Showing papers on "Doping published in 1990"

p-type ZnSe by nitrogen atom beam doping during molecular beam epitaxial growth

Abstract: A novel approach to producing p‐type ZnSe epitaxial layers is reported which involves nitrogen atom beam doping during molecular beam epitaxial growth. Net acceptor concentrations as large as 3.4×1017 cm−3 have been measured in nitrogen atom beam doped ZnSe/GaAs heteroepitaxial layers which represents the highest acceptor concentration reported to date for ZnSe:N epitaxial material grown by molecular beam epitaxy. In addition, light‐emitting diodes based on ZnSe:N/ZnSe:Cl, p‐n homojunctions have been found to exhibit dominant electroluminescence in the blue region of the visible spectrum at room temperature.

Anisotropic Etching of Crystalline Silicon in Alkaline Solutions II . Influence of Dopants

Abstract: The etching behavior of highly boron doped silicon in aqueous solutions based of ethylenediamine, KOH, NaOH, and LiOH was studied. For all etchants, a strong reduction of the etch rate for boron concentrations exceeding approximately 2 �9 10 ~9 cm -3 was observed. This value is in good agreement with published data for the onset of degeneracy of p-type silicon. The reduction of the etch rate was found to be inversely proportional to the fourth power of the boron concentration. For a given high boron concentration, the etch stop effect was found to be most effective for ethylenediamine-based solutions and low concentration KOH and least effective for highly concentrated KOH. On the basis of these results, a model is proposed attributing the etch stop phenomenon to electrical effects of holes rather than chemical effects of boron. Due to the high dopant concentration the width of the space charge layer on the silicon surface shrinks drastically. Therefore, electrons injected into the conduction band by an oxidation reaction cannot be confined to the surface and rapidly recombine with holes from the valence band. The lack of these electrons impedes the reduction of water and thereby the formation of new hydroxide ions at the silicon surface. Since the transfer of four electrons is required for the dissolution of one silicon atom the observed fourth power law for the decrease of the etch rate can be explained. The reduction of the etch rate on silicon doped with germanium or phosphorus is much smaller and follows a different mechanism.

Structural chemistry and the local charge picture of copper oxide superconductors.

Abstract: The crystal structures of the known copper oxide superconductors are described, with particular emphasis on the manner in which they fall into structural families. The local charge picture, a framework for understanding the influence of chemical composition, stoichiometry, and doping on the electrical properties of complex structures, is also described.

Carrier dynamics of electrons and holes in moderately doped silicon.

Abstract: A time-domain spectroscopic technique, based on the generation and detection of a collimated beam of subpicosecond broadband terahertz pulses, is used to measure the absorption and dispersion of n- and p-type silicon, with resistivities of 0.1, 1, and 10 \ensuremath{\Omega} cm in the submillimeter range of 0.1--2 THz. From the transmission measurements performed at room temperature and at 80 K, the absorption and dispersion, and concomitantly the full complex conductivity, of the doped silicon could be obtained. The results provide an accurate view on the dynamics of the electrons and the holes. Although the simple Drude model, with an energy-independent relaxation time, gives a surprisingly accurate description of the observed carrier dynamics, the measurements do show that some refinements are needed. An extended model, with an energy-dependent carrier-relaxation rate, can explain most of the observed deviations from the simple Drude model.

Delta doping of III–V compound semiconductors: Fundamentals and device applications

Abstract: Delta‐function‐like doping profiles can be obtained in semiconductors by growth‐interrupted impurity deposition during molecular‐beam epitaxy. The spatial localization of dopants is assessed by the capacitance–voltage profiling technique and secondary ion mass spectroscopy which yield profile widths of 20 and 37 A for Be δ‐doped GaAs grown at 500 °C, respectively. The diffusion coefficients of Si, Be, and C in GaAs and of Si in AlxGa1−xAs are determined and diffusion is shown to be negligible at low growth temperatures. At elevated growth temperatures, dopant redistribution occurs during epitaxial growth. The redistribution is shown to be due to (i) diffusion of dopants and (ii) Fermi‐level pinning induced segregation of dopants along the growth axis. Fermi‐level pinning induced segregation of dopants is a novel mechanism which results in a redistribution of dopants predominantly toward the growing surface due to electrostatic attraction of dopants and carriers localized in surface states. This mechamism is shown to be relavant at elevated growth temperatures of ≥600 °C. Electronic devices such as homostructure and heterostructure field‐effect transistors which employ the δ‐doping technique have a number of advantages including (i) high carrier density, (ii) proximity between electron channel and gate electrode, (iii) large breakdown voltage of the gate, and (iv) reduced short‐channel effects. In addition, high transconductances are obtained in such δ‐doped field‐effect transistors. The optical properties of doping superlattices are significantly improved using the δ‐doping technique. Quantum‐confined interband transitions in doping superlattices are observed for the first time in such improved doping superlattices. Furthermore, a tunable doping superlattice laser is demonstrated, which has a tuning range of 35 A. The tunable doping superlattice laser has a potential tuning range of 220 A and is a candidate for a tunable source in future optical communication systems.

