Showing papers on "Capacitance published in 1974"

Deep‐level transient spectroscopy: A new method to characterize traps in semiconductors

Abstract: A new technique, deep‐level transient spectroscopy (DLTS), is introduced. This is a high‐frequency capacitance transient thermal scanning method useful for observing a wide variety of traps in semiconductors. The technique is capable of displaying the spectrum of traps in a crystal as positive and negative peaks on a flat baseline as a function of temperature. It is sensitive, rapid, and easy to analyze. The sign of the peak indicates whether the trap is near the conduction or valence band, the height of the peak is proportional to the trap concentration, and the position, in temperature, of the peak is uniquely determined by the thermal emission properties of the trap. In addition, one can measure the activation energy, concentration profile, and electron‐ and hole‐capture cross sections for each trap. The technique is presented with a simple theoretical analysis for the case of exponential capacitance transients. Various traps in GaAs are used as examples to illustrate certain features of the DLTS technique. Finally, a critical comparison is made with other recent capacitance techniques.

Fast capacitance transient appartus: Application to ZnO and O centers in GaP p-n junctions

Abstract: New techniques and apparatus are presented which overcome some of the limitations of previous capacitance transient techniques and extend the useful range of capacitance transient measurements to intermediate depth impurity and defect states in semiconductors. This development greatly enhances the usefulness of capacitance techniques as a tool to study nonradiative recombination. These techniques and apparatus are used here to measure the electron‐capture cross sections and concentrations of isolated oxygen donors and ZnO complex luminescence centers in p‐type Zn‐ and O‐doped GaP. These results agree with the donor‐acceptor pairing theory and with the conclusion of previous capacitance measurements that the ioslated O donor is of negligible importance as a recombination center in these samples. Data is also presented which shows the effect of the junction electric field in greatly enhancing the thermal emission rate of electrons trapped in ZnO centers.

Signal, Noise and Resolution in Position-Sensitive Detectors

Abstract: An analysis is presented of signal, noise and position resolution relations for some of the most interesting position-sensing methods. "Electronic cooling" of delay line terminations is introduced in order to reduce noise in the position-sensing with delay lines. A new method for terminating transmission lines and for "noiseless" damping which employs a capacitance in feedback is presented. It is shown that the position resolution for the charge division method with resistive electrodes is determined only by the electrode capacitance and not by the electrode resistance, if optimum filtering is used.

Transient considerations of flat-plate solar collectors

Abstract: A mathematical study showed that a quasi-steady-state model which assumes zero capacitance adequately represents the performance of a flat-plate solar collector if hourly meteorological data are the best available. The use of more complex models which account for capacitance is justified only if better data can be obtained.

Properties of Au, Pt, Pd and Rh levels in silicon measured with a constant capacitance technique

Abstract: Measurements of emission rates and majority carrier capture cross-sections of Au, Pt, Pd and Rh centres in silicon are reported, and the activation energies associated with the different levels of these centres are determined. Where appropriate, our results are compared with values reported in the literature; other results have not been previously reported. The measurement depends on the emission and capture of majority carriers on the centres in the depletion layer of a p-n junction or Schottky barrier. The change in charge state of the centres is monitored by measuring the change in reverse bias applied to the junction necessary to keep the junction capacitance constant. The advantage of this technique, compared with the usual method of keeping the bias voltage constant and measuring the change in capacitance, is demonstrated.

Saturation capacitance of thin oxide MOS structures and the effective surface density of states of silicon

Abstract: The capacitance vs voltage curve of thin oxide (30–40 A) MOS structures in strong accumulation was studied. The results were interpreted in terms of equivalent surface density of state masses, which was found to be 0·2 m 0 for the silicon valence band and 0·06 m 0 for the conduction band, for both 111 and 100 surfaces. The experimental density of state masses were shown to be much lower than the bulk values. Equivalent density of states masses were calculated from a surface quantization model and in this case agreement with the experiments was obtained for the valence band only.

Interface and doping profile characteristics with molecular‐beam epitaxy of GaAs: GaAs voltage varactor

Abstract: Studies of the doping profile characteristics of molecular‐beam epitaxy (MBE) of GaAs on GaAs substrates are reported. Highly resistive regions at the substrate—epitaxial‐layer interface, and within the epitaxial layer, may occur if the growth is interrupted. It is shown that almost any arbitrary voltage dependence of the capacitance of such structures can be achieved by varying the dopant deposition rate during epitaxy. To illustrate the versatility of this growth technique, voltage‐variable capacitors have been prepared with Schottky barriers on MBE GaAs layers with precisely controlled doping profiles. Low‐frequency measurements (up to 100 MHz) demonstrate that capacitance variations in excess of a factor of 10 have been achieved by varying the applied bias voltage V from 0.3 V (with no significant forward conduction) to −1.0 V. The feasibility of frequency tuning diodes with C−1/2[sine wave]φ−V, where φ is the effective barrier height, is shown. At ‐3 V bias, cutoff frequencies >40 GHz have been measu...

