Showing papers on "Doping published in 1996"

Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p-n Junction.

Abstract: Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of poly(1,4-phenylenevinylene) and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. The cells contain three layers: the polymer film (as the emissive layer) and indium-tin oxide and aluminum films as the two contact electrodes. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a light-emitting p-n junction is formed in between. The admixed polymer electrolyte provides the counterions and the ionic conductivity necessary for doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the band gap of the redox-active conjugated polymer (2.4 eV for PPV). Green light emitted from the p-n junction was observed with a turn-on voltage of about 2.4 V. The devices reached 8 cd/m(2) at 3 V and 100 cd/m(2) at 4 V, with an external quantum efficiency of 0.3-0.4% photons/electron. The response speed of these cells was around 1 s, depending on the diffusion of ions. Once the light-emitting junction had been formed, the subsequent operation had fast response (microsecond scale or faster) and was no longer diffusion-controlled.

Low-threshold cold cathodes made of nitrogen-doped chemical-vapour-deposited diamond

Abstract: BECAUSE diamond surfaces terminated with hydrogen have a negative electron affinity1–4 (the conduction band minimum lies below the vacuum level), they are expected to emit electrons spontaneously. This has led to attempts to develop 'cold cathodes'—miniaturized vacuum diodes that might have applications in microelectronics and flat-panel displays. In previous studies of electron emission from diamond grown by chemical vapour deposition5–9 (CVD), the threshold voltages for emission were more than an order of magnitude too large for use in battery-driven cold cathodes. Although low-threshold emission from caesium-coated, nitrogen-doped high-pressure synthetic diamond was reported recently10, ultimately diamond thin films grown by chemical vapour deposition (CVD) look to be the most promising material for cold-cathode applications. But to obtain low-threshold emission, it is necessary to introduce high concentrations of donor dopants such as nitrogen—something that is difficult for CVD diamond. Here we report that high concentrations of nitrogen can be incorporated into diamond films by using urea as the gaseous nitrogen source, and that such heavily doped films shown very-low-threshold electron emission, which augurs well for cold-cathode technology.

Activation of acceptors in Mg-doped GaN grown by metalorganic chemical vapor deposition

Abstract: The activation kinetics of acceptors was investigated for heteroepitaxial layers of GaN, doped with Mg. After growth, the samples were exposed to isochronal rapid thermal anneals in the temperature range from 500 to 775 °C. The samples were studied by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy in the as‐grown condition and after each temperature step. The thermal treatment reduced the resistivity by six orders of magnitude and the p‐type conductivity was found to be dominated by an acceptor with an activation energy of ∼170 meV. This acceptor is attributed to Mg atoms substituting for Ga in the GaN lattice and the activation process is consistent with dissociation of electrically inactive Mg–H complexes. It is shown that the appearance of a blue emission band in the PL spectrum of Mg‐doped GaN does not directly correlate with the increase in p‐type conductivity.

Activation energies of si donors in gan

Abstract: The electronic properties of Si donors in heteroepitaxial layers of GaN were investigated. The n‐type GaN layers were grown by metalorganic chemical vapor deposition and either intentionally doped with Si or unintentionally doped. The samples were evaluated by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy. For both types of samples the n‐type conductivity was found to be dominated by a donor with an activation energy between 12 and 17 meV. This donor is attributed to Si atoms substituting for Ga in the GaN lattice (SiGa). The range of activation energies is due to different levels of donor concentrations and acceptor compensation in our samples. The assignment of a PL signature to a donor–acceptor pair recombination involving the Si donor level as the initial state of the radiative transition yields the position of the optical Si donor level in the GaN bandgap at ∼Ec–(22±4) meV. A deeper donor level is also present in our GaN material with an activation energy of ∼3...

Very high breakdown voltage and large transconductance realized on gan heterojunction field effect transistors

Abstract: We report record high breakdown voltages up to 340 and 230 V realized on unintentionally doped (1.5 μm gate length) and Si doped (1 μm gate length) AlGaN/GaN modulation doped field effect transistors (MODFETs), respectively. The devices also have large transconductances up to 140 mS/mm and a full channel current of 150–400 mA/mm. The Si doped MODFET sample demonstrated a very high room temperature mobility of 1500 cm2/Vs. With these specifications, GaN field effect transistors as microwave power devices are practical.

