Showing papers in "Solid-state Electronics in 1962"

An investigation of surface states at a silicon/silicon oxide interface employing metal-oxide-silicon diodes

Abstract: A new solid-state device, the M-O-S diode, of which an oxidized silicon surface is an integral part, is introduced, and a theory for its operation in the absence of surface states is obtained. The capacitance of this device may be considerably more voltage sensitive than that of a p-n junction. The existence of surface states with non-zero relaxation times is introduced into the theoretical model. It is shown that the states may increase the capacitance of the device, as well as affect the proportion of applied voltage which appears across the silicon. A small-signal equivalent circuit is derived which includes the effect of the surface states. It is also shown that a comparison of the theoretical capacitance vs. voltage curve without states and a measured high-frequency capacitance vs. voltage curve may be used to obtain the distribution of all states, regardless of their time constants. Results are given of measurements and calculations on two M-O-S diodes having different surface treatments before oxidation. Both surfaces have a total density of about 3 × 10 12 states/cm 2 . In both cases, the distribution of states is continuous and has its highest peak about 100 mV above E F (0), the position of the Fermi level at the silicon surface if there is no voltage drop across the silicon The time constants of the states extend from 10 −8 sec to longer than 10 −2 sec. There is a tendency for states located at deeper energy levels to have longer time constants, but some of the states in the high density of states above E F (0) have long time constants. The distribution of time constants with energy level is somewhat different for the two surfaces. A comparison is made between the distribution of states obtained here with the distribution reported by others working in the field. The results are similar in density and location of the peaks of the distribution reported here, but differ in that some other sources report a discrete distribution.

Experiments on Ge-GaAs heterojunctions

Abstract: The electrical characteristics of Ge-GaAs heterojunctions, made by depositing Ge epitaxially on GaAs substrates, are described. I–V and electro-optical characteristics are consistent with a model in which the conduction- and valence-band edges at the interface are discontinuous. The forbidden band in heavily doped (n-type) germanium appears to shift to lower energy values.

Rapid zinc diffusion in gallium arsenide

Abstract: It is assumed that zinc acts as a donor when in interstitial positions in gallium arsenide, although it is an acceptor in its normal gallium substitutional positions. When the zinc doping is very heavy, a small fraction of the zinc should go into these donor interstitial positions and these should diffuse very rapidly thereby being dominant in the over-all diffusion process. Plausibility arguments are given for interstitial diffusion, and a critical test is suggested. In the case of tunnel diodes the deterioration due to interstitial impurity diffusion should be most rapid, as compared to slowest for substitutional diffusion, when the diode is forward biased.

Constitutional supercooling during crystal growth from stirred metls. III. The morphology of the germanium cellular structure

Abstract: The morphology of the germanium cellular structure obtained by growing crystals under conditions of constitutional supercooling has been examined using metallographic techniques A study of the growth striae delineated by etching shows that the cellular interface is composed of an array of small {111} planes The particular {111} planes which predominate are those which lie nearest the plane of the interface If the plane of the interface is itself a {111} plane, the interface becomes faceted with macro-steps on it The size and distribution of the cells is shown to depend on the fluid flow and the gradient of constitutional supercooling adjacent to the interface Evidence is presented which indicates that the liquid is trapped at intervals in the re-entrant corners formed by the {111} planes and that this liquid subsequently climbs down the crystal by temperature gradient zone melting It is demonstrated that, in order to avoid transient cell formation during growth from heavily doped melts, a high stability against growth rate fluctuations is required

Rectification and space-charge-limited currents in CdS films

Abstract: The electrical properties of CdS films have been studied as a function of preparation. Films have been obtained having resistivities from 0·1 to 108 Ω-cm and Hall mobilities from 1 to 30 cm2V−1 sec−1. Rectifiers have been constructed from these films which have shown rectification ratios of 106 with reverse breakdown voltages ranging from 5 to 15 V. Some of the diodes, prepared from high resistivity CdS, exhibit a square law dependence of current on voltage, typical of space-charge-limited currents (SCLC). The onset of the square law current is accompanied by a rapid decrease in the capacitance of the diode. The small effect of the large trap densities on the magnitude of the SCLC cannot be accounted for by the present theory.