Studies of diffused phosphorus emitters: saturation current, surface recombination velocity, and quantum efficiency

Abstract: The surface recombination velocity s for silicon surfaces passivated with thermal oxide was experimentally determined as a function of surface phosphorus concentration for a variety of oxidation, anneal, and surface conditions. This was accomplished by measuring the emitter saturation current density J/sub 0/ of transparent diffusions for which the J/sub 0/ is strongly dependent on s. At the lowest doping levels, the value of s was confirmed by measurements of s on substrates with uniform phosphorus doping. The impact of these measurements on solar cell design is discussed. >

Structure and Electrical Properties of Polyacetylene Yielding a Conductivity of 10 5 S/cm

Abstract: We have prepared polyacetylene (ν-(CH)x) yielding a conductivity of more than 105 S/cm, by making some modifications on Naarmann et al.'s method. Structural analyses of this polymer were carried out by use of various analysis techniques such as SEM, IR and resonance Raman spectroscopy to characterize ν-(CH)x. No distinct differences in structure between conventional polyacetylene and ν-(CH)x were observed except for morphology and specific gravity. Upon iodine doping, conductivity increases stepwisely, which may suggest the formation of a staging structure and/or the transformation to metallic phase. However, in the temperature dependence of conductivity, we could not find any differences which distinguish the metallic ν-(CH)x from conventional polyacetylene.

Amorphous silicon memory

Abstract: An analogue memory device comprises a layer of doped amorphous silicon located between a first conducting layer metal contact layer of V, Co, Ni, Pd, Fe or Mn. It has been found that the selection of one of these metals as the contact exerts a significant effect on the properties of the device, e.g. the selection of Al, Au or Cu gives no switching whereas Cr, W, Ag give digital instead of analogue switching.

Growth and Luminescence Properties of Mg‐Doped GaN Prepared by MOVPE

Abstract: Growth and luminescence properties of Mg‐doped prepared by metal‐organic vapor phase epitaxy, in which or is used as the Mg source gas, are reported for the first time. It was found that the Mg concentration in is proportional to the flow rate of the Mg source gas; the doping efficiency of Mg into is independent of the substrate temperature from 850° to 1040°C; and Mg in acts as an acceptor and forms blue luminescence centers. By using, an efficient near‐UV and blue LED can be fabricated.

The effect of surface treatment on the electrical properties of metal contacts to boron-doped homoepitaxial diamond film

Abstract: Both doped and undoped homoepitaxial diamond films were fabricated using microwave plasma-enhanced chemical vapor deposition (CVD). The conductivity of the diamond film is strongly affected by the surface treatment. In particular, exposure of film surface to a hydrogen plasma results in the formation of a conductive layer which can be used to obtain linear (ohmic) I-V characteristics of the Au/diamond contacts, regardless of the doping level. It is shown how the proper chemical cleaning of the boron-doped homoepitaxial diamond surface allows the fabrication of Au-gate Schottky diodes with excellent rectifying characteristics at temperatures of at least 400 degrees C. >

Low and high temperature TiO2 oxygen sensors

Abstract: We have studied two types of TiO2-based oxygen sensors operating at different temperatures with different detection principles At high temperatures, TiO2 devices can be used as thermodynamically controlled bulk defect sensors to determine oxygen over a large range of partial pressures Their intrinsic behaviour can be controlled by carefully directed doping with tri- or pentavalent cations At low temperatures, we find that Pt/TiO2 Schottky diodes make extremely sensitive oxygen detection possible The latter show reversible shifts of current-voltage curves, which are determined by interface states formed by chemisorbed oxygen

Self-aligned overlap MOSFET and method of fabrication

Abstract: A high speed submicron transistor which exhibits a high immunity to hot electron degradation and is viable for VLSI manufacturing. An inner gate member is formed on a p type substrate. A first source region and a first drain region are disposed in the p type substrate in alignment with the inner gate member for forming a lightly doped region. A conductive spacer is formed adjacent to and is coupled to each side of the inner gate member on the gate oxide layer for forming a gate member which overlaps the lightly doped region. A second source region and a second drain region are disposed in the first source region and first drain regions, respectively, self-aligned with the outer edges of the conductive spacers to form source and drain contact areas.