Role of hydrogen in doping of GaN

Abstract: We investigate the interactions between hydrogen and dopant impurities in GaN, using state‐of‐the‐art first‐principles calculations. Our results for energetics and migration reveal a fundamental difference in the behavior of hydrogen between p‐type and n‐type material; in particular, we explain why hydrogen concentrations in n‐type GaN are low, and why hydrogen has a beneficial effect on acceptor incorporation in p‐type GaN. Our results identify the conditions under which hydrogen can be used to control doping in semiconductors in general.

Red-Emitting Semiconductor Quantum Dot Lasers

Abstract: Visible-stimulated emission in a semiconductor quantum dot (QD) laser structure has been demonstrated. Red-emitting, self-assembled QDs of highly strained InAlAs have been grown by molecular beam epitaxy on a GaAs substrate. Carriers injected electrically from the doped regions of a separate confinement heterostructure thermalized efficiently into the zero-dimensional QD states, and stimulated emission at ∼707 nanometers was observed at 77 kelvin with a threshold current of 175 milliamperes for a 60-micrometer by 400-micrometer broad area laser. An external efficiency of ∼8.5 percent at low temperature and a peak power greater than 200 milliwatts demonstrate the good size distribution and high gain in these high-quality QDs.

Gallium nitride-based III-V group compound semiconductor

Abstract: A gallium nitride-based III-V Group compound semiconductor device has a gallium nitride-based III-V Group compound semiconductor layer provided over a substrate, and an ohmic electrode provided in contact with the semiconductor layer. The ohmic electrode is formed of a metallic material, and has been annealed.

Novel oxide amorphous semiconductors: transparent conducting amorphous oxides

Abstract: A working hypothesis to find wide gap oxide semiconductors was proposed on the basis of simple considerations. The hypothesis predicts that amorphous double oxides composed of heavy metal cations (HMCs) with an electronic configuration (n − 1)d10s0 are promising candidates for a novel class of amorphous semiconductors. Electrical and optical properties of three amorphous double oxides composed of the HMCs, a-AgSbO3, Cd2GeO4 and Cd2PbO4, were examined, following this hypothesis. It was found that when carrier electrons are generated via the formation of oxygen vacancies or doping of excess cations by ion implantation, these three wide band gap amorphous oxides show high electrical conductivities of 10−1 to 102 S cm−1 at ∼ 300 K and the conductivity remains almost constant down to 77 or 4 K for high carrier concentrations (> 1018 cm−3). This high conductivity originates primarily from a large Hall mobility of ∼ 10 cm2 V−1 s−1, which is higher by several orders of magnitude than that in amorphous transition metal oxides, Si:H and chalcogenides. A variety of chemical compositions for a novel oxide amorphous semiconductor are suggested.

Memory cell incorporating a chalcogenide element and method of making same

Abstract: A memory cell incorporating a chalcogenide element and a method of making same is disclosed. In the method, a doped silicon substrate is provided with two or more polysilicon plugs to form an array of diode memory cells. A layer of silicon nitride is disposed over the plugs. Using a poly-spacer process, small pores are formed in the silicon nitride to expose a portion of the polysilicon plugs. A chalcogenide material is disposed in the pores by depositing a layer of chalcogenide material on the silicon nitride layer and planarizing the chalcogenide layer to the silicon nitride layer using CMP. A layer of TiN is next deposited over the plugs, followed by a metallization layer. The TiN and metallization layers are then masked and etched to define memory cell areas.

Method for the stabilization of halogen-doped films through the use of multiple sealing layers

Abstract: A method and apparatus for depositing a halogen-doped oxide film having a low dielectric constant that is resistant to moisture absorption and outgassing of the halogen dopant, and that retains these qualities despite subsequent processing steps. The method begins by introducing process gases (including a halogen-containing source gas) into a processing chamber. A halogen-doped layer is then deposited. The combination of process gases is then changed and a sealing layer deposited which seals the dopant into the halogen-doped layer. The sealing layer may, for example, be a carbon-rich layer or an undoped layer. These steps are repeated until the film reaches a selected thickness.

