Showing papers on "Doping published in 1969"

Optical Spectra of Cr3+ Impurity Ions in Ferroelectric LiNbO3 and LiTaO3

Abstract: The optical absorption, luminescence, and excitation spectra of LiNbO3 and LiTaO3 doped with chromium impurities are examined as a function of temperature. Several interesting differences between these spectra and those of other chromium‐doped oxides are noted. The most important differences are the large halfwidth of the Cr3+‐ion “R” lines (∼50 cm−1 at 4.2°K) and the absence of any “R”‐line luminescence down to 4.2°K. Instead, a broadband emission peaking at about 1 μ is observed. It is shown that these differences arise from the low value of the crystal‐field parameter Dq at the Cr3+‐ion site in LiNbO3 and LiTaO3, so that the zero‐phonon 4T2 state of the Cr3+ ion lies at a lower energy than the 2E state. Point‐charge calculations of Dq for several oxides, including LiNbO3 and LiTaO3, and other considerations suggest that the most probable sites of the Cr3+‐ion impurities are the Nb/Ta sites and not the Li sites.

A technique for directly plotting the inverse doping profile of semiconductor wafers

Abstract: A new technique for plotting doping profiles of semiconductor wafers is described. This technique involves driving a Schottky diode deposited on the surface with a small constant RF current (a few hundred microamperes at 5 MHz). The depth of the depletion layer is varied by changing the dc bias, but this is the only role of the dc voltage. The inverse doping profile n-1(x) is obtained by monitoring the voltage across the diode at the fundamental frequency, which is proportional to the depth x, and the second harmonic voltage, which is proportional to n-1. This type of plotter has the advantages of simplicity, high resolution (limited only by the Debye length in most cases), immediate results, and economy.

Arsenic Isoconcentration Diffusion Studies in Silicon

Abstract: Arsenic radiotracer diffusions have been performed both in intrinsic and in homogeneously doped extrinsic silicon single crystals. Under intrinsic conditions, the tracer diffusion coefficient may be represented by the expression Di=60 exp (−4.20 eV/kT) cm2/sec. Measured in extrinsic silicon, in the absence of a concentration gradient, the tracer diffusion coefficient conforms with the relationship D=Di(n/ni), in which (n/ni) in the ratio of the free electron concentration in the extrinsic sample to that of intrinsic silicon at the diffusion temperature.

Magnetic Freeze-Out of Electrons in Extrinsic Semiconductors

Abstract: The density of states was derived and the statistics of conduction electrons were studied for the case of a strongly doped compensated semiconductor in an external magnetic field. The tail of the density of states and the spread in the energy distribution of impurity levels were investigated, and the temperature and magnetic field dependences of the concentration of electrons not localized in impurities were calculated. It is shown that, because of the tail of the density of states, this concentration approaches a finite limit when $T\ensuremath{\rightarrow}0$. The freeze-out of carriers begins when the magnetic field attains such a value that the binding energy becomes larger than the rms potential energy of an electron in the field of the impurities. For sufficiently large magnetic fields, the Fermi level will drop into the tail, although the electrons may remain degenerate. This last conclusion will also be true for uncompensated semiconductors.

Surface State and Interface Effects on the Capacitance‐Voltage Relationship in Schottky Barriers

Abstract: In the presence of an interfacial layer and semiconductor surface states, a Schottky barrier height φb decreases with increasing electric field E at the surface of the semiconductor. If the semiconductor doping concentration Nd is uniform throughout the depletion region and if [ (qNd/e) (dφb/dE)−E] [ (d2φb/dE2) (dE/dV) ]≪1, where V is the applied voltage and e is the semiconductor permittivity, the slope of the (capacitance)−2 vs voltage relationship is constant and can be interpreted to give Nd. The voltage intercept of the relationship yields an apparent barrier height φa related to the true barrier φb by φa=φb−E (dφb/dE) + (qNd/2e) (dφb/dE)2, where q is the electron charge. From the measured variation of φa with Nd and one absolute measure of φb at one value of Nd, φb(E), and dφb(E)/dE may be deduced. From dφb(E)/dE the surface state density as a function of energy in the bandgap and the minimum value of interface thickness divided by relative interface permittivity can be obtained. Using the data of Archer and Atalla for vacuum cleaved Au‐Si diodes to illustrate our method, the surface state density is found to peak at a value of ∼2×1014 cm−2·eV−1 at about 0.83 below the conduction band and the minimum value of interface thickness divided by relative dielectric constant is found to be of the order of 5 A. Criteria are given which show how Schottky diode capacitance‐voltage data may be further used, in conjunction with photoelectric barrier measurements, to detect the presence of deep lying impurities or the penetration of surface state charge into the body of the semiconductor.

