Showing papers on "Doping published in 1982"

Detailed photocurrent spectroscopy of the semiconducting group VIB transition metal dichalcogenides

Abstract: Summary of Band Gaps Measured for Various Compounds in This Studya The Journal of Physical Chemistty, Vol. 86, No. 4, 1982 467 sitions to a pseudo-two-dimensional system with d-d transitions. It is unclear whether the parabolic band as- sumption which is used in the three-dimensional materials is valid for these systems.lg The angle of incidence and the polarization of the in- cident light were varied in hopes that the change in the electric vector of the incoming radiation would couple the radiation more or less to the electronic transitions in the layered compound. Gerischer has observed an effect of the polarization and the angle of incidence on the photo- current spectxa of GazSePm The angular dependence was studied for p-polarized light with a normalization to s- polarized light at normal incidence for several doping levels in the semiconductor. The large angular dependences that were observed were explained by a large anisotropy in the absorption coefficient and by different diffusion lengths associated with the impurity doping. We were unable to measure significant changes in the photocurrent spectra as a function of the polarization

Electrical properties and defect model of tin-doped indium oxide layers

Abstract: Tin-doped In2O3 layers were prepared by the spray technique with doping concentrationsc Sn between 1 and 20 at. % and annealed at 500 °C in gas atmospheres of varying oxygen partial pressures. The room-temperature electrical properties were measured. Maximum carrier concentrationsN=1.5×1021cm−3 and minimum resistivities ϱ=1.3×10−4 Ω cm are obtained if the layers are doped withc Sn≈9 at. % and annealed in an atmosphere of oxygen partial pressurep O2 ⋦10−20 bar. At fixed doping concentration, the carrier mobility increases with decreasing oxygen pressure. The maximum obtainable mobility can be described in terms of electron scattering by ionized impurities. From an analysis of the carrier concentration and additional precision measurements of the lattice constants and film thicknesses, a defect model for In2O3:Sn is developed. This comprises two kinds of interstitial oxygen, one of which is loosely bound to tin, the other forming a strongly bound Sn2O4 complex. At low doping concentrationc Sn≲4 at. % the carrier concentration is governed by the loosely bound tin-oxygen defects which decompose if the oxygen partial pressure is low. The carrier concentration follows from a relationN=K 1 ·p O2 −1/8 ·(3 ×1010 × cSn −N)1/4 with an equilibrium constantK 1=1.4×1015 cm−9/4bar1/8, determined from our measurements.

Direct measurement of gap state absorption in hydrogenated amorphous silicon by photothermal deflection spectroscopy

Abstract: We have measured the subgap otpical absorption of undoped, singly doped, and compensated hydrogenated amorphous silicon down to 0.6 eV using the sensitive technique of photothermal deflection spectroscopy. We show that this absorption is due to silicon dangling-bond defects located approx.1.4 eV below the conduction band. While doping also creates defects approx.1.4 eV below the conduction band, compensation removes them. The results suggest that for the undoped material the density-of-states maximum found in field-effect measurements is due to silicon dangling bonds.

Doping and the Fermi Energy in Amorphous Silicon

Abstract: The doping of hydrogenated amorphous silicon is discussed within the context of Mott's $8\ensuremath{-}N$ rule, and found to have properties distinctly different from dopants in crystalline silicon. A unifying description of dopant and defect states based on the position of the Fermi energy is given. Some possible consequences of the $8\ensuremath{-}N$ rule for the deposition and structure of $a$-Si: H are also discussed.

Nonstoichiometry in Acceptor‐Doped BaTiO3

Abstract: The effect of added Al, as an acceptor impurity, on the equilibrium electrical conductivity of large-grained, polycrystalline BaTiO3, is consistent with a previously proposed defect model which involves only doubly ionized oxygen vacancies, electrons, holes, and acceptor impurities. The behavior is an extension of that of undoped BaTiO3, in which an accidental net acceptor excess already plays an important role. Comparison of the derived active acceptor content with the amount of added Al indicates that Al is <50% effective in creating acceptor levels. The magnitude of a small Po2-independent conductivity component, necessary to fit the observed conductivity minima, increases with added Al content. This is consistent with a contribution from extrinsic oxygen vacancy conduction.

