Showing papers in "International Journal of Electronics in 1968"

Potential distribution and capacitance of abrupt heterojunctions

Abstract: The transition region analysis of an abrupt heterojunction is extended to include the effects of mobile carriers‘ charge in the space charge regions. Deviations from the depletion model are obtained when the wide band-gap semiconductor is heavier-doped-This is due to a non-negligible potential drop across the narrow band-gap semiconductor at an isotype (i.e. n-n or p-p) heterojunction, and to an inversion layer at the interface in the same semiconductor at an anisotype (i.e. p-n or n-p) heterojunction. The C−2 versus V plots are acceptable, straight lines having slopes in agreement with the depletion model predictions, but the intercept voltages differ. A constant electric dipole at the interface causes a similar effect.

The electrical characteristics of nZnSe—pGe heterodiodes†

Abstract: The forward and reverse current-voltage characteristics and reverse-biased capacitance are described for the nZnSo-p+ Ge emitter-base diodes of heterojunction transistors The forward diode current flow involves essentially electron injection into the Go together with loss-mechanisms of recombination of injected electrons through interface states and, probably, electron capture into ZnSo traps followed by tunnelling into interface states In the junctions that have been fabricated, the current-voltage characteristics are dominated by the high resistivity bulk ZnSo in series with the junction, resulting in space-charge-limited flow The reverse junction characteristics demonstrate semi-saturation, avalanche multiplication, and negative resistance The junction capacitance is strongly frequency dependent duo to the presence of relatively deep traps, and both abrupt and linearly graded junctions have boon observed, depending on the growth technique

The epitaxial growth of silicon in horizontal reactors

Abstract: A theory is proposed for the epitaxial growth of silicon in horizontal reactors operating under conditions which result in a large proportion of the chlorosilane being converted into silicon. The transport equation is solved for the case where the equilibrium reactions are: by assuming that the gas velocity profile is a constant over a plane perpendicular to the direction of gas flow, and that the temperature is everywhere constant in the reaetor. The resulting expression for the growth rate is compared with the experimental values with trichlorosilane as the source of silicon, and it is shown that reasonable agreement obtains. Associated Semiconductor Manufacturers Ltd. is a joint Mullard/G.E.C. company responsible for the development and manufacture of Milliard semiconductor devices.

Avalanche breakdown of gallium arsenide p-n junctions†

Abstract: The ionization coefficient of carriers in gallium arscnide has been measured over the field range (2.5-5) × 105 v cm-1. The ionization coefficient, which has been previously shown equal for holes and electrons, was found to exhibit a field dependence given by α=α∞ exp {—(b/8)2} where α∞= 2.0×105cm−1 and b=5.5× 105 v cm−1. This is in fairly good agreement with recently reported data, but indicates a higher ionization coefficient in the lower field range. Consequently, the predicted breakdown voltages are slightly lower than those previously calculated, but in better agreement with experimental values. The difficulty in fitting the ionization coefficient with present theory is believed to be duo to the details of the band structure which are neglected in present theories.

The effect of ambient, temperature and cooling rate, on the surface charge at the silicon/ silicon dioxide interface†

Abstract: The influence of ambient, temperature and cooling rate, in determining the surface charge at the silicon/ silicon dioxide interface has been experimentally investigated. The results, in conjunction with previous work, have enabled some of the characteristics of the surface charge to be established.

Surface waves on inhomogeneous plasma columns.

Abstract: Quasistatic theory is presented for axially symmetric and dipolar surface modes propagating down an inhomogeneous plasma column enclosed in a glass tube surrounded by free space. The effect of a sheath with no electrons present, radial parabolic electron density distribution, and the combination of these two effects on the dispersion relations of the axially symmetric and the dipolar modes is investigated for lossless, cold and isotropic plasma. Parabolic density variation is treated approximately by a variational technique. Dispersion relations for all three examples of inhomogenoity for both the n = 0 and n =1 modes are calculated for a wide variety of parameters of inhomogeneity. The dipolar mode is seen to be more sensitive to inhomogeneous electron density distribution than the axially symmetric mode for small βa and is thus better suited for experimental verifications than the axially symmetric mode.

Notes on constricted and unstable positive columns in electronegative gases

Abstract: A survey has been made of experiments on constricted and unstable positive columns in electronegative gases at relatively low pressure. A provisional division of columns is proposed into those where large negative ions or massive negatively charged particles are present, and those where only small molecular or atomic ions occur. Some new experimental results are described for iodine. Diffuse columns have properties like those of diffuse columns in electropositive gases, modified by the presence of negative ions. Filamentary highly-concentrated discharges appear to be arcs. Attention is called to Kracik's helical perturbation theory of instability. Seeliger and Sommermeycr's theory of unstable columns, in which the core and wall are supposed to be uncoupled by loss of electrons through attachment, is developed further. A method is proposed for assessing the contribution of massive particles to instability by supposing that they provide surfaces distributed through the volume of the discharge on which recom...

