Showing papers on "Doping published in 1970"

Electron tunneling and contact resistance of metal-silicon contact barriers

Abstract: The contact resistance of Al and Pt on n -type Si over a wide range of doping concentrations (10 18 → 2 × 10 20 cm −3 ) has been measured at both room temperature and liquid nitrogen temperature. These experimental results are compared with theoretical calculations based on a model with electron tunneling through the potential barrier at the interface as the dominant mechanism of current flow. Good agreement is found. It is hoped that this physical model can be used as a guideline in developing ohmic contacts for various semiconductor devices.

Carrier transport across metal-semiconductor barriers

Abstract: Carrier transport across metal-semiconductor barriers has been studied theoretically and experimentally to give a generalized and quantitative presentation. The thermionic and tunneling processes have been analyzed in terms of accurate quantum transmission coefficients. The effects of image-force lowering, temperature, and two-dimensional statistical variation of impurity concentration have also been incorporated in the theory. Theoretical results give a description of the current transport, due to combined effect of tunneling and thermionic emission over a temperature range from essentially absolute zero to the highest practical temperatures, and over doping densities from 1014 cm−3 to complete degeneracy. An interesting result of the analysis is the existence of a minimum in the saturation current density Js near 1016 cm−3; the current density rises slightly at lower dopings because of enhanced transmission coefficient for thermionic emission and increases drastically at higher dopings because of tunneling. For example for PtSiSi system at 300°K with a barrier height of 0.85 eV, Js is 80 nA/cm2 at 1014 cm−3, reaches a minimum of 60 nA/cm2 at 1016 cm−3, then rapidly increases to 103 A/cm2 at 1020 cm−3. In the high doping range the average saturation current density is considerably increased by the effect of two-dimensional impurity variation. The room-temperature transition doping for breakdown in metal-silicon systems occurs at 8×1017 cm−3; for lower dopings the breakdown is due to avalanche multiplication, and for higher dopings it is due to tunneling of carriers from the metal Fermi level to semiconductor bands. The metal-silicon diodes were fabricated by planar technology with guard-ring structures to eliminate edge effects. Extensive experimental studies, including current-voltage, capacitance-voltage, and photoelectric measurements covering the doping range from 1014 to 1020 cm−3 and the temperature range from 77°K to 373°K, gave good agreement with theoretical predictions.

Concentration and Behavior of Carbon in Semiconductor Silicon

Abstract: The concentration of carbon in semiconductor silicon and the behavior of carbon in the fusion and crystallization of silicon have been studied by the use of charged particle activation analysis. The solubility of carbon in solid silicon has been found to be or slightly less at the melting point, and the equilibrium distribution coefficient of carbon between solid and liquid silicon has been determined to be . Carbon content over the above solubility value has seldom been observed in silicon single crystals produced by modern industrial techniques. The content appears to depend more on the growth conditions of the single crystal than on the chemical purification method. The phase diagram of the C‐Si system in the extremely low carbon concentration range is given, together with a discussion of the kinematics of the carbon behavior in zone melting. Also, a new technique for studying the evaporation of carbon from the silicon melt is shown.

Capacitance Energy Level Spectroscopy of Deep-Lying Semiconductor Impurities Using Schottky Barriers

Abstract: The capacitance‐voltage (C‐V) relationship of a Schottky barrier diode is predicted for an energy distribution of impurity levels having spatially uniform concentration in an n‐type semiconductor. The model applies for forward and reverse bias voltages at modulation frequencies near dc and at modulation frequencies at which one or more of the deep doping levels cannot respond. Effects of partial ionization of impurity species and the effect of electrons in the depletion region are considered. It is predicted that the diode [d(1/C)/dV] versus V relationship exhibits sharp minima when the barrier height minus the applied bias is equal to the energy level relative to the conduction band edge of any of the predominant deep‐lying impurities in the semiconductor. The way in which deep lying impurities consequently affect a C‐V impurity profile analysis is discussed.