Electrical and optical properties of tin oxide films doped with F and (Sb+F)

Abstract: This paper presents the structural, electrical, and optical properties of F‐ and (Sb+F)‐doped tin oxide films prepared by spray pyrolysis technique. Resistivity as low as 5.5×10−4 Ω cm with high optical transmission (≳80%) and high infrared reflection (∼90%) have been obtained in F‐doped tin oxide films. The figure of merit ΦTC = T10/Rsh (52.6×10−3Ω−1 at 0.65μm) of these films is the highest amongst the results reported on doped tin oxide films. The variation of mobility with doping concentration has been analyzed to understand the electron–conduction mechanism. The Drude theory has been used to explain the optical properties near the plasma edge.

Dielectric properties of donor-doped polycrystalline SrTiO3

Abstract: Various donor dopants such as Y3+ and Nb5+ were incorporated in SrTiO3 in amounts ⩽25 mol % during sintering in air at 1450° C for ⩽ 15 h Dense ceramic materials with grains of optimum uniformity and largest size were obtained when the cation stoichiometry was adjusted to allow for charge compensation of the donor ions by strontium vacancies For donor levels ≳ 03 mol%, the dielectric constant measured at 25° C and 1 kHz was up to two orders of magnitude higher than that of undoped strontium titanate The increase in permittivity, however, was dependent on grain size, was influenced by the method of electrode application, and was suppressed by the presence of ≲ 01 mol% Mn in the ceramic These observations, together with data obtained from electrical measurements at other temperatures and frequencies, were consistent with interpretation of the anomalously high dielectric constant as a boundary-layer effect resulting from semiconducting grains and weakly insulating grain-surfaces It is suggested that donor doping influences the electrical properties of SrTiO3 mainly by increasing the volatility of oxygen from the grains during sintering, and by decreasing the rate of re-oxidation during cooling

A physical model for the dependence of carrier lifetime on doping density in nondegenerate silicon

Abstract: A theoretical model that describes the dependence of carrier lifetime on doping density, which is based on the equilibrium solubility of a single defect in nondegenerately doped silicon, is developed. The model predictions are consistent with the longest measured hole and electron lifetimes reported for n -type and p -type silicon, and hence imply a possibly “fundamental” (unavoidable) defect in silicon. The defect is acceptor-type and is more soluble in n -type than in p -type silicon, which suggests a longer fundamental limit for electron lifetime than for hole lifetime at a given nondegenerate doping density. The prevalent, minimum density of the defect, which defines these limits, occurs at the processing temperature below which the defect is virtually immobile in the silicon lattice. The analysis reveals that this temperature is in the range 300–400°C, and thus emphasizes, when related also to common non-fundamental defects, the significance of low-temperature processing in the fabrication of silicon devices requiring long or well-controlled carrier lifetimes.

Modeling and measurement of minority-carrier lifetime versus doping in diffused layers of n + -p silicon diodes

Abstract: The results of minority-carrier lifetime measurements in heavily phosphorus-doped n+diffused layers of p-n junction diodes using a spectral response technique are reported in this paper. Exact modeling of current-flow equations, modified to include bandgap reduction due to high carrier concentration and Auger recombination, is used to compute the dependence of diffused-layer photocurrent J pth on the incident light energy and intensity. The photocurrent in the diffused layer is also obtained by subtracting the theoretical value of the space charge and uniformly doped p-region component from the experimentally measured photocurrent of the diode at each wavelength. Note that all calculated values based on light intensity include computed transmittance/reflectance through the oxide layer at each wavelength. The comparison of the values of J pth with J pexp , using nonlinear least square techniques, then directly gives the lifetime profile in the diffused layer. A simple expression is given for lifetime as a function of doping which may be used in modeling and prediction of device performance. Using this experimental technique it was found that the lifetime in the diffused layer is an order of magnitude less than that corresponding to uniformly doped bulk-silicon values and is very much process dependent; its value being 3.72 × 10-11s for surface concentration of 3.0 × 1020cm-3and increases to 2.9 × 10-8s at doping concentration of 1.0 × 1017cm-3.

Electrical properties and photoluminescence of Te‐doped GaAs grown by molecular beam epitaxy

Abstract: The application of PbTe as a molecular tellurium source in the growth of n‐type GaAs:Te by molecular beam epitaxy (MBE) has been investigated. We obtained free‐carrier concentrations ranging from 2×1016 to 2×1019 cm−3. In particular in degenerate n‐type material, excellent 77 K Hall mobilities were achieved. Even at high impurity concentrations (≳1018 cm−3), Te was not found to accumulate at the surface if a true Pb‐saturated (n‐type) starting material was used as dopant source. Using low‐temperature photoluminescence measurements, we further studied the influence of the doping concentration on the shift of the Fermi level and on the radiative recombination across the fundamental gap in heavily n‐doped GaAs:Te. Calculations based on the Burstein‐Moss shift and on the band tailing effect, as well as a line shape analysis, were performed for a distinct interpretation of the observed luminescence behavior. At concentrations below 5×1017 electrons cm−3, band‐acceptor transitions involving residual carbon acce...