Surface recombination velocity of highly doped n-type silicon

Abstract: New experimental data for the minority‐carrier surface recombination velocity of n‐type silicon, Sp, are reported. The data, obtained from photoconductance decay measurements of the recombination currents corresponding to different phosphorus diffusions, include oxide‐passivated, unpassivated and metal‐coated surfaces. For the passivated case, Sp increases linearly with surface dopant density, ND, for dopant densities higher than 1×1018 cm−3, while for unpassivated (bare) and for metal‐coated silicon Sp remains essentially constant, at about 2×105 cm/s and 3×106 cm/s, respectively. The experiments also allow for a determination of the apparent energy bandgap narrowing as a function of dopant density, ΔEgapp=14 meV [ln(ND/1.4×1017 cm−3)]. These surface recombination velocity and ΔEgapp data form, together with the dependences of minority‐carrier lifetime, τp, and mobility, μp, used in the analysis, a consistent set of parameters that fully characterize highly doped n‐type silicon.

Electron mobility in two-dimensional electron gas in AlGaN/GaN heterostructures and in bulk GaN

Abstract: We report on temperature dependencies of the electron mobility in the two-dimensional electron gas (2DEG) in AIGaN/GaN heterostructures and in doped bulk GaN. Calculations and experimental data show that the polar optical scattering and ionized impurity scattering are the two dominant scattering mechanisms in bulk GaN for temperatures between 77 and 500K. In the 2DEG in AIGaN/GaN heterostructures, the piezoelectric scattering also plays an important role. Even for doped GaN, with a significant concentration of ionized impurities, a large volume electron concentration in the 2DEG significantly enhances the electron mobility, and the mobility values close to 1700 cm2/Vs may be obtained in the GaN 2DEG at room temperature. The maximum measured Hall mobility at 80K is nearly 5000 cm2/Vs compared to approximately 1200 cm2/Vs in a bulk GaN layer. With a change in temperature from 300 to 80K, the 2DEG in our samples changes from nondegenerate and weakly degenerate to degenerate. Therefore, in order to interpret the experimental data, we propose a new interpolation formula for low field mobility limited by the ionized impurity scattering. This formula is valid for an arbitrary degree of the electron gas degeneracy. Based on our theory, we show that the mobility enhancement in the 2DEG is related to a much higher volume electron concentration in the 2DEG, and, hence, to a more effective screening.

Simultaneous deposit and etch method for forming a void-free and gap-filling insulator layer upon a patterned substrate layer

Abstract: A method for forming a void-free and gap-filling doped silicon oxide insulator layer upon a patterned substrate layer within an integrated circuit. Formed upon a semiconductor substrate is a patterned substrate layer. Formed upon the patterned substrate layer is a doped silicon oxide insulator layer. The doped silicon oxide insulator layer is formed through a Plasma Enhanced Chemical Vapor Deposition (PECVD) deposition method undertaken simultaneously with a Reactive Ion Etch (RIE) etch-back method. The Plasma Enhanced Chemical Vapor Deposition (PECVD) deposition method and the Reactive Ion Etch (RIE) etch-back method simultaneously employ a Tetra Ethyl Ortho Silicate (TEOS) silicon source material, a dopant source material, an oxygen source material and an etching gas.

Correlation between Free Volume and Ionic Conductivity in Fast Ion Conducting Glasses.

Abstract: It is well known that fast ionic conductivity can be obtained by doping modified oxide glasses with a metal-halide salt. The role of the dopant salt, apart from providing additional charge carriers, for the ionic conductivity has been a much debated issue. Using conductivity and density data for different host glasses mixed with various metal-halide salts, we find a remarkable common cubic scaling relation between the conductivity enhancement and the expansion of the network forming units induced by salt doping. This suggests that the glass network expansion, which is related to the available free volume, is a key parameter determining the increase of the high ionic conductivity in this type of fast ion conducting glasses. [S0031-9007(96)01369-5] High room temperature ionic conductivity in solid materials is technologically interesting for various solid state electrochemical devices, e.g., batteries, “smart windows”. Apart from some exotic crystalline materials such as Rb4AgI5, the highest ionic conductivity at room temperature has been observed in some salt doped oxide, sulfur, and halide glasses. The salt doped oxide glasses are particularly interesting for applications because of their ease of preparation, their stability, and the large available composition ranges, and have also become model materials for investigations of diffusion in disordered solids.