Accurate solution of an idealized one-carrier metal-semiconductor junction problem

Abstract: An accurate digital-computer solution is presented of the differential equations describing an idealized metal-semiconductor junction. Mobile charges of negative sign only are considered which arise from a uniform, fixed-donor charge distribution. The situation is similar to that considered earlier by W agner , S chottky and S enke , and accurate results for the static current-voltage characteristic and distance dependence of field, electrostatic potential, and quasi-Fermi-level potential are compared with previous approximate results. Primary attention is devoted to a structure involving one ohmic and one barrier electrode separated by a fixed distance, but that involving two barrier electrodes a fixed distance apart is also investigated. The problem is idealized by omitting trapping, image effects, tunneling, recombination, breakdown and hot-electron effects. Earlier approximate treatments are rather inaccurate in their predictions of the space dependence of various quantities but are quite close in their current-voltage predictions, even in the forward-bias direction of current flow. The results for a fixed length of material between electrodes are compared with those of the more usual approximate analyses which pertain to a variable-length barrier region alone. The influence of the fixed length, which corresponds to the experimental situation, is large, under some conditions, on current-voltage relations, resistance and on the forward and reverse differential capacitance of the system.

Forward characteristics and efficiencies of silicon solar cells

Abstract: Forward currents in commercial solar cells show an exponential dependence on the forward voltage as exp (qV/AkT) with A ⋍ 3. This factor 3 in the exponent cannot as yet be explained satisfactorily. Experiments indicate that this strange forward characteristic is not an over-all property of the entire cell, but comes from localized regions of the junction area, preferentially at the cell edges. Heat treatments at temperatures low enough to exclude appreciable donor and acceptor diffusion produce significant changes in the characteristics. The results are interpreted in terms of impurities which are either dissolved or precipitated. These experiments show that commercial solar cells contain unnecessary defects which cause their strange characteristics and lower their efficiencies.

Light emission from forward biased p-n junctions in gallium phosphide

Abstract: Deep recombination centers in homogeneously doped and as-grown single crystals of GaP have been studied by Hall effect, photoluminescence and absorption spectra. These centers act as radiative recombination centers for injected carriers in forward-biased p-n junctions doped with the same impurities. One of these levels, a deep donor, 0·4 eV below the conduction band, is present in most of the undoped crystals and is very likely associated with substitutional oxygen as a residual impurity in the 1–5 × 10 18 atoms/cm 3 range. In several specific cases this center determines the rate of recombination of minority carriers in the junction transition region. The non-radiative decay from this level in comparison with the radiative lifetime of the center (10 −5 sec) determines the quantum efficiency of the luminescent process (10 −2 at 80°K) and the light-emission decay time (10 −8 sec at 300°K). Other deep radiative recombination centers are due to impurities (S, Se, Te, Cu, Zn, Mg and Cd) which have interacted with the deep-donor center. Their effect upon the luminescent processes has been correlated with an equilibrium between substitutional oxygen and interstitial oxygen. A third type of emission giving rise to fairly narrow lines (0·01 eV at 20°K) is most probably due to molecular aggregates of interstitial oxygen with host lattice atoms. Finally, direct band-to-band recombination luminescence is observed, although it is relatively inefficient (10 −8 at 300°K).

Diffusant impurity-concentration profiles in thin layers on silicon

Abstract: An etch-sectioning method is combined with sheet-resistance measurements to give routine analyses of thin layers, containing in-diffused boron or phosphorus, on silicon, with either a polished or a lapped finish. The resultant impurity distribution confirms previous work that there is wide deviation from a complementary-error-function distribution. The behavior near the surface suggests some physical differences from diffused samples evaluated by other groups.

The space-charge-limited dielectric triode

Abstract: The design and operation of the space-charge-limited dielectric triode are described with parameters representative of mobile electrons in gallium arsenide. It is proposed that the triode is fabricated as a layer structure with the epitaxial techniques developed for the preparation of conventional semiconductor junction devices. The operating mechanisms of the triode are discussed and indicate that pentode-type characteristics over a very wide frequency range are obtainable. The dielectric triode is compared with the semiconductor transistor on the basis of their respective charge control parameters. The triode has small input capacitance and short transit time; the transistor has large input capacitance and long transit time. Compared with the transistor, the triode offers operation at low noise power levels and much reduced sensitivity to temperature changes. It is concluded that space-charge-limited solid-state devices are basically suited to electronics applications, whereas diffusion-limited solid-state devices are basically suited to power applications.