Germanium‐Doped Gallium Arsenide

Abstract: Germanium‐doped GaAs crystals were grown on GaAs seeds from Ga solution. The properties of the Ge‐doped GaAs layers were examined by Hall effect measurements from 20° to 400°K and by photoluminescence measurements between 12° and 300°K. It was found that Ge‐doped GaAs is always p‐type when grown at 900°–875°C from Ga solution containing 56 at.% or less Ge. The temperature dependence of the Hall coefficient and the photoluminescence experiment indicated an acceptor energy level of 0.035 and 0.038 eV respectively. It was also found that at least 85% of the Ge was present as an acceptor in the GaAs crystals when the growth solution contained two atom percent or less Ge.

High frequency bulk semiconductor amplifiers and oscillators

Abstract: Stable high frequency oscillating and amplifying devices are prepared from bulk semiconductor materials which have a positive differential conductivity at relatively low frequencies and a negative differential conductivity in some ranges of relatively high frequencies. The materials used are further characterized in that there is charge carrier transfer or population redistribution from a lower mobility band or low mobility impurity level to a higher mobility band, an effect opposite to that of Gunn effect devices. Materials suitable for the devices of this invention may be selected from a representative group of suitably doped III-V compounds, for example, N-type InSb, N-type alloys of the form InxGa1 xAs, where 0.53

Doped semiconductor electrodes for mos type devices

Abstract: The threshold voltage required to invert an MOS device is both shifted and selectively controlled by using appropriately doped semiconductor material as the gate electrode.

Ionic conduction of pure and doped CaF2 and SrF2 crystals

Abstract: The ionic conductivity of pure as well as NaF- and YF3-doped CaF2 and SrF2 crystals was investigated between room temperature and 900°C. The absorption of the crystals was measured before and after X-ray irradiation. The results are in accordance with an anti-Frenkel disorder. While for CaF2 only the formation energy of the defects, their activation energy of the mobility, and their association energy for the bonding to an aliovalent foreign ion could be obtained, in the case of SrF2 it was also possible to determine the density of the anti-Frenkel defects, their jump frequencies and mobilities as well as the entropy changes associated with the activation processes. In addition, the oscillator strength for the 213 nm band of O− in SrF2 could be calculated. Die Ionenleitfahigkeit reiner und mit NaF bzw. YF3 dotierter CaF2- und SrF2-Kristalle wurde zwischen Zimmertemperatur und 900°C untersucht. Die Messung der Absorption der Kristalle erfolgte vor und nach Rontgenbestrahlung. Die Ergebnisse stehen mit einer Anti-Frenkel-Fehlordnung in Einklang. Wahrend fur CaF2 nur die Bildungsenergie der Defekte, deren Aktivierungsenergie der Beweglichkeit und ihre Assoziationsenergie fur die Bindung an ein anderswertiges Fremdion bestimmt werden konnten, war es bei SrF2 zusatzlich moglich, die Dichte der Anti-Frenkel-Defekte, deren Sprungfrequenzen und Beweglichkeiten sowie die mit den Aktivierungsprozessen verbundenen Entropieanderungen anzugeben. Auserdem konnte die Oszillatorenstarke fur die 213 nm-Bande des O− in SrF2 berechnet werden.

Covalency and Electronic Structure of Cu2+ in ZnF2 by EPR

Abstract: With the aid of computer techniques, including a laboratory automation system, accurate computer simulation, and an accurate calculation method, the EPR spectrum of copper doped in zinc fluoride has been analyzed. The observed g values led by a new method to a determination of the coefficients of the Kramer's doublet. Copper hyperfine structure verified these values and fluorine transferred hyperfine structure gave a measure of covalency. The fractional orbital occupation showed predominantly σ bonding which is similar to other reported transition metal ions in ionic insulating crystals. Orbital reduction, though no doubt present, makes only an insignificant and undetectable contribution.