Radiation-Induced Perturbations of the Electrical Properties of the Silicon-Silicon Dioxide Interface

Abstract: Interface-state densities and MOS transistor characteristics dependent upon such states have been studied as a function of radiation dose and type. Special MOS devices possessing doped silicon-dioxide layers as well as undoped "control" devices have been utilized. Infrared absorption measurements were performed on silicon-dioxide samples before and after exposure to radiation, as well as for doped and undoped samples. A model based on structural modifications of the silicon-dioxide-films is proposed for the build-up of interface-states resulting from exposure to radiation. It has been found that with the proper doping of the silicon-dioxide films, the build-up of such states can be reduced. Using such doped gate-dielectrics, planar semiconductor devices much less sensitive to radiation have been fabricated.

Minority carrier injection of metal-silicon contacts

Abstract: The minority carrier injection ratio from metal-silicon contacts has been measured using a metal-emitter transistor structure. Contacts of four different metals with barrier heights ranging from 0.65 to 0.85 eV on n -type silicon with doping level from 10 14 to 6 × 10 16 cm −3 were examined. This systematic investigation shows that the injection ratio at low current levels is a constant and is determined only by the barrier height of the contact and the doping of the semiconductor, while at high currents it increases with the total current. This result is in good agreement with theoretical predictions.

Deposited silicon diffusion sources

Abstract: Non-single crystal semiconductor material formed on a semiconductor substrate and separated from all but a portion of the substrate by an intervening insulation layer contains at least one dopant and preferably two dopants of opposite conductivity type. Heating the substrate, together with the overlying insulation and non-single crystal semiconductor layers, drives the dopants contained in the non-single crystal semiconductor material into the underlying semiconductor substrate in such a manner as to form diodes or transistors.

Electron shielding in heavily doped semiconductors.

Abstract: Electron shielding in heavily doped many valley semiconductors, discussing Thomas-Fermi screening and Mott transition

The realization of a GaAs—Ge wide band gap emitter transistor

Abstract: The fabrication and properties of an n-GaAs emitter, p-Ge base, n-Ge collector transistor which possesses significant current gain is described, These GaAs wide band gap emitter transistors have shown incremental current gains near 15 when operated at current densities up to 3500 A/cm2. The doping level used in the base region was quite high (up to 5×1019/cm3in order to avoid a spurious Ge p-n junction in this region. The epitaxial deposition of the GaAs emitter region was carried out at a low temperature in order to also avoid a hidden p-n Ge junction. The low deposition temperature resulted in low (about 5×1015/cm3emitter doping levels. The general nature of the GaAs-Ge heterojunction energy-band diagram permits this high doping in the base or Ge region relative to the GaAs emitter region without reducing the current gain below unity. The observation of gain in this n-p-n heterojunction structure where the emitter is much more lightly doped than the base is considered to be confirmation of the theoretical proposals of Shockley and Kroemer.

Optical Properties of n‐Type GaAs. III. Relative Band‐Edge Recombination Efficiency of Si‐ and Te‐Doped Crystals before and after Heat Treatment

Abstract: A study of the effect of annealing upon the efficiency of edge emission in heavily Si‐doped GaAs crystals reveals a substantially different behavior from that observed in Te‐doped GaAs crystals of comparable doping level. Essentially no change in the edge emission intensity at 77°K and a decrease of only a factor of two at 300°K is found for GaAs:Si after annealing in contrast to a decrease of a factor of 10 at 77°K and a factor of five at 300°K for GaAs:Te. The intensity of the 1.2‐eV band in GaAs:Si decreases after annealing while the same band increases in intensity in GaAs:Te. From the hole diffusion length and hole lifetime analysis, it is concluded that annealing GaAs:Si reduces SiVGa (Si‐donor‐Ga‐vacancy complex) centers but at the same time creates other unknown defects, both of which have smaller concentrations than some other compensating acceptors. These compensating acceptors are shown to be present only in GaAs:Si and are presumably Si acceptors. It is also demonstrated that the hole capture rates at SiVGa acceptors, at defects created during annealing, and at the compensating acceptors are all competitive in GaAs:Si after annealing, but only the hole capture rate at TeVGa is important in GaAs:Te. Although the 77°K hole lifetime is smaller for unannealed GaAs:Si than for GaAs:Te, the 77°K edge emission efficiency is approximately the same for both dopants if the crystals have the same room temperature carrier concentration. This result is due to the less steep absorption edge of Si‐doped crystals and the shift of the absorption edge to the lower energy. Similar behavior is also found for the 300°K case and is mainly due to the less steep absorption edge of GaAs:Si.

