductance-frequency measurements when fluctuations in band-bending are important. The interfacial trap density, standard deviation of the band-bending and the state time constants are found from pairs of measurements. The method is rapid and accurate to better than 1% over most of its range of application.     

Surface states at the nGaAsSiO2 interface from conductance and capacitance measurements

Conductance and capacitance measurements have been used to investigate the interface properties of MOS capacitors formed by depositing an insulating layer of SiO₂ on n-type GaAs. The surface potential as a function of applied bias is evaluated using results of high and low frequency capacitance measurements and the two methods are found to yield roughly similar results. The interface state density evaluated from the conductance and capacitance measurements is found to peak near the center of the band gap and also near the conduction band edge. Plots of conductance vs frequency indicate the presence of both fast and slow interface states in these materials.     

Interpretation for homojunctions of the difference between the theoretical and the experimental built-in potential determined from capacitance measurements, using interface states

The built-in voltage of a junction can be calculated theoretically and determined experimentally from capacitance measurements. The difference that is always found between these two values cannot be completely interpreted by taking into account the contribution to the capacitance of the free carriers. The remaining difference can be explained by assuming the existence of interface states in the vicinity of the junction. Formulas for the depletion-layer capacitance of abrupt and linearly graded junctions with interface states are derived. Experimental data are interpreted in relation to this model.     

Charge emission from interface states at silicon grain boundaries by thermal emission and thermionic-field emission—Part I: Theory

An extension of the theory for charge emission from monoenergetic grain boundary interface states by thermal emission (TE) and thermionic-field emission (TFE) is presented for states distributed in energy, whose density is either constant or slowly varying with energy as compared to the Fermi function. The importance of TFE increases with the doping concentrationN, and the voltage applied across the grain boundaryV, and decreases with increasing temperature. Interpretation of the interface state density according to the Seager-Pike-Ginley treatment, which neglects thermionic-field emission, is shown to overestimate the density and underestimate the interface state energies relative to the majority-carrier band.     

Charge emission from interface states at silicon grain boundaries by thermal emission and thermionic-field emission—Part II: Experiment

Comparison of the theory, developed in Part I of this paper [1], with transient capacitance experiments leads to the conclusion that the interface state energy distribution in grain boundaries is temperature dependent. This conclusion is based on experimental observations of the emission rate over a wide temperature range. One physical interpretation of this result is that contraction of the silicon material at reduced temperatures occurs primarily at the grain boundaries. A further result is that the doping concentration at grain boundaries in cast (Wacker Silso) silicon differs significantly from that in the bulk (inside the grains) of this material.     

Analysis of time domain radar cross-section measurements in compactranges

Radar cross-section measurements in the time domain are performed for the very first time, over a compact range. Apart from the hardware configuration and calibration used, extended analysis capabilities are discussed and illustrated with measurements. An enormous potential is envisaged in industrial and military applications, e.g. reverse engineering, radome optimisation and stealth design     

Optical frequency standards and measurements

We describe the performance characteristics and frequency measurements of two high-accuracy high-stability laser-cooled atomic frequency standards. One is a 657-nm (456-THz) reference using magneto-optically trapped Ca atoms, and the other is a 282-nm (1064-THz) reference based on a single Hg⁺ ion confined in an RF-Paul trap. A femtosecond mode-locked laser combined with a nonlinear microstructure fiber produces a broad and stable comb of optical modes that is used to measure the frequencies of the reference lasers locked to the atomic standards. The measurement system is referenced to the primary frequency standard NIST F-1, a Cs atomic fountain clock. Both optical standards demonstrate exceptional short-term instability (≈5×10^-15 at 1 s), as well as excellent reproducibility over time. In light of our expectations for the future of optical frequency standards, we consider the present performance of the femtosecond optical frequency comb, along with its limitations and future requirements     

Study of photocapacitance in diodes fabricated from silicon doped with vanadium

The levels of vanadium in the band gap of n-and p-Si were determined using photocapacitance measurements. It is shown that vanadium introduces levels only in the upper half of the band gap of n-Si; these levels have ionization energies of about E _c ?0.21 eV, E _c ?0.32 eV, and E _c ?0.52 eV. By contrast, V levels are located both in the upper and lower halves of the p-Si band gap: E _c ?0.26 eV, E _v +0.52 eV, E _v +0.42 eV, and E _v +0.31 eV. It is ascertained that the photoionization cross sections of all vanadium levels are larger for electrons than for holes. It is shown that the concentration of electrically active vanadium centers in n-and p-Si depends on both the concentration of shallow-level impurities and the time of vanadium diffusion into Si.     