Properties of hydrogenated amorphous carbon films and the effects of doping

Abstract: Amorphous carbon films have been prepared in a r.f. glow discharge from various hydrocarbon gases. Electrical conductivity and optical absorption measurements show a strong dependence on the preparation gas and on the substrate temperature T d. Particularly for specimens prepared from ethylene, varying T d from 230 to 300°C increased the conductivity by ten orders of magnitude and decreased the optical gap from 2·0 to 0·8 eV. The hydrogen content of the specimens, measured by the thermal evolution technique, lies between 30% and 45% and shows no systematic dependence on T d or the preparation gas. Results are also presented for films which have been prepared from gas mixtures containing small predetermined amounts of phosphine, diborane or nitrogen. The addition of each dopant gas increases the specimen conductivity by between one and three orders of magnitude, depending on T d. It is concluded that for both undoped and doped specimens, conduction is predominantly by hopping in a region of fairly...

Magnesium‐ and calcium‐doping behavior in molecular‐beam epitaxial III‐V compounds

Abstract: Residence lifetimes of Mg on GaAs surfaces were observed using 10 KV reflection electron diffraction and Auger electron spectroscopy to decrease from ∼120 s at 550 °C to ∼1 s at 600 °C. The electrical incorporation coefficient is ∼0.3 at and below 500 °C decreasing to ∼3×10−4 at 600 °C at the expense of desorption. Hole mobilities of uniformly Mg‐doped samples are as good as those for equivalently Be‐doped GaAs samples. Calcium does not behave as a shallow acceptor in GaAs grown by molecular‐beam epitaxy.

Precipitation as the phenomenon responsible for the electrically inactive phosphorus in silicon

Abstract: The physical nature of the electrically inactive phosphorus in silicon was investigated by annealing experiments performed on laser annealed specimens doped by ion implantation up to 5×1021 at/cm3. The hypothesis of point defects, which compensate or make the excess dopant electrically inactive, is contradicted by the experimental results. It was verified that phosphorus solubility corresponds to the electrically active concentration in equilibrium with the inactive dopant, and that the latter is precipitated phase. This was confirmed by transmission electron microscopy (TEM) examinations with the weak beam technique, which detected a high density of very small coherent precipitates. This method allowed us to observe particles of the same kind even on specimens thermally predeposited in conditions typical of device technology. In both cases the amount of precipitates was consistent with the inactive dopant concentration. In addition these experiments show that precipitation is associated with a high enhan...

Adsorbate effects on the electrical conductance of a-Si: H

Abstract: The influence of adsorbates such as water and ammonia on the electrical conductance of hydrogenated amorphous silicon, a-Si: H, has been studied as a function of doping, temperature, thickness, sur...

The Nature of the Passive Film on Iron III . The Chemi‐Conductor Model and Further Supporting Evidence

Abstract: A new model, which describes the behavior of the passive film on iron more adequately than the usual semiconductor model, is presented. We define a chemi‐conductor as an insulator whose stoichiometry can be varied by oxidative and/or reductive valency state changes. These nonstoichiometries can then modify the local electronic (and/ or ionic) conductivity of the film. This is equivalent to variable doping with defects rather than with a foreign species. The passive film is pictured as an insulating ferric oxyhydroxide with a principal (O 2p‐Fe 4s) gap at ∼5.5 eV. Small (<5%) nonstoichiometries, primarily Fe2+ near the inner (metal‐film) interface and Fe4+ near the outer (film‐solution) interface, affect the local conductivity in the film. These defects, probably associated with excess (or deficient) protons, are modulated by the externally applied potential, mimicking semiconductor behavior.

