Showing papers on "Depletion region published in 1968"

Surface Effects on Metal-Silicon Contacts

Abstract: Surface effects on metal‐silicon contacts have been studied in detail using gate‐controlled Schottky‐barrier diode structures. The ``excess'' forward and reverse currents at small and moderate bases, respectively, and low breakdown voltages usually associated with metal‐silicon contacts are clearly shown to be due to high fields near the corner region when the surface is accumulated. These currents can be eliminated and breakdown voltage increased by depleting or inverting the surface. By studying the diode characteristics when the surface is inverted, it is shown that the generation current in the depletion region often constitutes a significant part of the total reverse current and cannot in general be neglected.

Carrier generation-recombination in the space-charge region of an asymmetrical p-n junction

Abstract: The theory of generation-recombination in the space-charge region of a symmetrical p - n junction by Sah, Noyce and Shockley is extended to an asymmetrical junction. The role of junction asymmetry in determining the I–V characteristics of the junction is found to be enhanced by the capture asymmetry of donor-like (acceptor-like) recombination centers in an n + - p ( p + - n ) junction, but diminished in a p + - n ( n + - p ) junction. Where asymmetry effects are dominant at forward bias, the generation-recombination current is nearly independent of junction voltage, in contrast to the familiar exp( qV 2kT ) dependence predicted by the theory of Sah et al. Based on the presence of donor-like centers in an n + - p junction, a detailed discussion is given of the effects on the I–V characteristics at small forward bias due to variations in junction asymmetry, the capture asymmetry and energy level of the recombination centers. The theory is applied to InSb diodes, and previous analyses of generation-recombination current data on InSb diodes are examined.

Conductance of MOS transistors in saturation

Abstract: The output conductance of MOS transistors operating in the saturation region is studied theoretically and experimentally A simple physical model is described which accounts for the modification of the electric field in the drain depletion region near the Si-SiO 2 interface, due to the presence of the gate electrode The saturation conductance is shown on the basis of this model to be a sensitive function of the oxide thickness as well as the substrate impurity concentration Good agreement is obtained between theory and experiment over a wide range of device parameters The characteristics of lowly doped very-short-channel devices, which depart from this theory, are also discussed The departure is shown to be due to a "punch-through"-type phenomenon

Capacitance of Junctions on Gold‐Doped Silicon

Abstract: The capacitance of p+—n junctions and Schottky barriers on gold‐doped, n‐type silicon has been measured as a function of applied bias and time in the temperature range 205°‐255°K. The gold‐diffusion temperature was 1000°C. The time dependence of the capacitance has been examined on the basis of a model which assumes that the gold acceptor level has the same charge as in the bulk for some distance λ(t) from the edge of the depletion region. The analysis yields a value for the density of neutral acceptors in the depletion region of 1.1×1016 cm‐3, indicating that en»ep for the gold center. The energy associated with the capacitance time constant is 0.545±0.005 eV and the capture cross section σn is calculated to be 2.9×10‐15 cm2 at 250°K. Of a more general nature, a simple procedure is described for determining the contribution of slow‐responding deep levels to the capacitance of abrupt p—n junctions. This involves a plot of dV/d(1/C2) vs C, a relationship which was essentially derived by Goodman.

Hall mobility of electrons in the space-charge layer of thin film CdSe transistors

Abstract: Field- and Hall-effect measurements were performed on CdSe polycrystalline films at temperatures between −150 and +90°C. The mobility increased with carrier concentration over two orders of magnitude. This can be explained by the polycrystalline film model. It will be shown that in such a model a relatively small number of traps in the barrier region can have a profound influence on the onset of the enhancement-type field-effect conduction and its temperature dependence.

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.