Noise generation under large signal conditions in the Read microwave avalanche diode

Abstract: In this report the noise generation mechanism of the Read microwave avalanche diode is examined. Using a large signal approximation to the operation of the device as an oscillator, the current variation with time in the avalanche region is examined and an expression for the variance of this current, due to fluctuations in the ionization process, is obtained. The effect of this, current variance upon the output waveform of the device is then investigated It is found that as the bias current is increased the output waveform rapidly becomes very noisy. This is due to the build-up mechanism of the avalanche which tends to amplify the ionization fluctuations occurring while the current is small. Various means of reducing this effect are considered, the most promising of which seems to involve widening the avalanche region of the device. Finaly, expressions are derived for the F.M. and A.M. noise characteristics which would be obtained at the output of a microwave oscillator driven by a Head diode. The expected...

Characteristics of the Darlington composite transistor

Abstract: The characteristics of the Darlington composite transistor are discussed on the basis of the hybrid parameters. The variation of the hybrid parameters of this configuration with operating conditions is also investigated in the common emitter and common base connections. The performance of the Darlington transistor amplifier is described and a set of curves are given showing the variation of its performance attributes with source and load resistances.

Temperature dependence of avalanche breakdown in gallium arsenide p—n junctions†

Abstract: The ionization coefficient of carriers in gallium arsenide has been measured over the temperature range − 20°c to +80°c. It has been found to obey the relationship α α∞exp { −(b/ )): } where both α∞and b are functions of temperature. The temperature coefficients of α∞ and b obtained from these measurements have boon used to predict the temperature coefficient of gallium arsenide p-n junctions, and these values have been found to be in good agreement with reported observations.

Stability and surface charge in the MOS system

Abstract: Results are presented which show that the surface charge and the stability of the MOS system are not directly related. The centres responsible for the surface charge are located close to the silicon surface and their density is independent of the silicon resistivity, the slice pre-oxidation treatment, the silicon surface potential over a wide range of the silicon energy gap and the oxide growth rate. The surface charge is, however, a function of the oxide thickness and the time and temperature of post oxidation annealing in nitrogen. Associated Semiconductor Manufacturers Limited is a joint Mullard/ G.E.C. company responsible for the development and manufacture of Mullard semiconductor devices.

Drift-field photovoltaic cell performance with bulk and surface recombinations†

Abstract: An analytical study of the losses at the surface and in the bulk of a drift-field photovoltaic cell has boon made and their influence on the performance of the device has been evaluated. The study has been made with particular reference to the drift field in the base region, surface recombination velocity and base width.

Ionization coefficients and sparking voltages in argon-methane and argon-propane mixtures†

Abstract: Townsend primary and secondary ionization coefficients have been measured in 0.03, 0.3 and 3% of methane and of propane in argon for a total pressure in the range 0.5-500 torr and for a uniform field gap up to 1 cm. The primary ionization coefficient for the Ar-CH4 mixtures remains within 30% of that for pure argon but an optimum concentration of 0.13% of propane in the Ar-C3H8 mixture gives rise to a Penning effect almost comparable in intensity to that observed by Kruithof and Penning (1937) in Ne-Ar mixtures; thus at E/p0 =5 v cm−1 torr−1 at 0°c, the coefficient is increased by a factor of 200 above that for pure argon. Because of the quenching property of hydrocarbons, it is shown that it is possible to reduce the secondary ionization coefficient of argon as much as 107 times; at low and high E/p0 the effectiveness of quenching incroasos with increase of molecular weight whilst in the intermediate rogion 10≲ E/p 0 ≲100, the reverse is the case. At an optimum concentration of 0.03% of propane ...

Total inelastic cross sections for slow electrons in xenon

Abstract: An electron beam of low energy enters a cubic wire gauze chamber in Xe at a pressure of about 10−2 torr. The scattered electrons escaping from the chamber are received by a collector kept at a retarding potential of frac13; of the accelerating voltage. When inelastic collisions duo to excitation sot in, the collector current decreases. In order to derive from this change the absolute cross section, the average number of electron collisions in the chamber must be known; this was determined in two ways. With this result and the observed variation of the collector current with the accelerating voltage the total excitation cross section is found between the lowest excitation potential of 8-2 v and the ionization potential of 12-1 v; multiple scattering, energy spread and closeness of energy levels of Xe prevent the appearance of a fine structure. For energies up to 15 v approximate cross-section values are obtained after allowing for the positive ion current and including the known ionization cross sections. ...

