Showing papers on "Doping published in 1971"

Hall Mobility in Chemically Deposited Polycrystalline Silicon

Abstract: Hall‐mobility measurements have been performed on polycrystalline silicon films deposited on a silicon oxide surface by the thermal decomposition of silane. Samples with doping impurities added during deposition or by diffusion from a doped vapor‐deposited oxide showed similar behavior. For both n‐type and p‐type samples approximately 5 μ thick, the mobility reached a maximum value of about 40 cm2/V sec at a free carrier concentration of about 1018 cm−3 and decreased for both higher and lower carrier concentrations. The observed Hall mobility was generally higher in p‐type samples than in n‐type samples. The decrease in observed mobility with decreasing carrier concentration is attributed to the effects of high resistivity space‐charge regions surrounding grain boundaries in the polycrystalline material. The mobility was seen to increase as the film thickness increased for samples with similar doping, indicating a more ordered structure in thicker films.

Current transport in metal-semiconductor-metal (MSM) structures

Abstract: The current-voltage characteristics of a metal-semiconductor-metal structure (essentially two metal-semiconductor contacts connected back to back) have been studied based on the thermionic emission theory. When a uniformly doped semiconductor is thin enough that it can be completely depleted before avalanche breakdown occurs, the structure can exhibit many novel transport behaviors. Two outstanding features of the structure are that (1) a wide range of high-level injection of minority carriers can be achieved by varying the barrier heights of the two contacts and (2) the critical voltage at which the minority carrier injection increases rapidly can be varied by varying the semiconductor doping and thickness. Experimental silicon MSM structures of PtSi-Si-PtSi have been made from n-type silicon with doping of 4×1014 cm−3 and thickness of 12 μm. The critical voltage at room temperature is about 30 V. The current increases over five orders of magnitude with only 10 per cent increase of the voltage. The above results and other measurements over wide temperature range do substantiate the theoretical predictions.

Holographic pattern fixing in electro‐optic crystals

Abstract: This paper describes the results of an investigation into techniques for obtaining erasure resistant holograms in electro‐optic crystals. The most successful approach made use of thermally activated ionic drift during or after recording. The samples are heated for about 30 min at 100°C to obtain optically nonerasable holograms with as much as 50% diffraction efficiency in LiNbO3 or in doped Ba2NaNb5O15.

Specific contact resistance of metal-semiconductor barriers

Abstract: The specific contact resistance at zero bias, R c , serves as a measure of the ohmic or rectifying behavior of a metal-semiconductor barrier under operating conditions. It is thus an important design parameter for semiconductor devices. The values of R c have been calculated for Metal-Si and metal-GaAs barriers on p -type and n -type samples. The theoretical calculation is based on the generalized transport study of metal-semiconductor systems. The results, which are presented graphically, show the dependence of R c on temperature over the range 50°K–500°K, the barrier height from 0.2 to 1.0 eV, and the ionized impurity concentration from 10 14 to 10 21 cm −3 . Generally R c decreases exponentially with increasing temperature and with decreasing barrier height. For samples with lower dopings where the thermionic emission dominates, R c is essentially independent of doping; for higher dopings where the tunneling dominates, R c decreases rapidly with increasing doping. The experimental results of R c for various metals on silicon samples are in good agreement with the predictions.

Film Deposition by Molecular-Beam Techniques

Abstract: A review of molecular-beam epitaxy of GaAs and the observation of surface structures with high-energy electron diffraction in an ultrahigh-vacuum system is described. The utilization of these surface structures as growth conditions to produce n- and p-type layers when doped with Sn, Ge, and Mg, and the electrical and optical evaluations of the layers thus grown is also discussed. The molecular-beam epitaxy method may be used to fabricate extremely thin multilayer structures and may play an increasing role in semiconductor technology.

The influence of debye length on the C-V measurement of doping profiles

Abstract: The doping profile of a semiconductor is given only approximately by the conventional analysis of C-V measurements. The present study employs computer simulation of semiconductors with one-sided doping profiles that consist of high and low doped sections joined by steps and linear ramps. The computation yields the apparent doping profile that would be obtained by the conventional use of C-V data, and this result is compared with the actual profile, with the majority-carrier distribution, and with the outcome of a correction previously proposed in the literature. The results show that a step in the profile cannot be resolved satisfactorily to less than several Debye lengths corresponding to the doping on the high side of the profile. A ramp cannot be distinguished accurately from a step unless its width is appreciably greater than a Debye length. Furthermore, the apparent doping profile is not identical with the majority-carrier distribution with contacts far away, as has been suggested, and the discrepancy is shown to depend on the side from which depletion is done.