Transferred Electron Devices

Abstract: A transferred electron device includes a novel cathode giving improvement in the dc to microwave conversion efficiency over a wide temperature range. The cathode comprises a narrow n+ semiconductor zone next to the device active region or layer and, next to the n+ zone, a high field contact which includes a region of semiconductor.

The silicon-silicon dioxide system

Abstract: Study of the silicon-silicon dioxide system as a junction between a nearly ideal semiconductor and insulator has aroused both scientific and technological interest. Surface phenomena associated with this system are influenced by contamination and imperfections in the oxide, impurity redistribution in the silicon near the oxide, and finally by additional electronic energy states at the oxide-silicon interface. Over the past few years, the MOS (metal-oxide-semiconductor) approach has been highly developed and is the principal tool for the investigation of silicon surface phenomena. The theory of the ideal MOS capacitor is reviewed followed by a study of its use in the analysis of surface effects. Finally, the three-way relationship of the effect of oxide formation conditions and heat treatment on the properties of the oxidized silicon surface, and the subsequent influence of the properties of this surface on semiconductor device parameters is reviewed.

Si- and Ge-Doped GaAs p-n Junctions

Abstract: Si- and Ge-doped GaAs layers were obtained by a solution regrowth technique. They were p-type and their electric parameters ρ, µH, and p were found depending on the Si or Ge quantities in the melts. Ge-doped crystals had much larger µH values than Si-doped crystals. Si-doped p-n junctions showed I-V characteristics including tunneling and thermal components, while those of Ge-doped junctions had only a thermal component. Si-doped diodes showed photo responses originating from deep acceptor levels, while the photoresponses of Ge-doped ones were derived from a very shallow acceptor level. The same effects were seen in the emission spectra of these diodes. In the Si-doped ones, broad emission peaks were found at the longer wavelengths on account of the deep levels, while the emission spectra of Ge-doped diodes were sharp and concerned with the shallow acceptor level. An emission quantum efficiency of up to 2% was achieved in the Si-doped diode.

Optical and Electrical Properties of Uncolored and Colored Lead Doped Alkali Halides

Abstract: The peak position and half-widths of bands characteristic of lead impurity in four alkali halides, NaCl, KCl, KBr and KI, are reported. Ionic conductivity studies have been made in the temperature range 150–600°C in the four alkali halides doped with Pb. The values of the energy of association of Pb ++ with a cation vacancy is ∼0.28 eV. The growth rate of F-centers in X-irradiated crystals is found to be slower in all lead doped crystals. On additive or electrolytic coloration the lead band (characterised as the A band) disappears and an intense broad (half-width 2.5 eV) ultraviolet band, besides the F band, is observed. Quenching from temperatures greater than 500°C bleaches the F band and the UV band and a new band peaking at 240–265 nm with half-width 1.4∼1.5 eV is observed in four alkali halides. Preliminary EPR measurements did not show any influence of the lead bands on the EPR results.

Semiconductor bulk oscillator

Abstract: The semiconductor bulk oscillator includes a body of semiconductor material which includes a superlattice portion across which an electric field is applied. The device responds to this field to produce bulk high-frequency oscillations. The superlattice portion has a one-dimensional periodic spatial variation in its band edge energy produced either by doping or alloying. The periodic variation in band edge energy provides in wave vector space a plurality of minizones which are much smaller than the Brillouin zone. A cavity-type structure is formed transverse to the superlattice portion of the device to extract outputs of electromagnetic energy at high frequencies obtained when an electric field above threshold is applied across the superlattice.

Enhanced Gold Solubility Effect in Heavily n‐Type Silicon

Abstract: Using radiotracer methods, a study has been made of the increased gold solubility in uniformly heavily n‐doped silicon. Data for both phosphorus and arsenic showing gold solubility as a function of doping is presented. The gold solubility at 1000°C begins to increase substantially for concentrations of donor impurity in the range 1019 cm−3, although a difference in this increase between arsenic doping and phosphorus doping was noted. The data was related quantitatively to an ion pairing model which appeared to best explain the results.