Space-charge waves and high-frequency negative resistance of SCL diodes†

Abstract: In this paper the small-signal operation of space-charge-limited (SCL) diodes is studied in detail, by using a quantitative method previously suggested by the author. Typical cases, such ns SCL dielectric diodes with traps or field-dependent mobility, the punched-through SCL diode, the bulk negative mobility amplifier with zero ion density, the SCL vacuum diode, are included. The transport of space charge and the inertia of the carrier velocity with respect to electric field variations are both taken into account, in order to explain high-frequency negative resistance effects. ‡Permanent address: Department of Electronics, Polytechnieal Institute, Bucharest, 62, Romania.

A broad-band parametric amplifier†

Abstract: This paper describes a broad-band parametric amplifier potentially suitable, for example, as the front amplifier in the ground station receiver of advanced satellite communication systems. A single stage with l0db gain at 4 GHZ has given 20% bandwidth to 033 dB points. The amplifier is capable of cryogenic operation for low noise performance and several stages have been cascaded for higher gain. A novel feature of this amplifier is that it employs an idler circuit with a double peaked response. This approach has led to the development of very simple broad-banding controls which can be adjusted under actual operating conditions even when the amplifiers are refrigerated.

An introduction to the generalized field theory I. Forward conduction in p— n junctions and heterojunctions†

Abstract: Recently it has been suggested that thermal equilibrium and non-equilibrium, in some systems containing interfaces, could be accounted for by a new phenomenologieal theory, which lends itself to new statistical mechanical interpretations, and which has general physical and mathematical field properties common to different transport processes This paper treats some fundamental aspects of this generalized fieldtheory and presents on that basis a new and general theory specifically applicable to the transport of electrons and hoioa in forward-biased non-tunnelling p-n junctions and heterojunctions The resulting unified conduction theory has been found to be very closely in agreement with experiment for 12 different types of p-n junctions and heterojunctions, which were made of semiconductor materials with energy gaps ranging from 0-3 to 2'8 ev In some experiments the forward current was varied over mora than 10 orders of magnitude In total, 46 experimentally measured V— l characteristics have been studi

Effect of plasma on propagation constant and radiations of a linear antenna with feed points displaced transverse to the antenna axis

Abstract: A theoretical study has been made to predict the effect of feed points displaced transverse to the axis of a centre-fed linear antenna immersed in a weakly ionized compressible warm plasma. A linearized theory is used such that the isotropic electron plasma is regarded as a single fluid continuum. A thin linear resonant antenna with its feed points displaced transverse to the antenna axis is used as a source of radiation and the propagation constant on it is taken to be general. General expressions for a field pattern factor and radiation resistance for both the electromagnetic and electroacoustic waves have been obtained. The case of a. half-wave dipole antenna is then treated, giving different values to the propagation constant. Some specialized results of other investigators are recovered under the condition that displacement is zero.

A new method of determining the electron density and collision frequency in plasma

Abstract: An analysis of the propagation phase constant β of a T.E.M. wave in plasma is made introducing a new factor wo that is proportional to the elastic restoring force on an electron in the space charge region under the influence of the electric field. From the experimental determination of β pin the anomalous dispersion region, the electron density Nc and the collision frequency v are obtained.

The calor-electric effect in atmospheric flame plasmas at thermodynamic equilibrium†

Abstract: Out of the theories proposed by earlier workers, the calor-electric effect is found to be more satisfactorily explained by the theory of the massive formation of negative ions near a water-cooled electrode. An attachment mechanism, operative below 100°c, is proposed to account for this massive formation. Calor-electric voltages up to 1–9 v are observed for the atmospheric CH4-O2 flame at thermodynamic equilibrium. A calculation method, utilizing double probe data, gives tho maximum expected value as 3 v under the assumption of complete attachment of electrons near a water-cooled electrode. The variation of the calor-electric voltage with the equivalence ratio of the flame shows a sharp maximum at stoichiometric proportions of CH4 andO2.

Current transport in isotype heterojunctions

Abstract: The emission theory and the diffusion theory of metal-semiconductor contacts have been generalized to describe current characteristics of abrupt isotype heterojunctions in the absence of interface states. One version of the generalized emission theory produces an expression for the current density previously given by Anderson. Another corrected version of this theory, however, results in a somewhat different expression. The generalized diffusion theory yields an expression for the current density that is fundamentally different from both these expressions. Numerical results are obtained for the particular case of nCe-nGaAs heterojunction under certain assumed doping levels. It is found that for certain conceivable conditions of the n-n hetcrojunction the diffusion theory predicts ohmie behaviour. Rectifying behaviour is predicted by the diffusion theory for other conditions and by the emission theory for all conditions of the hetcrojunction.