Optical Studies of Shallow Acceptors in CdS and CdSe

Abstract: We show that Li and Na are the only soluble substitutional acceptors in CdS and CdSe with relatively small binding energies. A shallow acceptor is observed for P doping, but it arises from a complex. These results, and also the fact that the substitutional P is a deep acceptor in the sulfides and selenides, but not in the tellurides, are consistent with the trends in acceptor binding energy observed in other semiconductors. We present evidence that a native double donor exists in CdS, but that Li and Na acceptors are compensated by ordinary donors and not by isolated double donors. Analysis of thermodynamic data shows that isolated native donors should not be effective in compensating acceptors in ZnSe, CdSe, or CdTe. The compensating donors in CdS are found to be unusually shallow, indicating that they may be Li or Na interstitials. An attempt to drift out the Li-interstitial donors with an applied electric field is discussed.

Electronic Specific Heat of Metallic Ti-Doped V 2 O 3

Abstract: In the system (${({\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x})}_{2}{\mathrm{O}}_{3}$, the antiferromagnetic insulating phase is suppressed for $xg0.05$. The linear term in the heat capacity is very large ($\ensuremath{\gamma}=192\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ cal \ifmmode^\circ\else\textdegree\fi{}${\mathrm{K}}^{\ensuremath{-}2}$ per mole of ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$), and the magnetic susceptibility at 4.2\ifmmode^\circ\else\textdegree\fi{}K is 2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ emu ${\mathrm{mole}}^{\ensuremath{-}1}$ giving a value $\frac{\ensuremath{\chi}}{\ensuremath{\gamma}}=1.8$. The results are interpreted as evidence for a strongly correlated metallic phase.

Growth of High‐Purity and Doped Alkaline Earth Oxides: I. MgO and CaO

Abstract: A new variation of the carbon arc‐fusion technique is reported which makes possible the growth of large, high‐purity MgO and CaO single crystals which are free of microbubbles. A technique has also been developed for impurity doping. We have successfully doped MgO with Na, D, Ce, Eu, Gd, Dy, and Yb; and CaO with Li, Na, Ce, and Nd. The presence of these dopants has been ascertained by chemical analyses, optical, or EPR measurements. EPR signals showed minimal effects from strains in these crystals.

The Effect of Nitrogen Doping on GaAs1−xPx Electroluminescent Diodes

Abstract: The efficiency of GaAs1−xPx diodes for x>0.45 has been found to be greatly enhanced by the addition of nitrogen doping. The diodes were fabricated by means of Zn diffusion into vapor‐grown GaAs1−xPx doped with N and Te. The effects of nitrogen doping on diode efficiency, emission spectra, and brightness as a function of alloy composition are discussed.

P‐N Junction Formation during Molecular‐Beam Epitaxy of Ge‐Doped GaAs

Abstract: Germanium was used to dope both the n and p layers of GaAs grown when molecular beams containing Ge, Ga, and As2 simultaneously impinged on the substrate surface. The formation of n‐ or p‐type layers is dependent on the ratio of As2/Ga in the molecular beam and the substrate temperature. We describe the process used for the doping as well as the photoluminescence spectra from these layers.

Threshold voltage variations with temperature in MOS transistors

Abstract: Variations with temperature in the threshold voltage of n- and p-channel MOS transistors are obtained by calculation as well as measurement, with the results comparing quite closely. The amount of voltage change per °C under normal operating conditions is found to be dependent upon the channel doping concentration. The calculations show that for either n- or p-channel devices the voltage change per °C is -4 mV/°C for an impurity concentration of 3 × 1016/cm3and -2 mV/°C for an impurity concentration of 1015/cm3. This information is important because if the MOS transistor is subjected to a changing temperature environment, the accompanying threshold voltage change may be intolerable.

Dependence on Crystalline Face of the Band Bending in Cs2 O‐Activated GaAs

Abstract: Electron energy loss in the band‐bending region of the p‐type III–V semiconductor in a III–V photocathode is an important factor in determining the escape probability and the optimum doping. From measurements of photoelectric yield near threshold from Cs2O‐activated n‐type GaAs, the position of the Fermi level at the GaAs–Cs2O interface was determined for {110}, {100}, {111A}, and {111B} surfaces. Assuming the Fermi‐level position at the GaAs surface to be independent of doping, the band bending for p‐type GaAs is greatest for the {111A} face and least for the {111B} face. The measured escape probabilities of photoexcited electrons from different crystalline faces of optimally activated 5 × 1018/cm3 Zn‐doped liquid epitaxial GaAs correlate well with the band‐bending measurements. The {111B} sample has an escape probability of 0.489 and a luminous sensitivity of 1837 μA/lm.