Power gain of transistors at high frequencies

Abstract: The power gain and ƒmax are calculated in general for junction transistors with any impurity distributions. It is shown that the power gain will fall by 6 db/octave for all junction transistors. The general formula for ƒmax can be related to the common-emitter current gain cut-off frequency. At a critical current, a maximum in power gain is achieved in drift transistors. This critical current is the same for power gain and for high-frequency common-emitter current gain.

A microwave Adler tube

Abstract: A description is given of an Adler tube operating at 2700 Mc/s. This is a sealed-off version of a previously described demountable experiment at 4000 Mc/s. Gain of 24 dB can be obtained and the double channel effective input noise temperature is 96°K (noise factor 1·24 dB), as measured at the input terminal of the tube. By correcting for circuit losses the effective beam temperature is given as 62°K. A band-width of 10 Mc/s is obtained at points where the minimum noise temperature is doubled. Improvements which may reduce the noise temperature even further are described.

Hot-electron emission from semiconductors

Abstract: This paper describes the emission of high-energy electrons from p-n junctions in silicon and silicon carbide. The distribution of emitting areas was studied by means of a fluorescent screen. It was proved that in silicon the emission pattern is closely related to the microplasma pattern in the junction and that electrons are emitted across the thin n-type surface layer. In silicon carbide this layer was too thick and only peripheral emission was observed. The relative merits of very shallow (100 A) silicon junctions and of silicon carbide junctions are discussed.

p-n-junction photovoltaic effect in zinc-doped GaP

Abstract: The p-n-junction photovoltaic effect in Zn-doped GaP was studied as a function of various parameters. The spectral sensitivity, the temperature dependence of the short-circuit current and the open-circuit voltage are discussed. In addition to the intrinsic effect an extrinsic photovoltaic effect was found. Arguments are given to show that the extrinsic response is not an electrode effect, but is clearly correlated with the specific dope introduced into the GaP bulk.

Scheinwiderstand und Sperrkennlinien von Silizium-p-n-Übergängen mit Oberflächeninversionsschicht

Abstract: Zusammenfassung Das Ersatzschaltbild eines p-n-Uberganges mit Oberflacheninversionsschicht ist eine Kette von endlicher Lange mit infinitesimalen RC-Gliedern. Aus Scheinwiderstandsmessungen wurde die Dicke der Raumladungszone, die Channelleitfahigkeit und daraus die gesamte Oberflachenladung und das Oberflachenpotential bestimmt. Bei einem Gleichrichter mit p-sp-n-Struktur bedeckt die Inversionsschicht die gesamte Oberflache des schwach p-leitenden Siliziums. Hat ein solcher Gleichrichter eine Storung unter der Oberflache, so wachst die Durchbruchsspannung mit wachsender Oberflachenladung, d.h. mit starkerer Auspragung des Channels.

Die galvanomagnetischen eigenschaften von InSb bei hohen magnetfeldern

Abstract: Der Hallkoeffizient von eigenleitendem und stark n -leitendem InSb ist bei Zimmertemperatur bis 150.000 G unabhangig von der magnetischen Induktion. Er nimmt bei schwacher n -Dotierung mit dem Magnetfeld zu, bei geringer p -Dotierung ab. Die Locherbeweglichkeit sinkt von etwa 700 cm 2 /V-sec ohne Feld auf 610 cm 2 /V-sec bei 150.000 G. Die Eigenleitungskonzentration von InSb ist bei Zimmertemperatur unabhangig vom Magnetfeld. Von 10 G bis 150.000 G gilt fur das Leitungsband: R n = −1/en.

Zener breakdown in alloyed germanium p+-n junctions

Abstract: An experimental study has been made on the breakdown characteristics of alloyed germanium p + -n junctions. Breakdown characteristics are found to be controlled by the Zener effect when a specific resistivity of the n -type base is lower than 0·14 Ω-cm (corresponding to the breakdown voltage of 19 V), whereas avalanche-type breakdown is observed in the case that when base resistivity is higher than that value. Between Zener and avalanche regions, distinct differences of such breakdown properties as temperature dependency of the breakdown voltage, current multiplication phenomena, generation of microplasma at low temperature and dependency of breakdown voltage on impurity concentration of the base crystal are observed. Samples used throughout these experiments are defectless, alloyed junctions having sharp breakdown characteristics about which the author reported in another paper.