Dielectric Activity and Ferroelectricity in Piezoelectric Semiconductor Li-Doped ZnO

Abstract: Temperature dependences of dielectric constants, specific heat and D–E hysteresis loops of Li-doped zinc oxide ceramics were investigated. A new dielectric anomaly was found at 330 K in Zn1-xLixO with x=0.17. A cusp-like anomaly was also found in specific heat. A ferroelectric D–E hysteresis loop was successfully observed for the first time. These observations suggest that replacement of host Zn ions by small Li ions induces a ferroelectric phase in the wurtzite-type ZnO piezoelectric semiconductor. This material is a candidate for ferroelectric thin films in integrated ferroelectric devices.

Semiconductor laser having a structure of photonic bandgap material

Abstract: Disclosed is a semiconductor laser that is constituted by at least one active layer sandwiched between two confinement layers with P and N type doping to constitute a PN junction. In at least one of the confinement layers and/or the active layer, holes are designed on each side of the cavity so as to form structures of photonic bandgap material along the lateral walls of the cavity and the ends of the cavity.

Stable and efficient electroluminescence from a porous silicon‐based bipolar device

Abstract: A complete process compatible with conventional Si technology has been developed in order to produce a bipolar light‐emitting device. This device consists of a layer of light‐emitting porous silicon annealed at high temperature (800–900 °C) sandwiched between a p‐type Si wafer and a highly doped (n+) polycrystalline Si film. The properties of the electroluminescence (EL) strongly depend on the annealing conditions. Under direct bias, EL is detected at voltages of ∼2 V and current densities J∼1 mA/cm2. The maximum EL intensity is 1 mW/cm2 and the EL can be modulated by a square wave current pulse with frequencies ν≥1 MHz. No degradation has been observed during 1 month of pulsed operation.

Si-Ge CMOS semiconductor device

Abstract: To obtain a high mobility and a suitable threshold voltage in MOS transistors with channel dimensions in the deep sub-micron range, it is desirable to bury a strongly doped layer (or ground plane) in the channel region below a weakly doped intrinsic surface region, a few tens of nm below the surface. It was found, however, that degradation of the mobility can occur particularly in n-channel transistors owing to diffusion of boron atoms from the strongly doped layer to the surface, for example during the formation of the gate oxide. To prevent this degradation, a thin layer 11 of Si 1−x Ge x inhibiting boron diffusion is provided between the strongly doped layer 10 and the intrinsic surface region 7 , for example with x=0.3. The SiGe layer and the intrinsic surface region may be provided epitaxially, the thickness of the SiGe layer being so small that the lattice constants in the epitaxial layers do not or substantially not differ from those in the substrate 1 in a plane parallel to the surface, while a sufficient diffusion-inhibiting effect is retained. Since SiGe has a diffusion-accelerating rather than decelerating effect on n-type dopants, the ground plane of a p-channel transistor in a CMOS embodiment is doped with As or Sb because of the low diffusion rate of these elements in pure silicon.

The effect of Pt and Pd surface doping on the response of nanocrystalline tin dioxide gas sensors to CO

Abstract: SnO2 sensors were prepared by precipitating Sn(OH)4 from an aqueous solution of SnCl4 or by evaporating SnO2 in the UHV. Subsequent X-ray and TEM measurements show grain sizes in the nanometer range after annealing at different temperatures or annealing times. The effect of Pt and Pd doping upon the response to CO is studied. Parameters, which we focused on, are sensor signal dependent on the operating temperature and dependent on the gas concentration. The results for ceramic sensors are compared with those for thin film sensors.

Electroluminescence of erbium–oxygen‐doped silicon diodes grown by molecular beam epitaxy

Abstract: We have fabricated erbium–oxygen‐doped silicon light emitting diodes with molecular beam epitaxy by simultaneously evaporating erbium and silicon and providing a suitable background pressure of oxygen. In reverse bias, the diodes show intense room‐temperature electroluminescence at λ=1.54 μm, originating from the intra‐4f transition of erbium. This luminescence does not show temperature quenching between 4 and 300 K. In forward bias the erbium peak intensity is reduced by a factor of 30 at low temperatures and shows temperature quenching.