Electrochemical Cells and Electrical Conduction of Pure and Doped Al2O3

Abstract: Data concerning the types of charge carrier responsible for electrical conduction in single-crystal aluminum oxide are reviewed, and explanations are offered for discrepancies in terms of the experimental conditions. Measurements on undoped and Co2+ and Mg2+ doped crystals, made using a volume guard to avoid surface and gas conduction, are used to describe Al2O3 as an ionic conductor with Al interstitial ions as the principal charge carriers at high oxygen activity. A defect model is proposed and the mobility of Ali3+, the concentration of Ali3+ in undoped crystals, and the equilibrium constant for defect formation at high temperatures are estimated.

Bistable resistance device which does not require forming

Abstract: A switchable device using a doped insulator having two stable resistance states which does not require application of a forming voltage when being fabricated. The insulator is, for example, a multivalent oxide of 100-2,500 A thickness, containing impurities which provide conduction centers. Examples of these impurites include Bi, Sb, As, P, Ti, W, in amounts 0.05-10 percent by weight (1018- 1021 impurities/cm.3). The insulator is contacted by two electrodes which can be metals, such as transition metals. A particularly good device is NbBi alloy - NbBixOy-Bi.

Bistable switching in organic thin films

Abstract: Field-induced switching between two impedance states has been observed in both pure and doped organic thin films. Aromatic hydrocarbon films display this phenomenon reproducibly when a mobile electrode material such as gallium-indium alloy is employed. Controlled doping of the hydrocarbons with electron acceptors leads to reproducible switching characteristics which are not electrode dependent. For the doped films, activation energies of conduction typical of bulk charge-transfer complexes characterize the low impedance states whereas the activation energies of the high impedance states are typical of organic insulating films. It is suggested that the switching mechanism involves the formation of conducting filaments.

Non-equilibrium effects on metal-oxide-semiconductor tunnel currents☆

Abstract: A d.c. tunnel current saturation under negative bias is observed for N -type MOS devices when average oxide thicknesses of d 0 A and non-degenerate (10Ω cm) semiconductors are employed. A model is proposed that allows the voltage distribution across devices in such a non-equilibrium situation to be calculated. Theoretical tunnel current expressions are derived and a comparison with experimental results made. The dependence of the existence of this saturation on semiconductor doping concentration, oxide thickness, and minority carrier injection is investigated. Consideration of band tunnel currents, and the effects of surface state charge, oxide charge, and work function differences on these currents, is shown to be sufficient to explain much of the observed current-voltage characteristic.

Epitaxy of Silicon Doped Gallium Arsenide by Molecular Beam Method

Abstract: The molecular beam method is a versatile experimental technique which may be used to grow high quality single crystal thin films in the range from 100A to several microns with precise control of uniformity and thickness. Films may be doped by an additional molecular beam containing the doping material simultaneously impinging on the substrate surface with the film molecular beams. Epitaxial GaAs thin films doped with silicon were grown by the molecular beam method in an ultrahigh vacuum system in which high energy electron diffraction and mass spectrometric measurements could be made during growth or by stopping growth momentarily. The crystallinity and beam intensity parameters of these films were thus studied during growth. The doping profiles and the amount of compensation were evaluated by the Schottky barrier diode method and the photo luminescence spectra.

Method of making semiconductor devices with selective doping and selective oxidation

Abstract: A method of manufacturing a semiconductor device having an inset oxide pattern obtained by local oxidation, which pattern is bounded only partly by a doped surface zone. According to the invention a first mask is provided on the semiconductor surface after which etching is carried out so that a freely projecting edge of said mask is formed by underetching. During the local doping of the etched surface the masking provided by said edge is used directly or indirectly after which the oxide pattern is provided.

ESR of Exchange Coupled Cr3+ Ions in Phosphate Glass

Abstract: A study of the ESR spectrum of a phosphate glass heavily doped with Cr2O3 is reported. The spectrum is attributed to exchange coupled Cr3+ ion pairs and is interpreted with reference to a spin Hamiltonian containing isotropic exchange, Zeeman, and fine structure terms. From the temperature dependence of the ESR intensity, it is inferred that the coupling is antiferromagnetic with an average coupling constant J=24±2 cm−1. The effects of fine structure interactions on the lineshape and breadth of the glass spectrum are considered, and the magnitudes of the fine structure parameters are estimated from the observed linewidths and dependence of the lineshape on microwave frequency. It is found that the fine structure constants are distributed in the range from 0.03 to 0.3 cm−1. The majority of the pairs are characterized by values near the lower end of the range, but the higher values are required to account for the absorption in the wings of the line.