Capacitance Recovery in Neutron-Irradiated Silicon Diodes by Majority and Minority Carrier Trapping

Abstract: Majority and minority carrier trapping has been studied in neutron-irradiated silicon diodes by transient junction capacitance recovery as well as by capacitance-versus-frequency and pulsed field effect techniques. After exposure to damaging radiation, trapping results in a transient time dependence of depletion layer width which may determine the survivability of depletion layer devices in a radiation environment. Majority carrier traps have been found in n-type neutron-irradiated silicon at Ec -0.36 eV and in p-type silicon at Ev + 0.30 eV. The capture cross sections for both types of traps are of the order of 10-15 cm2. Following a burst of damaging radiation, traps with unequilibrated charge exist with concentration roughly an order of magnitude larger than observed in equilibrium. These unequilibrated states relax slowly via the majority carrier band but quite rapidly when minority carriers are deliberately injected. Capacitance-voltage characteristics of neutron-irradiated junctions recovered by minority carrier injection show that recovery occurs only within a diffusion length of the metallurgical junction. Capacitance and lifetime recovery effects can be qualitatively interpreted in terms of the Gossick model for the disordered region spacecharge layer modified to include minority, as well as majority, carrier trapping. Recovery in this model is attributed to a shrinking of the disordered region space-charge layer.

Diffused diodes in silicon-on-sapphire

Abstract: The forward and reverse I–V characteristics of diffused diodes made in silicon grown epitaxially on sapphire have been measured. Silicon of doping density 4 × 10 15 to 6 × 10 17 /cm 3 p -type and 2 × 10 15 to 10 18 /cm 3 n -type have been used in these experiments. The forward conduction current of all diodes tested varied as exp ( qv /> nkT ) with n ≈ 1.7. Minority carrier lifetimes of the order 10 −10 sec have been inferred from the I–V data. The reverse currents were somewhat larger than predicted on the basis of currents generated in the space charge region but were reproducible from diode to diode. The temperature dependence of the diode currents was measured from room temperature to 200°C and followed the theoretical prediction. The variation of minority carrier lifetime with film thickness was measured, and the lifetime was found to increase as the silicon became thicker. Diodes produced by diffusion through the silicon to the silicon-sapphire interface were found to have minority carrier lifetimes about an order of magnitude lower than diodes not diffused to the bottom interface.

Different mechanisms affecting the inversion layer transient response

Abstract: The transient response of the MOS capacitance after the application of a large depleting voltage can be caused by three different mechanisms depending on the distribution of the electric field between the silicon and the oxide. The three different cases were distinguished by measurements of the temperature dependence and the voltage dependence of the relaxation behavior. Relaxation due to thermal generation of carriers prevails at low electric fields, relaxation via oxide states occurs at medium fields, and relaxation by avalanche effects predominates at high fields. From the case where thermal relaxation is predominant the effective lifetime of minority carriers in the depletion region and the surface recombination velocity could be determined. At low temperatures (&sim100°K) where most frequently no relaxation occurs in the dark, light-induced relaxation phenomena were studied. Only light with energies larger than the Si band gap causes relaxation.

The charge distribution in high-speed transistors

Abstract: A self-consistent scheme of subpicocoulomb charge measurement and two-dimensional, transport analysis has been used to calculate the distribution of charge in high speed (3-7 GHz) Ge and Si transistors. This scheme carefully measures total stored charge and calculates the mobile charge stored in the two-dimensional base and collector space charge regions. Storage in the emitter space charge layer is obtained by subtraction of calculated charge from measured charge. The conclusions of this study are" (1) The majority (as much as 80%) of the mobile charge is stored in the emitter; (2) 30-50% of the remaining charge is injected through the emitter side-wall and stored in the remote base region; (3) overall transit time is dominated by low field mobility regions -- thus Johnson's fundamental limitations do not apply, and the transit time of state-of-the-art devices continues to reflect the low-field mobility of the material ( \micro Ge ∼ 3 × \micro Si).