A study of the effect of the relative position of metal flanges on the radiation patterns of H-plane sectoral horn radiators†

Abstract: Results of an exhaustive experimental and theoretical investigation of the effect of position of metal flanges on the E-plane radiation patterns of H-plane sectoral horns arc presented. It has been established that the distance of the flange from the aperture of the horn has got great significance. The experimental values of the distances of different flanges giving sharp maxima and minima of the on-axis power are found to be in perfect agreement with the theoertical values estimated with the line-source theory suggested by earlier workers. For different positions of the flanges, the radiation patterns of the horns are plotted experimentally and they are compared with the theoretical ones computed using the line-source theory. Data for a good number of horns are presented for flanges of varying parameters and for a, wide range of frequencies.

Behaviour of silicon pn junctions at temperatures between 4-2 and 300° K†

Abstract: This paper presents the results of an investigation into the effect of lattice temperature on the breakdown voltage of silicon pn junctions. Measurements have been made over the temperature range 4-2-300° K using devices with nominal breakdown voltages from 8 to 13 v. Results show that the influence of temperature can be separated into three distinct temperature intervals. For temperatures greater than 100° K the carrier mean free path is the controlling factor of the ionization rate and causes the voltage to decrease with decrease of temperature. At low temperatures (less than 30° k) the breakdown voltage increases with cooling because freeze out of carriers in the base allows a significant voltage to be developed across this region. Calculations involving this voltage drop enable the field required for ionization of impurities to be evaluated. In the intermediate temperature range traps are observed by studying microplasma noise and these appear to influence the ionization rate. In addition to the break...

Calculation of drift velocity in silicon at high electric fields

Abstract: Drift velocity in n and p-type silicon is calculated using the Monto Carlo method to determine the current carrier distribution. Agreement with recent measurements for high field drift velocity is good. Carrier-lattice scattering rates for p-type silicon were determined from low field mobility versus temperature. D. Long's model was used for n-type silicon.

Twin-T feedback filters†

Abstract: Amplifiers with a single twin-T in the feeback path are analysed using root locus methods. A design approach has been suggested for realizing high-Q transistorised active filters resulting in a three-transistor configuration with a stable Q of 200. The behaviour of parallel and cascade configurations of two twin-Ts are studied with a view to realizing stagger tuned band-pass characteristics. It is found that frequencies of selection of the system are much different from the null frequencies of the two twin-Ts. This behaviour is explained using root locus techniques. The difference frequencies for various separations and loop gains have been tabulated. Finally it is concluded that stagger tuning can be realized only by connecting separate high-Q filters in cascade.

Resampling the output of switched networks

Abstract: The use of switches has given the engineers a new tool for modifying the characteristic of networks. Their use is usually that of a modulating process, i.e. to convert the signal wave into a series of amplitude-modulated pulses which are then further handled by a suitable network, usually a filter. The possibility of resampling the output has been investigated; it was found that the phase angle of the second sampler with respect to the first has a significant effect on both the phase and the magnitude of the time function that can be reproduced from the output of the second sampler.

Propagation constant and radiation field patterns of linear antennas in weakly ionized plasma

Abstract: In a series of studios of linear antennas immersed in weakly ionized plasma, the authors have investigated radiation properties of resonant and non-resonant antennas. In the present work, called part V of the series, radiation field patterns of resonant half-wave dipole and non-resonant optimized linear antennas immersed in weakly ionized plasma are evaluated for three different propagation constants of the current distribution. These are then compared with the corresponding standard patterns obtained in the vacuum. It is concluded that in plasma the fields contributed by the current distribution corresponding to β0 and βcare predominant and those corresponding to βp are practically negligible for the EM mode. However, for the P mode fields the situation is just the reverse.

Investigation of dense plasma by ion collection probe

Abstract: Assuming frozen flow conditions, the high pressure probe data is analysed to study the charge distribution in a mobility controlled boundary layer. The numerical results obtained for a confined argon plasma of 100-200 A at 1 atmosphere appear to be reasonable and self-consistent in the range studied. Also the charge distribution near the probe (∼10−3 cm) is extrapolated to estimate the plasma charge density in the centre of the column (0·5 cm from the probe), which is found to be in good agreement with the spectroscopic plasma density measurement.