Dopant Diffusion in Silicon. III. Acceptors

Abstract: Aluminum, gallium, indium, and thallium acceptors have been diffused into (111) silicon from doped epitaxially deposited source layers in a flowing hydrogen atmosphere. As in the case of P, As, Sb, and Bi donors reported earlier, all these acceptors show significantly lower mobilities when freed from surface effects. The temperature dependence of the intrinsic diffusion coefficients, obtained above 1120 \ifmmode^\circ\else\textdegree\fi{}C, are characterized by the following preexponential and activation-energy parameters: 1.385, 0.374, 0.785, (1.37) ${\mathrm{cm}}^{2}$/sec, and 3.41, 3.39, 3.63, (3.70) eV/atom for Al, Ga, In, Tl, respectively. An analysis of these diffusion characteristics indicate a similar point-defect mechanism for both group-III and group-V dopants in silicon.

Connection means for semiconductor components and integrated circuits

Abstract: In a semiconductor wafer having an epitaxial layer on which circuit elements are formed, through-connections for said circuit elements to contacts formed on the opposite surface of the layer are provided by tapered high conductivity semiconductor regions insulated from the body by a thin layer of dielectric material and in contact with suitably doped portions of the epitaxial layer to provide insulation by means of reversely biased junctions.

Localized vibrational modes of light impurities in gallium phosphide. (Absorption spectra)

Abstract: Vibrational absorption due to boron, carbon, nitrogen, silicon, aluminium and arsenic has been observed in gallium phosphide crystals. It is concluded that 11B and 10B give gap modes with a separation of about 1.5 cm-1. Previously reported absorption bands at 849 and 882 cm-1 have only been detected in electron irradiated zinc doped crystals, and it would appear that they cannot be due to local+gap combinations. It has been confirmed that a line at 496 cm-1 is due to 14N, and it has been shown unambiguously that another line at 465 cm-1 is due to silicon as a result of observed isotopic splittings. Mass spectrographic and electrical measurements made on some of the samples examined has allowed estimates to be made of the apparent charges associated with the various impurities.

Distribution Coefficient of Germanium in Gallium Arsenide Crystals Grown from Gallium Solutions

Abstract: Gallium arsenide crystals doped with germanium were grown from gallium solutions at 900°–875°C. The Ge concentration in the liquid was varied from 0.004 to 56 at.%, and the Ge concentration in the GaAs crystals determined using radiotracer and other techniques. The Ge concentration in the solid varied linearly with increasing Ge concentration in the liquid up to 5 at.% and kGe = (Ges)/(Gel)=0.0083±0.001. Above 5‐at.% Ge in the growth solution, kGe increased. At low doping levels Ge acts predominantly as a simple acceptor substituting on arsenic sites. At high doping levels, in the extrinsic range, the Ge concentration in the solid is considerably greater than the free carrier concentration. The form in which the excess Ge exists is not known.

Electroluminescence Characteristics and Efficiency of GaAs:Si Diodes

Abstract: The peak wavelength, spectral half‐width, and efficiency of liquid‐phase epitaxial GaAs:Si diodes were determined as a function of silicon concentration in the melt. The peak of the emission spectrum could be shifted from about 9200 to 10 000 A by varying the silicon concentration. For all wavelengths investigated, uncoated diodes with 6% efficiency could be made, with some going as high as 10%. External room‐temperature dc efficiencies up to 32% were measured on diodes provided with high‐index glass domes. The spectral half‐width was found to increase with silicon concentration, and was especially large for growth on the 111B plane. The internal absorption loss was found to be significant for all peak wavelengths. These findings are discussed in the light of current models of recombination processes in heavily doped semiconductors.

Transparent conducting films of antimony doped tin oxide on glass

Abstract: A simple laboratory technique for the routine preparation of transparent conducting films on soda and borosilicate glasses is described. The process uses the surface hydrolysis of stannic chloride at a temperature approaching the softening point of the glass. High electrical conductivity (50 Ω/sq) and good optical transmission (80%) have been obtained by the addition of small quantities of antimony and the optimization of deposition conditions. The technique has been found to give uniform and consistent results.

Measurement of Free‐Carrier Lifetimes in GaP by Photoinduced Modulation of Infrared Absorption

Abstract: A new technique is presented for measuring the lifetimes of both minority and majority photoexcited free carriers in GaP. The technique is useful for both n‐ and p‐ type material in any doping range and involves measurement of the modulation of the free‐carrier infrared absorption induced by photoexcited free carriers. In GaP(Zn, O) we find that the minority‐carrier (electron) lifetime ranges from 1 to 20 nsec, and the majority‐carrier (hole) lifetime ranges from 0.1 to 2 μ sec. A saturation effect is observed which is consistent with the view that the dominant recombination path in GaP(Zn, O) is through a deep acceptor via an Auger mechanism.