Enhancement of deep acceptor activation in semiconductors by superlattice doping

Abstract: The thermal activation of acceptors in wide‐gap semiconductors can be very low due to large acceptor activation energies. It is shown that superlattice doping, i.e., the composition modulation of a uniformly doped ternary semiconductor, can enhance the acceptor activation by more than one order of magnitude.

Porous silicon as a sacrificial material

Abstract: Porous silicon is emerging in micromachining technology as an excellent material for use as a sacrificial layer. This is largely due to the ease of fabrication and freedom of design it allows. The rate of pore formation is heavily dependent upon the doping type and concentration of the silicon, allowing patterned porous silicon formation through selective doping of the substrate. Etch-rates above have been reported for highly doped material. Silicon that has been made porous can be quickly and easily removed in a dilute hydroxide solution, as low as 1%. Porous silicon technology offers the unique ability to fabricate free-standing structures in single-crystal silicon with separation distances from the substrate ranging from a few microns to over one hundred microns. A review of the development of porous silicon for micromachining applications is given.

Deep levels in the upper band-gap region of lightly Mg-doped GaN

Abstract: Deep levels in undoped and weakly Mg‐doped n‐type GaN films fabricated by metalorganic chemical vapor deposition were examined with deep level transient spectroscopy. Deep levels measured at 0.26 and 0.62 eV below the conduction band were found in relatively low concentrations of ∼2×1013 cm−3 in undoped GaN. Addition of small quantities of the Mg acceptor species by means of bis‐cyclopentadienyl magnesium (Cp2Mg) during growth corresponded to a significant increase in the concentration of the level at 0.62 eV. The concentration of the shallower level, found to be independent of the Cp2Mg addition, remained unchanged. These deep levels may detrimentally affect optical and electrical properties when fabricating p‐type GaN.

SiC semiconductor device comprising a pn junction with a voltage absorbing edge

Abstract: A semiconductor component, which comprises a pn junction, where both the p-conducting and the n-conducting layers of the pn junction constitute doped silicon carbide layers and where the edge of at least one of the conducting layers of the pn junction, exhibits a stepwise or uniformly decreasing total charge or effective surface charge density from the initial value at the defined working junction to a zero or almost zero total charge at the outermost edge of the junction following a radial direction from the central part of the junction towards the outermost edge.

Lid assembly for high temperature processing chamber

Abstract: PROBLEM TO BE SOLVED: To provide cleaning system/method/device, which form a dielectric film having the uniformity of thickness, satisfactory gap filling performance, high density and low moisture and have high temperature deposition/heating and satisfactory efficiency. SOLUTION: In a chamber with the pressure of about 100-760Torr, a method for forming the ultra-thin dope area of a substrate is used in the chamber containing a process for depositing a doped silicon oxide film containing dopant atoms on the substrate on a heater whose temperature is at least 500 deg.C from the reaction of silicon, oxygen and dopant and a process for heating the doped silicon oxide film for diffusing the dopant atoms in the substrate and forming the ultra-thin dope area.

Electron beam induced current measurements of minority carrier diffusion length in gallium nitride

Abstract: Minority carrier diffusion length in epitaxial GaN layers was measured as a function of majority carrier concentration and temperature. The diffusion length of holes in n‐type GaN is found to decrease from 3.4 to 1.2 μm in the doping range of 5×1015–2×1018 cm−3. The experimental results can be fitted by assuming the Einstein relation and by the experimental dependence of hole mobilities on carrier concentration. The low injection carrier lifetime of ∼15 ns, used in the fit, is largely independent of the doping level. The diffusion length, measured for ∼5×1015 and 2×1018 cm−3 dopant concentrations, shows an increase with increasing temperature, characterized by an activation energy Ea of ∼90 meV, independent of the impurity concentration.

Electrochemical behavior of boron-doped diamond electrodes

Abstract: Boron-doped diamond electrodes have many possibilities for electroanalytical and electrosynthetic application because of their stability and range. However, their combination of semiconductive origin, nearly metallic resistive characteristics when heavily doped, and surface inertness make the understanding of electron transfer at these materials complex. The transition from reversible behavior, with a wide range of outer sphere redox couples with potentials positive of about -0.5 V vs. SCE, to extremely slow kinetics, with systems such as the halogen/halide couples, requires placing all the above properties in context. Experimental data pertaining to these issues and speculation concerning the controlling factors are discussed.