Properties of Boron-Doped Epitaxial Diamond Films

Abstract: Boron-doped homo-epitaxial films were deposited by microwave plasma CVD on synthesized single-crystal diamonds. Boron concentration in the films was determined by the boron concentration in the reactant gases. The crystallinity of boron- doped films was found to be affected by the boron concentration in the reactant gases. The conductivity of boron doped films was determined by the concentration of boron, and the activation energy was nearly the same as for natural IIb diamonds. The effect of the surface orientation of substrates was found in the conductivity of highly doped films. The result of the Hall effect measurement indicated that the mobility of boron-doped diamond epitaxial films was 70 cm2/Vs even at 500°C.

A thermally activated solid state reaction process for fabricating ohmic contacts to semiconducting diamond

Abstract: Techniques have been developed to produce ohmic contacts to naturally occurring boron doped semiconducting diamond. Thin films of Mo, Mo/Au, and Mo/Ni/Au deposited on diamond produced adherent ohmic contacts after annealing at 950 °C. A thermally activated solid state reaction which produces a refractory carbide precipitate at the original diamond/metal interface is the principal factor in affecting the properties of the contacts. The interface reaction has been characterized using Auger electron spectroscopy, scanning electron microscopy, x‐ray diffraction, metallography, and I‐V measurements.

Effects of energy transfer among Er 3+ ions on the fluorescence decay and lasing properties of heavily doped Er:Y 3 Al 5 O 12

Abstract: Nonexponential fluorescence decay has been observed from both 4I11/2 and 4I13/2 states of Er3+ ions in heavily doped Er: YAG at room temperature. Processes of cross relaxation that originate in these states are shown to be responsible. Rate equations that include cross-relaxation processes are written and numerically solved, to result in the determination of the cross-relaxation coefficients. It is found that these coefficients do not change with Er3+ concentration. The effects of the cross-relaxation processes of Er3+ ions on fluorescence decay and lasing properties are discussed.

Boron-related deep centers in 6H-SiC

Abstract: 6H-silicon carbide layers are grown by a liquid phase epitaxy (LPE) process. The layers are doped with boron either by ion implantation or during the LPE process from a B-doped silicon melt. Deep-level transient spectroscopy (DLTS), admittance spectroscopy and photoluminescence (PL) are used to investigate deep impurity centers. Two electrically active defect centers are detected: the isolated boron acceptor at EB=Ev+0.3eV and the boron-related D-center at ED=Ev+0.58eV. The yellow luminescence observed in these layers is proposed to be due to pair recombination via D-center and nitrogen donor. Formation and origin of the D-center are discussed.

Hole relaxation and luminescence polarization in doped and undoped quantum wells.

Abstract: Valence-hole relaxation by acoustic-phonon emission yields spin relaxation through the spin mixing of the hole-band states. In quantum wells, the hole-spin relaxation is incomplete. This leads to a unified theory of the polarization spectra for undoped and doped quantum wells, which explains the diverse features in the spectra.

Phonon sideband of Eu3+ in sodium borate glasses

Abstract: The phonon sideband (PSB) of Eu3+ associated with the 7F0-5D2 transition was investigated for the B2O3Na2O glasses doped with 1 mol% Eu2O3. It was found that the coupling of the phonon mode with Eu3+ ions in the glasses was through B-O− or B-O stretching vibration of BO3 units and vibrations of BO4− units in tetra- and diborate groups. The results showed that B-O− bonds present around Eu3+ ions, which have the highest phonon energy, contributed to the nonradiative decay by multiphonon relaxation of Eu3+ ions even in low-alkali borate glasses. Moreover, the electron-phonon coupling strength of each borate group was found to be influenced by the fraction present and by the site selectivity of Eu3+ ions for the group.