Semiconductor device and a method of making the same

Abstract: Semiconductor device of the field effect transistor type including a first semiconductor region of one conductivity type, a second semiconductor region abutting the first region and containing at least one polycrystalline region and one single crystal region, the polycrystalline region having a conductivity type opposite to that of the first semiconductor region thereby forming a PN junction therealong, and a third semiconductor region formed in the second semiconductor region.

A proposed punch-through microwave negative-resistance diode

Abstract: A new microwave negative-resistance diode is proposed. The diode is similar to the Read diode insofar as the negative resistance is partially due to the finite transit time of carriers flowing through a depletion region. Unlike the Read diode, however, the carriers are injected into the depletion region by punch through rather than by avalanche. The resulting device is therefore expected to have a considerably better noise performance than the Read diode. The paper first explains qualitatively the punch-through operation of the proposed device and contrasts it with similar structures proposed earlier by Read and by Shockley. The large signal admittance of the punch-through diode is then obtained by using a sharp pulse approximation of the injection process. A device Q of -15 is calculated. Considering the device as a microwave oscillator, it is found that conversion efficiencies of the order of 20 percent should be possible. Estimates of the upper bounds on the microwave power are given. The paper concludes with a detailed account of design considerations for the device. Numerical designing examples for the frequency range of 1 to 5O GHz are given.

Transport of Electrons in a Strong Built‐in Electric Field

Abstract: The problem is discussed of the transport of electrons in the presence of a strong field due to fixed space charges, as in the depletion region of a p‐n junction. It is found that the effective mobility, for small departures from equilibrium, is equal to the chordal hot‐electron mobility which would result if the strong field were applied by external means.

Transfer functions of imaging mosaics utilizing the charge storage phenomena of transistor structures

Abstract: Silicon phototransistors operating in the integration mode have been used in light detection and imaging systems. A solid-state imaging system employing a monolithic mosaic of 12 800 n-p-n phototransistors has been developed. An analysis of the integration mode of operation of a silicon phototransistor is presented. The analysis employs a simplified equivalent circuit of a phototransistor. Three different cases are analyzed; each case differs in that the length of the readout cycle is changed. The solution to all three cases gives an output voltage directly proportional to the ratio of light plus leakage generated charge to the base-collector junction depletion layer capacitance. Analysis of phototransistor operation in a mosaic where interactions with the other phototransistors in the array are accounted for is presented. Discussion concerning the parasitic capacitances due to readout switches is given for the particular mosaic design employed.

Response of Lithium-Drifted Silicon Radiation Detectors to High Energy Charged Particies

Abstract: The measured response characteristics of lithium-drifted silicon radiation detectors at 295°K and 79°K are presented for protons with energies from 315 to 3.5 MeV; for positive pions with energies from 50.2 to 206 MeV; and for electrons with energies from 265 keV to 767.2 MeV. Analysis of the energy loss spectra confirms that the energy is being deposited by the protons and pions in the silicon purely through collision losses, whereas it appears that the silicon absorbs additional energy lost by the high energy electrons through interaction of the bremsstrahlung radiation in the depletion region. The charge collection efficiency determined by gamma rays is shown to agree with the charge collection efficiency determined by minimum ionizing particles. Nonlinear effects caused by unequal electron and hole trapping lengths and surface effects lead to reduced charge collection efficiencies for low energy electrons which do not completely penetrate the detector depletion region, in agreement with theory and with observations in the X-ray region. Apparent recombination effects also lead to reduced charge collection efficiencies at low fields or for protons with energies below about 100 MeV under constant bias conditions. The present data support the conclusion that the charge conversion factor ? at any one temperature is constant to within 1% for electrons, pions and protons over the entire energy span measured.