Large value capacitor

Abstract: Disclosed is a semiconductor capacitor which utilizes the volume of the semiconductor substrate in which it is formed to create increased surface area and thereby to provide increased capacitance. The surface area is increased by forming selectively spaced grooves in the surface of the semiconductor substrate by orientation dependent etches and utilizing the sidewalls of the grooves as surface. Groove depth is limited to a predetermined value by etching time, geometrical constraints, or by etch stops. This provides for precise control of capacitance values on a batch or commercial basis. Increases up to at least 100-fold in capacitance as compared to a flat capacitor structure as possible. A thin layer of dielectric is formed over the increased surface area, and thereafter a conducting layer is formed over the dielectric layer to provide a dielectric capacitor. An active junction P-N capacitor may also be formed.

Characterization of the interface states at a Ag/Si interface from capacitance measurements

Abstract: From the variation of the quasi‐Fermi levels at the interface of a Ag–Si diode under forward bias, we present a new way to characterize the interface states of such an interface from capacitance and conductance measurement. We obtained the density, the time constant, and the capture cross section of the interface states. The relative energy distribution of the interface states is in close agreement with those deduced from our photoelectric measurements. Such a determination implies that interface states are in equilibrium with silicon, in agreement with Heine's theory.

Mechanism and properties of point‐contact metal‐insulator‐metal diode detectors at 10.6 μ

Abstract: Detection mechanisms of point‐contact MIM diodes at 106 μ wavelength have been studied Detailed measurements of the static current‐voltage characteristic and its first and second derivatives as functions of bias voltage were made simultaneously with infrared sensitivity measurements The results indicate that the static current‐voltage characteristics extend to infrared frequencies We find that thermal effects do not contribute significantly to detection at this wavelength, and that the tungsten whisker acts as a rather efficient receiving antenna The antenna and its shunting capacitance apply a 3×1013‐Hz ac voltage to the diode which in our experiment has amplitude 124 mV, through an impedance which is much less than the junction impedance The diode nonlinearity d2I/dV2 varies from 65×10−5 to 67×10−3 A/V2 as dc bias increases from 0 to 300 mV None of these conclusions apply to detection at 6328 A; it is found that detection in the visible is dominated by thermal or photoconductive effects

Field-enhanced carrier generation in MOS capacitors

Abstract: When sufficiently high voltage steps are used for driving a metal-oxide-semiconductor capacitor (MOSC) towards deep inversion, the temporal evolution of the current and of the high-frequency capacitance during the return to equilibrium cannot be interpreted on the basis of a theory assuming a constant bulk generation lifetime. A more general theory, which takes into account field-dependent carrier emission rates, is developed and it is shown how current and h.f. capacitance measurements can be used to determine the field dependence of the bulk generation lifetime. The results of experiments performed on differently processed MOSC's are presented; they support the hypothesis that field-enhancement of carrier emission rates takes place according to a mechanism of the Poole-Frenkel-type.

New NBS Measurements of the Absolute Farad and Ohm

Abstract: A recently completed calculable cross capacitor in conjunction with a previously described collection of ac and dc bridges has made possible a highly accurate measurement of the farad and the ohm. The cross capacitor and its auxiliary equipment, as well as those components of the measurement system which have not been covered in prior publications, are described in detail. The measurements indicate that the National Bureau of Standards (NBS) unit of capacitance is given by FNBS = 1 F + 1.787 ?F, and that the NBS unit of resistance is given by ?NBS = 1 ? - 0.819 ??.

Interfacial photoreactions and chemical capacitance in lipid bilayers.

Abstract: The electrical response of a pigmented lipid bilayer to a short laser pulse is measured by a tunable voltage clamp method. In this method, a variable access impedance permits “tuning” of the observed relaxations for optimal measurements. Analysis of the data so obtained leads to an equivalent circuit that contains a novel chemical capacitance charged by the specific photoreaction across a single membrane-water interface. This chemical capacitance is distinct from the ordinary membrane capacitance. The intrinsic chemical rate constant obtained from the equivalent circuit analysis is shown to be the pseudo-first-order rate constant of the reverse dark reaction of the reduced acceptor and the oxidized pigment. The tunable voltage clamp method of measurement and analysis allows unambiguous separation of this rate constant into resistive and capacitative elements, which are interpreted in molecular terms.