Electron Mobility and Impurity Concentration in n -GaP Crystals Grown by Slow Cooling of Ga Solution

Abstract: n-GaP crystals were grown by slow cooling of Ga solution doped with various concentrations of Te. Electron mobility and carrier concentration in the crystals were measured in the temperature range from 77°K to 400°K. The analysis of mobility showed that the dominant process limiting the electron mobility is the intervalley scattering at 200–400°K and the scattering by space charge regions at 77–200°K. As for the intervalley scattering, the LA phonon near the X point, Tc=300°K, appeared to make a dominant contribution. The coupling constant for this phonon was estimated to be 0.7×109 eV/cm, just the same as the effective coupling constant for the dominant intervalley phonon in Si. The inhomogeneity in the crystals and the dependence of carrier concentration on doping level were also investigated and compared with those in the crystals grown by thermal gradient method and by vapor-phase epitaxy.

The Distribution of Condensed Defect Structures Formed in Annealed Boron-Implanted Silicon

Abstract: Silicon has been implanted with between 1014 and 1016 boron ions/cm2 at energies of 25, 50, 75 and 100 keV; it has also been annealed at temperatures of between 873 and 1073 °K when the implanted boron ions occupy substitutional sites and form a ‘doped’ surface layer in which the doping profile can be accurately controlled, a desirable property in the manufacture of solid state circuits and devices (Large & Bicknell 1967). The implanted layers have been examined by both electron microscopy and electron diffraction before, during and after annealing to study the changes in crystal structures involved. For transmission electron microscope studies the silicon must be thinned to provide areas less than 1 p m in thickness, otherwise the electron beam is entirely absorbed within the specimen. It has been found that a modified form of jet etching using a turbulent jet enables large areas suitable for transmission electron microscopy to be easily produced from all types of specimens, both annealed and unannealed. Although specimens have been prepared and implanted with boron ions of different energies and doses the results discussed, which are typical of the range covered, are those obtained from silicon implanted with single energy 50 keV boron ions with a dose of 2 x 1015 ions/cm2.

Low-temperature epitaxial growth of doped silicon films and junctions

Abstract: Studies of the structural and electrical properties of homo-epitaxial silicon films and junctions deposited at low temperatures by ultra-high vacuum sublimation have been made. Spreading resistance measurements of epitaxial layers sublimed from boron- and phosphorus-doped silicon sources have shown that films of known and uniform impurity concentrations could be deposited. Fault-free epitaxial layers have been grown on (111) at temperatures above 650°C, and on (100) at temperatures down to 500°C. Excellent silicon junction structures have been achieved at temperatures far lower than heretofore reported as demonstrated by junctions comprising 0.05 Ω-cm, P -type silicon epitaxial layers on 1.5 Ω-cm N -type, (100) substrates. These junctions, which in general show abrupt impurity profiles, are characterized by low reverse leakage currents and sharp voltage breakdowns close to the theoretical breakdown voltage anticipated from measured resistivity data. Minority carrier lifetimes ranging from 4 to 8 μsec have been measured by the carrier decay technique. The detrimental effects of substrate out-diffusion (resulting from the elevated temperatures used for cleaning the substrate surface prior to deposition) can be avoided by the sequential deposition of all-epitaxial junction structures. P + N − on N epitaxial structures with good junction properties have successfully been formed from highly P - and lightly N -doped sources.

Vapor Phase Growth of Stannic Oxide Single Crystals

Abstract: Single crystals of stannic oxide, , of higher purity and with higher Hall mobility than any previously reported have been grown from the vapor using the reaction at 1250° C and 10 Torr. The stannic chloride is obtained from the reaction which is performed in an external reactor and electrical doping is achieved by adding the desired dopant materials to tin charges in parallel doping reactors. The growth rate of the is controlled by adding additional Cl2 to the flow before it is introduced into the furnace; with sufficient Cl2 the crystals can also be etched. Important to the furnace design is a gas injection nozzle which eliminates growth immediately where the gases enter the furnace. Undoped crystals of resistivity at 300°K, and antimony‐doped n‐type crystals with resistivity, carrier concentration, and mobility of 0.1 ohm‐cm, , and 160 cm2/V‐sec at 300°K and of 0.1 ohm‐cm, , and 1200 cm2/V‐sec at 77°K have been grown, as have n‐i junctions.