Neutron Radiation Damage in Silicon Transistors

Abstract: In the investigation of base and collector current as a function of the emitter-to-base voltage, previous studies have shown that neutroninduced base current has components originating in the emitter space charge region as well as the neutral base region. This study shows that while the low injection level neutron-induced base current is dominated by the space charge component, the high injection behavior appears to be controlled by recombination in the neutral base region. Additional experiments performed in special tetrode transistors and van der Pauw-type samples indicate that changes in collector current are dominated by recombination in the neutral base, while changes in base doping and mobility have only a secondary effect. These conclusions are reached from experiments on transistors with a ring emitter, on tetrode-type test transistors, and on special Hall-effect devices, and by a detailed analysis of the emission crowding characteristics of a "ring-dot" geometry device.

Schottky barrier atomic particle and x-ray detector

Abstract: A solid-state atomic particle and X-ray detector comprising an N-type semiconductor crystal of high atomic number, coated with a metallic film of low atomic number. By making the metal-tosemiconductor interface abrupt, a Schottky barrier-type junction is produced. Atomic particles or X-rays can easily penetrate the metallic film but are absorbed in the semiconductor near the interface, producing electron-hole pairs in the depletion region. Holes which diffuse beyond the depletion region give rise to a current indicative of detection of X-rays or atomic particles.

Bulk oscillation by tunnel injection

Abstract: In this paper a fundamental oscillating frequency of 129 GHz is obtained with a GaAs pn junction diode in which avalanche current co-exists with tunnel effeetl These GaAs diodes are produced by the solution growth method. Oscillations are seen when the diodes are pulsed into reverse bias. The low breakdown voltages observed require consideration of both tunneling and avalanche current components. In 1958, the negative resistance diode oscillator using both the avalanche phenomena and transit time effect in pn junction has been proposed by W. T. Read and by J. Nishizawa et al independently, and a large number of experimental reports concerning the above oscillator operating at microwave and mm wave frequencies have been published. It is necessary especially for obtaining oscillation with good efficiency in mm wave region that the transit time of the tunneling or avalanche injecting region be very small compared with the transit time layer width. In pn junctions if the depletion layer is of the order of the mean free path of carrier ionization, injection current flows by tunneling and not by avalanche. Therefore, by our experiment higher frequency oscillation is expected by combining tunnelling injection with transit time. Moreover the tunnelling injection can reduce the applied voltage for the oscillation and 129 GHz can be obtained with only 8 volt. The efficiency is expected to be increased with a pnin structure which is now being studied.

Radiation and Annealing Characteristics of Neutron Bombarded Silicon Transistors

Abstract: Operating a silicon planar epitaxial transistor in the inverse configuration allows one to demonstrate clearly the importance of the neutron-induced base current component and its degradation of the emitter efficiency, and, because of the much larger depletion layer, to compute a volume dependent damage constant applicable to all silicon p-n junctions. The importance of minimizing the absolute change versus relative change in radiation hardening studies is clearly illustrated. Surface effects were found to be significant for transistors mounted in gas-filled cans. The diffusion potential was predicted, on theoretical grounds, to vary with neutron fluence, and the theory was experimentally confirmed. Isochronal and isothermal annealing data were obtained for the inverse configuration and from these data, it is concluded that the neutron-induced defect centers are field dependent.

Method for making a hot carrier pn-diode

Abstract: Disclosed is a Schottky barrier or hot carrier diode and process for making same wherein a diffused PN junction and a Schottky barrier junction are both formed in a body of semiconductor material. The diffused PN junction is formed by first diffusing an impurity through an opening in a diffusion mask and into one surface of the semiconductor body to form PN junction. Next, a large central portion of the region formed by the above diffusion is removed by etching or cutting, leaving unaffected by the etchant only that portion of the diffused region underlying and adjacent to the diffusion mask on the surface of the semiconductor body. The latter portion of the diffused region forms a relatively small area diffused PN junction. Finally, a Schottky barrier junction is formed in the etched out area of the semiconductor body, and the diode including the diffused and Schottky barrier junctions has a near-ideal current-voltage characteristic and still maintains its fast recovery time.