Pushbutton capacitive transducer

Abstract: An electro-mechanical transducer for use in keyboards and the like which incorporates a capacitance change utilization concept. The transducer includes a plunger assembly reciprocably disposed in a housing therefor, in operative disposition over capacitance forming areas on an insulated substrate. The plunger assembly includes a key button disposed on one end of a shaft, an intermediate flange on the shaft and a flange at the other end of the shaft. The intermediate flange is positioned adjacent a frusto-conical elastomeric return spring and also serves as a resilient stop for the shaft. A compressible foam or sponge-like material having a thin, flexible metalized dielectric material on its lower portion, is mounted on the lower surface of the other flange. Actuation of the shaft downwardly toward the substrate causes the dielectric material to bridge the capacitance forming areas related thereto to cause a change in capacitance and transfer of energy therebetween. The metalized dielectric material is highly flexible to allow it to readily conform to irregularities in the capacitance forming area.

Surface-state spectra from thick-oxide MOS tunnel junctions

Abstract: The conductance and capacitance of thick-oxide MOS tunnel junctions (SiO2 thickness 40 to 65 A) have been measured from 35 Hz to 210 kHz. It is demonstrated that the use of a thick-oxide MOS tunnel junction makes it possible to obtain the surface-state data throughout the whole silicon band gap with better resolution and better sensitivity than the conventional MOS capacitance techniques. A slight departure from equilibrium may occur in the voltage range where large tunnel current flows. Corrections to the energy scale must be made in this voltage range. A method for the evaluation of the junction quality is discussed. The simplified equivalent circuits necessary for the calculation of surface-state data are constructed under various bias conditions by an approach different from that used in a previously published work. The present work supports the model that at least some of the observed surface states are a consequence of the diffusion of contact metals into the oxide.

A servo controlled Fabry-Perot interferometer using capacitance micrometers for error detection

Abstract: A servo controlled Fabry-Perot interferometer using capacitance micrometers to sense departures from parallelism and variations in the mean spacing of the Fabry-Perot plates is described. The parallelism and mean spacing of the plates is maintained over the full 75 mm aperture of the instrument to an accuracy better than the surface quality of the plates ( approximately lambda /150 at 500 nm).

Deep levels in gallium arsenide by capacitance methods

Abstract: The three capacitance methods, i.e., TSCAP, PHCAP, and transient capacitance measurements, are applied to determine electronic properties of deep levels inn-GaAs. In the boat-grown wafer detected are the 0.30 eV electron trap withNT=3.6×1016 cm−3 andSn=2.4×10−15 cm2, and the 0.75 eV electron trap withNT=2.0×1016 cm−3 andSn=1.2×10−14 cm2. In the epitaxial wafer, the 0.45 eV hole trap is detected withNT>1.5×1013 cm−3 andSp=1.4×10−14 cm2 as well as the 0.75 eV electron trap withNT=2.4×1013 cm−3.

Magnetostriction Measurement by Three Terminal Capacitance Method

Abstract: The saturation magnetostriction constants λ100 and λ111 of YIG and Fe(1-x)Alx (x=0.17, 0.20, 0.23, 0.25) single crystals were measured by a capacitance method at room temperature. The capacitance cell used in this experiment was designed to be convenient for measuring the constants of spherical samples from 0.5 mm to 10 mm in diameter with sufficient sensitivity to measure elongations of 0.1A. The magnetostriction constants λ100 and λ111 of YIG were -1.43×10-6 and -2.88×10-6 respectively and were in very good agreement with the values observed by Callen, Clark, DeSavage, Coleman and Callen.

Characterization of multiple deep level systems in semiconductor junctions by admittance measurements

Abstract: The small signal admittance, Y, of a junction device, in the presence of deep lying majority carrier traps, is obtained as a solution to a simple differential equation (dC/dχ) = (C2/e)−(ρac/ψac), where C Y/jω is the complex capacitance, x is the distance within the depletion region from the neutral bulk semiconductor, ρac is the a.c. incremental change in charge density at χ when the bias is incremented by ψac. This equation can be numerically integrated with one boundary condition, the flat band capacitance of the bulk semiconductor. An analytic solution to the above differential equation is possible over a wide frequency range without the use of a truncated space charge approximation. The admittance of one half of a junction device can then be modelled by a 3p + 1 lumped element equivalent circuit involving 3p + 2 device parameters, where p is the number of species of deep lying majority carrier traps that are virtually unionized in the bulk. These circuit elements bear simple direct relationships to the deep level parameters. Impedance vs frequency measurements at a single bias and temperature yield only 2p + 1 equations and are not sufficient to define the elements uniquely. One therefore needs p + 1 additional equations for a unique synthesis. We also show how additional equations can be obtained from impedance vs voltage or temperature measurements.