Thermal conductivity and thermoelectric power of heavily doped n-type silicon

Abstract: Experimental values are given of the thermal conductivity and thermoelectric power of n-type silicon doped with phosphorus, antimony or arsenic, containing 4*1019 to 6*1025 m-3 electrons at room temperature, covering the range 4-300 degrees K. A theoretical treatment, using the variational method, suggests that the ratio of phonon drag component of thermoelectric power to thermal conductivity should be independent of carrier concentration, if the latter is not too large. This is verified experimentally; the temperature variation of the ratio is in satisfactory agreement with theory, which also gives the correct order of magnitude for the absolute value.

Activation Energy of Holes in Zn‐Doped GaAs

Abstract: The Hall effect and resistivity have been measured as a function of temperature for lightly Zn‐doped GaAs of better quality than previously available. Analysis of the Hall coefficient data yields activation energies which change with doping level. These results, along with earlier results on more heavily doped samples, can be represented by EA=0.0308−2.34×10−8(NIA)1/3 eV. The Hall mobility as a function of temperature leads to μL=400(300/T)2.41 for the lattice mobility of p‐type GaAs.

Properties of ion implanted silicon, sulfur, and carbon in gallium arsenide

Abstract: Work is described in which chromium-doped semi-insulating gallium arsenide has been successfully doped n-type with ion implanted silicon and sulfur, and p-type with ion implanted carbon. A dilute chemical etch has been employed in conjunction with differential Hall effect measurements to obtain accurate profiles of carrier concentration and mobility vs. depth in conductive implanted layers. This method has so far been applied to silicon-and sulfur-implanted layers in both Cr-doped semi-insulating GaAs and high purity vapor grown GaAs. In the case of sulfur implants, a strong diffusion enhancement has been observed during the annealing, presumably due to fast-diffusing, implantation-produced damage. Peak doping levels so far obtained are about 8 × 1017 electrons/cm3 for silicon implants and 2 × 1017 electrons/cm3 for sulfur implants. Mobility recovery has been observed to be complete except in regions near the surface which are heavily damaged by the implantation.

Threshold Requirements and Carrier Interaction Effects in GaAs Platelet Lasers (77°K)

Abstract: The experimentally observed thresholds for laser operation of optically pumped GaAs platelets are presented. The measurements were performed on uniformly doped samples of p‐type, n‐type, and compensated crystal (doping range 1014/cm3≤n, p≤1020/cm3). The observed thresholds are considerably lower than previously measured or predicted and exhibit no essential dependence upon impurity concentration. The 16‐meV shift of laser photon energy from bandgap in lightly doped GaAs is ascribed, as before, to electron‐hole‐lattice (EHL) interactions. Based upon the results of platelet laser threshold data and photon energy data, a comparison is made of the relative strength of the various EHL interaction mechanisms. If Coulomb interaction and dielectric screening can be ignored, over a certain doping range a remarkable fit of the photon energy data is afforded by the electron‐electron interaction mechanism.

Concentration‐Dependent Diffusion of Boron and Phosphorus in Silicon

Abstract: A model of enhanced diffusion of boron and phosphorus in silicon is proposed, which includes the effects of plastic deformation and the degeneracy of highly doped silicon. Numerical solutions of the diffusion equation with concentration‐dependent diffusion constant are presented, and the average conductivities of typical `anomalously diffused' silicon layers are given as a function of surface concentrations. Also discussed are the effects of background doping levels and surface concentrations on the effective diffusion constant and its measured activation energy.

The prediction of tunnel diode voltage-current characteristics

Abstract: This paper presents a simplified method of predicting the shape and magnitude of tunnel diode voltage-current characteristics when the substrate material and doping concentrations are specified. The method consists of first describing the tunnel diode V-I characteristics by an algebraic equation, the variables of which are then expressed as functions of the impurity densities. Previous theory is used to express the current variables, however the peak voltage expression is obtained by using Fermi-Dirac statistics and aligning the maximum of the density of electronic states with that of hole states. This leads to a verification and extension of Kane's predictions relating the peak voltage to the doping degeneracies. A comparison of the theory with the actual measured characteristic yields excellent agreement.