Impurity-induced pipes through diffused layers in silicon

Abstract: An investigation has been made of the origin and prevention of pipes through diffused layers in silicon. It was found that the type of pipe most frequently observed, results from diffusion of dopant from a speck of contamination on the surface. Considerable enhancement in the number of pipes was found when silicon slices were exposed to laboratory ambient prior to diffusion. The same effect could be obtained by very short contact with a P 2 O 5 aerosol at room temperature. Slices exposed to P 2 O 5 aerosol for more than five seconds showed a continuous n -type film on the surface after diffusion. In a heat treatment experiment the diameters of pipes were shown to grow with the square root of time, a behavior that agrees with theoretical calculations, assuming superposition of a planar and a spherical diffusion, both of the Gaussian type. A number of different pipe shapes can be expected, dependent on the ratio of surface concentration to the product of diffusion coefficient and time. Incidence of pipes has been minimized by special attention to cleanliness in handling slices and by preventing exposure to dust in the laboratory atmosphere during the steps of the diffusion process.

The capabilities of cassegrain microwave optics systems for low noise antennas

Abstract: The maximum available range of a space-to-ground communication system is analyzed from the standpoint of the receiving ground antenna. The range, or signal-to-noise ratio of such a system is influenced by the aperture efficiency and noise temperature of the antenna. The aperture efficiency can be increased and the noise temperature decreased if the feed pattern f; (ψ) is unity up to the aperture angle of the paraboloid and is zero beyond this angle. The ideal feed pattern can be approximated by a Cassegrain type primary reflector if the aperture size of the secondary reflector is large. Theoretical and experimental results are provided to determine the optimum dimensions of such an antenna.

Experiments on the metal-interface amplifier

Abstract: Metal-interface amplifiers of the kind described by S pratt , S chwarz and K ane have been fabricated with thin Al and Al 2 O 3 films and a thick Au emitter Grounded-base and grounded-emitter collector characteristics are similar to those of an n-p-n junction transistor Power gain of the order of 100 has been obtained from these structures at room temperature and at a frequency of 1 kc/s Experiments involving variations in Al film thickness, and variations in oxide thickness have been performed Several anomalous features of the device, such as the decrease in tunneling resistance with increasing Al film thickness, and the decrease of α and β under dc conditions, are reported Measurements of two- and three-terminal transfer characteristics have been examined in order to elicit information concerning the mechanism responsible for power gain The measurements and experiments have been evaluated with a view to establishing whether a hot-electron or depletion-layer transistor model is effective In order to accommodate the depletion-layer transistor model of H all , pinholes ranging from a few hundred angstroms to several microns have been incorporated into the structure The measurements and experiments reported here suggest that there is merit in H all 's proposed model While a major portion of the current transferred from Au to Ge probably takes place by means of injection into the space-charge region of the Ge, none of the measurements reported rules out the possibility that a small portion of the current may be carried by hot electrons

Effects of surface heat transfer on the performance of a thermoelectric generator

Abstract: Analytical solutions are given for the steady-state temperature distribution, power output, and efficiency of a thermoelement which is used in a thermoelectric power generator. The longitudinal surface of the thermoelement is divided into three regions. The first region is exposed to convection with the environment at the cold junction; the second region is thermally insulated; the third region is exposed to convection with the environment at the hot junction. The relative sizes of the three regions are variable. The solutions are useful for predicting the performance of thermoelectric power generators and for showing the improvements in performance that can be gained through the use of surface heat transfer. It is shown that substantial increases in the power output can be gained if the thermoelements are exposed to surface heat transfer. It is possible to use surface heat transfer to reduce greatly the amount of fin surface needed at the hot and cold junctions. A numerical example is presented in which no fins are used at the hot and cold junctions; it is shown in this example, that, by using surface heat transfer, 97 per cent of the maximum theoretical output can be achieved.