Electron mobilities in modulation doped Ga0.47In0.53As/Al0.48In0.52 As heterojunctions grown by molecular beam epitaxy

Abstract: Modulation doped Ga0.47In0.53As‐Al0.48In0.52 As single‐period heterostructures have been prepared by molecular beam epitaxy (MBE). Electron mobilities as high as 8915 cm2/V s at 300 K, 60 120 cm2/V s at 77 K, and 90 420 cm2/V s at 10 K were obtained with an average electron concentration of ∼1017 cm−3. These results represent a mobility enhancement over uniformly doped Ga0.47In0.53 As with the same carrier concentration by about a factor of 6 at 77 K and by a factor of 2 at 300 K. Single‐period modulation doped heterostructures have shown enhanced mobility in spite of the relative positions of the Si‐doped Al0.48In0.52 As layer and the undoped Ga0.47In0.53 As layer in contrast to the case of GaAs/AlxGa1−x As system where mobility enhancement has only been observed for MBE grown AlxGa1−x As on top of the undoped GaAs layer.

On the position of energy levels related to transition-metal impurities in III-V semiconductors

Abstract: Deep levels are often believed to be tied to one or other of the band edges in a semiconductor. There is, however, evidence that the deep level link is with the vacuum, and independent of the particular III-V semiconductor.

Method of making aluminum gate self-aligned FET by selective beam annealing through reflective and antireflective coatings

Abstract: A method for producing a semiconductor device comprising the steps of forming a gate insulating layer (3) on a semiconductor substrate having a first conductivity (1) and forming an aluminum gate electrode (4) on the gate insulating layer (3); impurity doped regions (5, 6) are then formed in the semiconductor substrate (1) by means of implantation of impurity ions having a second conductivity opposite that of the first conductivity into the semiconductor substrate (1) using the aluminum gate electrode (4) as a masking material for annealing the impurity doped regions (5, 6). The annealing process occurs by irradiating a beam on the impurity doped regions (5, 6) including the aluminum gate electrode (4). After forming the impurity doped regions (5, 6) in the semiconductor substrate (1), at least the upper surface of the aluminum gate electrode (4) is covered with an insulating layer (7).

Si and Sn Doping in AlxGa1-xAs Grown by MBE

Abstract: Electrical properties of Si and Sn doped AlxGa1-xAs epitaxial films grown by MBE have been studied in the wide range of AlAs mole fraction. With a constant doping level, decrease in the carrier concentration was observed around the direct-indirect band crossover point, for Si-doped and Sn-doped AlxGa1-xAs. Abrupt increase in donor ionization energy ED occurred in Si-doped AlxGa1-xAs films. These characteristics are similar to those reported for Te and Sn doped AlxGa1-xAs grown by LPE.

Ga-Doped ZnSe Grown by Molecular Beam Epitaxy for Blue Light Emitting Diodes

Abstract: The MBE-grown ZnSe layer on GaAs (100) with an optimum doping of Ga is found to exhibit an extremely low resistivity and a strong blue near-band-gap photoluminescence (PL) emission (~4610 A) without any deep broad emissions at room temperature. At lower Ga-cell temperatures, the carrier concentration and blue PL emission intensity increases significantly owing to an increase in substitutional Ga atoms acting as donors. At higher Ga-cell temperatures, an excess incorporation of Ga results in a reduction of carrier concentration, a decrease in blue PL emission, and a marked increase in deep broad emission (~5900 A).

Modeling semiconductor heterojunctions in equilibrium

Abstract: Computation of the equilibrium electrostatic potential and energy band diagram of semiconductor devices with nonuniform composition is considered. We first establish the relationship between the electrostatic potential and the energy band edges and then derive a Poisson-Boltzmann equation for the electrostatic potential. Although the equation is more general, we consider only the simple example of an abrupt heterojunction diode in detail. An analytical solution for doubly-intrinsic, abrupt heterojunctions is also presented. The modeling approach is then generalized to include Fermi-Dirac statistics for free carriers. We also discuss the application of the formulation to a variety of heterojunction devices (e.g. heavily doped silicon and gate-modulated devices).

Method of forming a semiconductor device on insulating substrate by selective amorphosization followed by simultaneous activation and reconversion to single crystal state

Abstract: A method for manufacturing a semiconductor device of a type in which a semiconductor element is formed on an insulating substrate. After ions which break the regularity of the crystal lattice of a monocrystalline semiconductor layer formed on the insulating substrate are implanted to form an amorphous semiconductor layer in part of the monocrystalline semiconductor layer, and after an impurity is doped in the semiconductor layer, a single annealing process is performed to recrystallize the amorphous semiconductor layer and at the same time to activate the doped impurity.