Double injection in semiconductors heavily doped with deep two-level traps

Abstract: Double injection is discussed for semiconductors heavily doped with deep recombination centers which act both as acceptors and donors. The current-voltage characteristics are derived using a generalization of the method due to Lampert for long structures in which diffusion can be neglected. Thermal emission from the traps and trapped space-charge effects are included. The resulting j - V curve shows in order of increasing current the following general features: an Ohmic regime, a low injection square law related to thermal emission, a negative resistance regime, a high injection square law, and finally a space-charge-limited cube law. A complete computer solution for the case of gold-doped silicon is given. Simple power laws for the various regimes, derived using the quasineutrality approximation, are found to agree well with the numerical solution. An expression is obtained for the voltage at the threshold of the negative resistance, and the effects of field dependent mobility are discussed quantitatively. Experimental results are presented for long (∼100 μm) gold-doped (∼10 16 cm −3 ) silicon p - i - n structures. The devices are fabricated from high purity n -type silicon, and large area alloy junctions are used. Pulsed I – V measurements at room temperature show an Ohmic regime, a square-law regime, and a negative resistance regime. These data are found to agree quantitatively with the theoretical calculations up to and including the onset of the negative resistance. In particular a strong temperature dependence is observed in the low injection square-law regime, which is different from that found in the Ohmic regime. This difference is explained in terms of the level structure of the gold impurity. The current for voltages above the onset of the negative resistance is approximately two orders of magnitude below the theoretical predictions. This indicates that filamentary conduction is probably occurring.

Anneal behavior of defects in ion-implanted GaAs diodes

Abstract: Doping of semiconductors by implantation of high-energy ions creates lattice damage which in general must be removed by annealing to form good qualityp-n junctions. Implantation of zinc or cadmium ions inton-type gallium arsenide substrates held at 400°C produces ap-n junction after the samples are annealed at elevated temperature (≥500°C for zinc, ≥600°C for cadmium). However, the resulting junctions are not abrupt; they contain a semiinsulating (I) layer and have ap-i-n structure. The thickness of the semiinsulating layer changes with annealing. For example, an implant of 1.3×1015 per sq cm, 20 kv, Zn+ ions produced a junction with an I layer of 28 μ thickness after annealing for 10 min at 600°C. An identically implanted sample, annealed for 10 min at 900°C, had an I layer thickness of 120 μ. A similar increase in I layer thickness with annealing was observed for samples implanted with 20 kv Cd+ ions at 400°C. Implantation of Zn+ and Cd+ ions into GaAs substrates held at room temperature produced junctions with much thinner I layers after annealing than those observed for the 400°C implants. The formation of the semiinsulating layer in the junction and its subsequent variation of thickness with annealing are attributed to deep diffusion of defects during the implantation or subsequent anneal, which produces compensation to the depth where the concentration of defects equals the substrate impurity concentration. The compensating centers are thought to be arsenic vacancy-substrate dopant atom complexes.

LASER EMISSION FROM METAL-SEMICONDUCTOR BARRIERS ON PbTe AND Pb(0.8)Sn(0.2)Te,

Abstract: Laser emission is obtained from forward biased evaporated metal barriers on degenerate p‐PbTe and p‐Pb0.8Sn0.2Te at T=4.2°K. Metals with small work functions such as In, Pb, and Zn produce a degenerate inverted n‐type surface region on p‐type samples without chemical doping. Low‐threshold laser emission has been obtained from these barriers on p‐PbTe at λ = 6.4μ and from Pb barriers on p‐Pb0.8Sn0.2Te at λ = 15μ.