A detailed analysis of the metal-semiconductor contact

Abstract: A general quantum and electronic theory able to explain the electric and photoelectric experimental properties of the metal-semiconductor contacts is proposed. The theory consists firstly in calculating the electric space charge due to the quantum mechanical tunneling of the electrons from the metal into the semiconductor, and vice-versa, and to the metal and semiconductor bands bending. Then the electric charge so obtained is utilised to solve in an appropriate and complete way the Poisson equation so as to determine the electric field and potential as functions of the abscissa x. The electric field F(x) is employed to obtain a new expression for the junction capacitance C, holding in the general case of a non-uniform charge, whereas the electric potential νi(x) is used to calculate general expressions for the thermionic and photoelectric currents i and iph, respectively, taking into account in this both the tunneling probability through the energy barrier and the many-valley structure of the semiconductor energy bands. Finally, from νi(x), C, i and iph four new expressions of the energy barrier height of the contact are deduced. The theoretical results relative to the barrier height so determined (which hold for both n-and p-type semiconductors) are compared with published experimental values obtained, by means of capacitance and photocurrent measurements: (a) on contacts between n-type CdS and Au, Cu, Ag and Pt; (b) on contacts between n-type GaAs and Au, Ag, Cu, Sn, Al and Pt and; (c) on contacts between p-type GaAs and Au and Al. The agreement between the theoretical and experimental values is very good.

Noise measurements on the floating diffusion input for charge‐coupled devices

Abstract: A technique is presented for electrically introducing charge into a charge‐coupled device (CCD) in a stable uniform low‐noise manner. The technique utilizes a floating diffusion whose capacitance (Cfd) can be tailored for particular applications or monitored directly for noise measurements. Experimental results are presented which demonstrate that charge can be introduced into a CCD with a variance of kTCfd. This technique is particularly germaine to the introduction of a ``fat zero'' into a low‐light‐level surface channel CCD imager.

Frequency selective damping circuits

Abstract: In A.C. power systems, large capacitors used in conjunction with synchronous or induction machines, or with saturable reactors, are prone to self-excited oscillation at harmonic or sub-harmonic frequencies. Damping circuits are known in which supply-frequency capacitor current is kept away from a damping resistance path by a series or shunt resonant circuit. The invention provides improved damping of harmonic or sub-harmonic oscillations by adding capacitance or inductance, or both, to achieve a resonance at the parasitic frequency and so force the parasitic current through the damping resistance.

Charge transfer device decoder and compander

Abstract: A charge transfer device is disclosed for performing decoding and companding functions in analog-to-digital conversion. In one embodiment, varying amplitude pulses from a pulse amplitude modulator produce charge carriers in the semiconductor medium which are introduced beneath a first row of charge transfer electrodes. As each potential well beneath an electrode is filled, the charge carriers spill into the adjacent well down the row such that the number of charge packets collected is proportional to the amplitude of the input pulse. Compression of the signal is accomplished by varying the capacitance along the row. The charge packets may be read out serially from this row or transferred laterally to a second row of electrodes and read out from this row in serial fashion. In a further embodiment, equal amplitude pulses produce charge carriers introduced beneath a first row of electrodes which controls the passage of charge from a source of carriers to another row of electrodes. The latter row of electrodes has an increasing capacitance to expand the input signal. The carriers present under the second row are accumulated at the end of the row to produce a signal which is proportional to the number of pulses at the input.

Fluid density measuring system

Abstract: This invention relates to a fluid density measuring device comprising spaced capacitor electrodes between which fluid under measurement can flow. The capacitance between the plates is a function of the density of the fluid. An oscillator drives an alternating current between the capacitor electrodes, the magnitude of the current being proportional to the capacitance between the electrodes. A reference current of a magnitude equal to a predetermined value corresponding to an expected minimum fluid density is subtracted from the actual current between the electrodes to produce a signal directly proportional to the variation of fluid density. This signal is then amplified, and thereafter a bias signal accurately representing a minimum fluid density is then added back to the amplified density variation signal to produce an output signal directly proportional to the fluid density. This signal can be fed to any suitable display or control equipment.

Touch actuated electronic switch

Abstract: An electronic switch which has no moving parts and is actuated by the capacitance of an operator providing a connection between earth ground and an input to the electronics associated with the switch is disclosed. The electronic switch in the preferred embodiment, includes a plate accessible to the tough of a human operator electrically connected to a first amplifier, and particularly to the input which is isolated from and thus oscillating with respect to earth ground. The output of the first amplifier is simultaneously connected to one end of a storage capacitor, having its other end connected to earth ground, and to one end of a high impedance. A second amplifier, is connected to the other end of the high impedance to provide a switched output, with the switched output having a first state for approximating an electrical short circuit and a second state for approximating an electrical open circuit.