Comparison of surface and bulk effects of nuclear reactor radiation on planar devices

Abstract: Surface effects of nuclear reactor irradiation are separated from bulk effects, and their relative importance compared. It is shown that the rates of change of surface recombination velocity and lifetime with dose are such that at high doses surface effects have an insignificant influence on p-n junction recombination-generation currents compared to bulk effects. In particular, the degradation of current gain at low collector currents in reactor irradiated bipolar transistors is shown to be the result of increased recombination in the bulk rather than at the surface of the emitter-base depletion region, in contrast with the case of ionizing radiation alone.

Integrated circuit having lightly doped expitaxial collector layer surrounding base and emitter elements and heavily doped buried collector larger in contact with the base element

Abstract: An integrated circuit is provided in which a heavily doped buried layer within the collector of a transistor extends into contact with the base thereof to form the major portion of the collector-base junction. The buried layer enhances the current gain bandwidth by minimizing the width of the collector-base depletion region and the shift thereof into the collector for high-current densities. The effects of capacitances at the collector-base junction and at the junctions of resistors and isolating walls adjacent the transistor are minimized by a lightly doped epitaxial layer within the collector of the transistor.

Monolithic integrated circuit structure

Abstract: An annular PN junction in conjunction with a relatively high resistivity substrate enables improved means for isolating functional elements in a monolithic semiconductor integrated circuit. In a semiconductor wafer, localized emitter zones and collector zones extend to a common depth from the surface of the wafer. The collector zone is annular in shape and encloses laterally the emitter zone. The resistivities and spacings of the regions in the wafer are such that with the annular PN junction reverse-biased, the depletion region therefrom extends completely underneath the material enclosed by the annular zone and thereby provides electrical isolation for a functional element in the enclosed material.

A unified model of the oxide cathode which gives prominence to the role of localized surface states on small crystals

Abstract: A unified model of the oxide-coated cathode is suggested which attempts to combine the essential features of Nergaard's single-crystal model with those of Loosjes and Vink's pore-conduction model. The most important characteristic of the new model is that it regards the cathode as consisting of many small crystals (1 μm) whose surface properties predominate over their bulk properties. A consideration of the effects of localized impurity levels on such small crystals shows that they could produce a depletion layer which would have a depth varying from 10% to 100% of the mean size of the crystals. The band bending caused by these localized levels could also raise the work function of the crystals by amounts ranging from 005 to 1 v. This surface depletion layer offers an alternative hypothesis to the usual donor depletion layer, which had been assumed to be caused by electrolysis in the single-crystal model. The effects of these two types of depletion layer probably supplement each other in the decay of pulsed emission currents from the cathode. The surface depletion layer would predominate in a well-activated cathode, but field penetration effects would be important if it were poorly activated or in a high electric field. A large part of the activation process, and probably the whole of the process of the poisoning and recovery of a cathode's emission, can be accounted for simply in terms of changes in the concentrations of surface states.

Computer solution of depletion and accumulation layers and analysis of abrupt n - n heterojunctions

Abstract: The digital computer solutions of depletion and accumulation layers are given for doping levels of 1014, 1015 and 1016 cm−3 using Ehrenberg's approximation. The interface values of voltage against electric field are plotted and the depletion layer solutions are compared with the parabolic approximation, which is found to give only about 1% error for calculation of interface values although it is not so good for obtaining the actual barrier shape. A new technique is presented for analysing abrupt n-n heterojunctions and the (C, V) characteristic is analysed in detail. The plot of C−2 against V is in fact linear, in reverse bias only, although the simple formula C2=(eNd)/2(Vd-V) is not applicable.

Semiconductor device including a metal layer overlying the junction area

Abstract: A high speed high current switching device is described wherein a metal-to-semiconductor rectifier element is selectively placed within the sphere of influence of a spatially variable space charge region of a semiconductor junction formed between semiconductor materials of opposite conductivity. Several embodiments are described.