Effect of carrier lifetime on the forward characteristics of high-power devices

Abstract: The influence of carrier lifetime on the characteristics of high-power devices has been examined from the standpoint of forward voltage drop at a given current, using existing theories of the p+ln+diode and allowing for carrier-carrier scattering effects. It is found that in the absence of recombination current in the heavily doped end regions, there exists an optimum base lifetime giving a minimum forward voltage. This minimum occurs because for increasing lifetime, the increase in junction voltage due to carrier buildup at the junction edge eventually overtakes the reduction in base voltage due to conductivity modulation. On the other hand, when the recombination currents in the end regions predominate over that in the base, their presence tends to inhibit carrier buildup, with the result that for sufficiently large values of base lifetime, the forward voltage falls to a limiting value. In certain cases, this value is less than the minimum voltage found in the absence of recombination in the end regions. In all the cases examined, the conclusion is that little is to be gained by further increase in lifetime beyond a certain value which depends on both the properties of the base and those of the end regions.

Electrical properties of silicon doped with platinum

Abstract: Results are presented and discussed concerning the effects of platinum in silicon. Platinum was diffused into N type and P type silicon at 900, 1100 and 1250°C for a time sufficiently long to obtain a constant concentration of platinum. When the platinum concentration is great enough N type silicon becomes distinctly P type. Measurements of resistivity vs. temperature show that platinum produces three levels in the forbidden band, one at 0·25 eV below the bottom of the conduction band and two at 0·30 eV and 0·36 eV above the valence band edge. It is shown that two of these levels are acceptor and it is assumed that the 0·25 eV level is double acceptor, the 0·36 eV level is single acceptor and the 0·30 eV level is donors. This model is discussed and it is verified by computations. These computations agree well with resistivity measured at room-temperature.

Deep levels within the forbidden gap of silicon-on-sapphire films

Abstract: The resistivity of silicon-on-sapphire films doped with a constant majority carrier concentration increases as the film thickness decreases. Analysis of data taken on both P -type and N -type films indicates that the Fermi level is being pinned by deep levels within the forbidden gap. These levels appear to be a donor level located about 0.3 eV from the valence band-edge and an acceptor level located about 0.25 eV from the conduction band. The levels are not sharp and have over 0.1 eV spread in energy. The presence of these levels has been corroborated by optical absorption and photoconductivity measurements. The donor-acceptor pair appear to occur in approximately equal densities, with densities as high as 10 17 –10 18 /cm 3 being deduced. The presence of these levels is tentatively associated with crystalline defects in the films and the possibility of precipitates occurring on these defects is considered.

Thermal and Sample-Size Effects on the Fluorescence Lifetime and Energy Transfer in Tetracene-Doped Anthracene

Abstract: The fluorescence decay time of anthracene crystals was studied for crystals of various sizes at numerous temperatures between 4.2 and 300 \ifmmode^\circ\else\textdegree\fi{}K. The decrease in the lifetime observed between 300 and \ensuremath{\sim} 140 \ifmmode^\circ\else\textdegree\fi{}K is attributed to changes in the amount of reabsorption, while the decrease observed between \ensuremath{\sim} 75 and 25 \ifmmode^\circ\else\textdegree\fi{}K is consistent with fluorescence emission from two types of levels with different intrinsic lifetimes whose populations are in thermal equilibrium. The time evolution of the anthracene and tetracene fluorescence intensities was also investigated for samples of various sizes and at numerous temperatures. The results cannot be explained by exciton diffusion theory and are consistent with the predictions of long-range-interaction theory only if an anomalously large value is assumed for the strength of the interaction. This discrepancy is not yet understood, but it is shown that it is not due to the effects of reabsorption.

Semiconductor doping compositions

Abstract: The disclosure herein relates to semiconductor doping compositions and to methods for their preparation and use. More particularly, the disclosure relates to liquid silica-based doping compositions which may be applied to a surface of a semiconductor substrate and, upon heating, an impurity is diffused from a film of the doping composition into the substrate to form a region therein having the desired electrical properties.