Preparation of Small-Particle-Size, Semiconductor CdS-Doped Silica Glasses by the Sol–Gel Process

Abstract: The sol–gel process has been applied successfully to the preparation of small-particle-size CdS-doped silica glasses with a significant quantum size effect. Gels prepared through the hydrolysis of a complex solution of Si(OC2H5)4 and Cd(CH3COO)2·2H2O were heated at 500°C, then reacted with H2S gas to form fine, hexagonal, CdS-microcrystal-doped glasses. The optical absorption edge is blue shifted by ∼0.4 eV compared with the bulk absorption value of CdS crystal. This result is interpreted in terms of a quantum-confinement effect of small crystal size.

Role of band-tail carriers in metastable defect formation and annealing in hydrogenated amorphous silicon

Abstract: This paper presents results on annealing of carrier-induced metastable defects in hydrogenated amorphous silicon ({ital a}-Si:H) and on the dependence of the defect kinetics on carrier density. The metastable defects were studied by measuring the threshold-voltage shifts on capacitors as a function of time, temperature, and bias. The defect generation and annealing exhibit stretched-exponential-like behavior where the characteristic time for defect generation is a function of carrier density. The ratio of carrier density to defects in equilibrium are determined to be approximately 0.1, the same ratio found in doped {ital a}-Si:H. The results are consistent with dispersive hydrogen motion through an exponential distribution of barrier heights. The hopping rate and the final-state energy depend on the carrier density. This dependence on carrier density explains the carrier-, light-, and doping-induced defect formation in {ital a}-Si:H. The increase of the hopping rate due to carriers accounts for the increase in the hydrogen-diffusion rate in doped material. While much of the data are consistent with a single-hop model, the lack of correlation between generation and annealing rates indicates that defect formation occurs by multiple hopping.

Cathodoluminescence and electroluminescence of undoped and boron-doped diamond formed by plasma chemical vapor deposition

Abstract: Visible luminescence between 2.0–3.5 eV of undoped and boron‐doped diamond formed by plasma‐assisted chemical vapor deposition has been investigated by cathodoluminescence. Electroluminescence from Schottky diode of boron‐doped semiconducting diamond has been observed for the first time and found to be due to the same luminescent center as that of cathodoluminescence. In the particles or films where the content of nitrogen and boron was greatly reduced, the cathodoluminescence peaks occurred at 2.8–2.9 eV. The characteristics of these emission spectra are very similar to those obtained in type‐IIa diamond where dislocations are luminescent. The doping of boron during the deposition form another luminescent center at 2.3–2.4 eV. From the monochromatic cathodoluminescence imaging, the luminescent regions differ in the two peaks. {100} sectors are much more luminescent than {111} sectors at the signal of 2.8 eV. This phenomenon has been discussed based on the difference in defect or impurity concentration of...

Band tails in hydrogenated amorphous silicon and silicon-germanium alloys.

Abstract: The temperature dependence of the conduction- and valence-band tails has been determined by total-photoelectron-yield spectroscopy for doped and undoped a-Si:H and a-SiGe:H alloys. All films possess purely exponential conduction- and valence-band-tail densities of states; however, the characteristic energy of the conduction-band tail increases much more rapidly with temperature than that of the valence-band tail. The conduction-band tail is considerably more susceptible to thermal disorder than to structural disorder, whereas the reverse holds for the valence-band tail

Crystal structure of (Bi, Pb)2Sr2Can−1CunO4+2n+δ high-Tc superconductors

Abstract: The crystal structure of (Bi, Pb)2Sr2Can−1CunO4+2n+δ high-temperature superconducting phases was studied by transmission electron microscopy. The displacive modulation is largest for the n=1 material and yields displacement amplitudes of 70 pm with respect to the average structure. In all phases the largest distortions are found in the Bi-O double layers. The structural distortions were determined explicitly for the cations and amplitudes for the atomic modulation functions are given for the n=1 and n=2 phases. For Bi2Sr2CaCu2O8+δ(Tc=85 K) the space group Pbnb was determined for the average structure and accounts for reflections which cannot be indexed by Bbmb. In material doped with Pb the periodicity of the modulation changes significantly, from 4.7 times the lattice parameter b for the undoped phases to 8b for the doped n=2 phase and 8.8b for the doped n=3 phase, respectively. For the doped phases systematic extinction conditions are compatible with the space group PBb1m1b1. Due to the modulation, shifts of atoms may lead to distortions of CuO polyhedra and should effect the electronic structure of the various phases.