Accurate determination of gain and radiation patterns by radar cross-section measurements

Using a two-port network and geometrical interpretation of equations involved in antenna scattering, it can be derived that antenna characteristics may be determined in properly designed scattering measurements. As an alternative to this approach it is shown that measurement procedures for gain and radiation pattern can be developed from simple considerations of the receiving, transmitting, and scattering properties of antennas. The main advantages of the technique are that no gain standard is required and a disturbing feedline to the antenna can be avoided. In addition to this the technique seems to be highly accurate. These general conclusions are well corroborated by experimental data on a standard gain horn. Sources of errors are outlined and compared with sources of errors in conventional techniques.     

介观RLC电路在热相干态和热压缩态下的量子涨落

利用热场动力学的方法研究了介观RLC电路在有限温度下的相干态和压缩态中电荷和磁通量的量子涨落.结果表明,介观RLC电路中电荷和磁通量的量子涨落不仅与电路中的元件参数而且可能与环境温度和压缩参数有关,而这些量子涨落与平移参数无关.     

Performance and testing of thermal interface materials

The increasing power and reduced die size of CPUs used in computers increases a need for significantly improved thermal interface materials (TIM). The TIM is used to reduce contact resistance at the CPU-heat sink interface. This work provides a state-of-the-art assessment on ‘thermal interface materials’, including fundamentals, materials used, their performance, and how interface resistance is measured. The performance of new commercial interface materials is given, as well as discussion of the advantages and disadvantages of different materials. The report notes that the recommended interface test method does not necessarily duplicate the installation and operating conditions in an actual computer installation. Recommendations are presented on the design and operation of an apparatus intended to simulate actual computer installation conditions. The innovative Penn State ‘low melting point alloy’ thermal interface material is described and compared to other commercial materials.     

Study of PtGaAs interface states

A capacitance study of a forward biased PtnGaAs junction has been used to determine the energy distribution and relaxation time of the interface states in equilibrium with the semiconductor. Experimental results show that interface states are distributed in two energy bands at given positions, densities and capture cross sections.     

Energetic distribution of interface states extracted from photo-conductance of organic thin film transistors

In this paper, a new method is introduced to obtain the energetic distribution of the interface states (density of states; DOS) extracted from the photo-conductance of organic thin film transistors (OTFTs) which exhibit varied transfer characteristics under illumination with different photon energies. The method was applied to pentacene OTFTs, and the results were compared with existing data. The major findings were not only the existence of the well-known peaks of DOS at 1.82 eV (free exciton of pentacene), and at 1.49 eV (extrinsic exciton due to dihydropentacene) but also new peaks were found at 1.25 eV, 1.29 eV, 1.31 eV, and 1.35 eV in the mid-gap. The new peaks were strongly enhanced under exposure to oxygen, and thus seem to be related to the defects associated with the presence of oxygen.     

Study of interface traps from transient photoconductive decay measurements in passivated HgCdTe

Generation-recombination (g-r) processes in the passivant/HgCdTe interface region are shown to complicate the transient photoconductive (PC) decays. Anomalous PC decays showing delayed peaks are observed and modeled for the first time. These peaks are correlated with the electron and hole traps in the interface region. Activation energy and density of the electron traps in the anodic oxide/n-Hg_0.78Cd_0.22Te interface region are estimated to be 12 meV and 1.1×10¹⁰ cm⁻², respectively. Density of hole traps is estimated to be 2.4×10¹⁰ cm⁻².