Showing papers on "Doping published in 1984"

Band-gap widening in heavily Sn-doped In 2 O 3

Abstract: In this paper we investigate the optical properties of evaporated films of doped semiconducting In2O3 in the 2-6-eV range, i.e., around the fundamental bandgap. The study serves two main purposes: to elucidate basic properties of a heavily n-doped semiconductor, and to improve our understanding of a technologically important material which is widely used when transmittance of visible or solar radiation needs to be combined with good electrical conduction or low thermal emittance.

Charge storage in doped poly(thiophene): Optical and electrochemical studies

Abstract: We present a new method of electrochemical polymerization of poly(thiophene) using dithiophene as the starting material, from which we obtain a high-quality film with a sharp interband absorption edge. An in situ study of the absorption spectrum during the electrochemical doping process has been carried out. In the dilute regime, the results are in detailed agreement with charge storage via bipolarons; weakly confined soliton pairs with confinement parameter $\ensuremath{\gamma}\ensuremath{\cong}0.1\ensuremath{-}0.2$. At the highest doping levels, the data are characteristic of the free-carrier absorption expected for a metal. From a parallel electrochemical voltage spectroscopy study, we find evidence of charge injection near the band edge and charge removal from the bipolaron gap states. In the dilute regime, the position of the chemical potential is consistent with charge storage in weakly confined bipolarons. The high Coulombic recovery over a charge-discharge cycle indicates that poly (thiophene) may be an excellent cathode-active material in battery applications.

Physics of amorphous silicon based alloy field‐effect transistors

Abstract: In this paper we develop a new theory to describe the characteristics of amorphous silicon based alloy field‐effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap. The current‐voltage and capacitance‐voltage characteristics are related to the basic material parameters such as the distribution of localized states in the energy gap, band mobility, device geometry, channel doping, and series resistances. Our analysis shows that an on current in excess of 2×10−7 A/μm gate width can be obtained with a 10‐μm gate length. We also demonstrate that even in the above threshold regime the field‐effect mobility is dependent on the gate voltage. Our theory can be used to optimize the design of amorphous silicon based alloy field‐effect transistors.

Limits on the open-circuit voltage and efficiency of silicon solar cells imposed by intrinsic Auger processes

Abstract: Auger recombination processes are shown to impose the most severe intrinsic bounds on the open-circuit voltage and efficiency of silicon solar cells. This applies for both heavily doped and lightly doped material. The upper bound on the open-circuit voltage of a 300- µm-thick silicon cell is 750 mV (AMO, 25°C) irrespective of substrate resistivity. This bound increases to 800 mV for a 20 µm thick cell but decreases to a maximum value of 720 mV for cells thicker than the corresponding minority carrier diffusion length. The corresponding practical bound on cell efficiency is estimated as 25 percent (AM1.5, 100 mW/cm2, 28°C).

Modulation doping in GexSi1−x/Si strained layer heterostructures

Abstract: We report the first observation of the modulation doping effect in Si/Ge0.2Si0.8 heterojunctions grown by molecular beam epitaxy. Peak hole mobilities of ∼3300 cm2 V−1 s−1 have been observed at 4.2 K. These values, although nonoptimum, are comparable to the best reported values for holes in Si/SiO2 inversion layers. Low temperature, angular dependent, Shubnikov–de Haas measurements have demonstrated the two‐dimensional nature of the hole gas and yield a surface carrier density of 3.5×1011 cm−2. From the temperature dependence of the Shubnikov–de Haas amplitudes a hole effective mass of 0.30±0.02mo has been derived. Identical measurements on n‐type heterojunctions having the same Ge content (x=0.2) have failed to show a sustained enhancement of mobility at low temperatures, indicating that ΔEv≫ΔEc.

Hydrogen-Evolving Solar Cells

Abstract: Sunlight is directly converted to chemical energy in hydrogen-evolving photoelectrochemical cells with semiconductor electrodes. Their Gibbs free energy efficiency of solar-to-hydrogen conversion, 13.3 percent, exceeds the solar-to-fuel conversion efficiency of green plants and approaches the solar-to-electrical conversion efficiency of the best p-n junction cells. In hydrogen-evolving photoelectrodes, electron-hole pairs photogenerated in the semiconductor are separated at electrical microcontacts between the semiconductor and group VIII metal catalyst islands. Conversion is efficient when the island diameters are small relative to the wave-lengths of sunlight exciting the semiconductor; when the island spacings are smaller than the diffusion length of electrons at the semiconductor surface; when the height of the potential energy barriers that separate the photogenerated electrons from holes at the semiconductor surface is raised by hydrogen alloying of the islands; when radiationless recombination of electron-hole pairs at the semiconductor-solution interface between the islands is suppressed by controlling the semiconductor surface chemistry; and when the semiconductor has an appropriate band gap (1.0 to 1.8 electron volts) for efficient solar conversion.

An investigation of the effect of graded layers and tunneling on the performance of AlGaAs/GaAs heterojunction bipolar transistors

Abstract: We present the results of theoretical and experimental studies of the heterojunction bipolar transistor. Our calculations are based on a new thermionic field-diffusion model which takes into account the dependence of the emitter efficiency on the height of the interface conduction band spike and tunneling across the spike. Based on this theory we derive analytical expressions for the current-voltage characteristics and relate the short-circuit common emitter current gain to the material parameters, doping levels, grading length, and device temperature. We demonstrate that the thermoemission transport across the interface spike limits the rate of increase in the collector current with the emitter-base voltage and, as a consequence, the maximum common emitter current gain. Tunneling also plays an important role, especially for abrupt heterojunctions. Our calculations reveal an important role played by grading of the composition of the emitter region in the vicinity of the heterointerface. Such grading decreases the barrier height at the interface and greatly enhances the emitter injection efficiency.

Refractive index of In1−xGaxAsyP1−y layers and InP in the transparent wavelength region

Abstract: We have measured the refractive index of InP and of liquid‐phase‐epitaxy–grown InGaAsP layers on InP in the transparent wavelength region using a Brewster‐angle method. The dependence of the refractive index on material composition and light wavelength has been investigated for near‐lattice‐matched samples and compared with theoretical models. We show that both an interband transition model and a single effective oscillator model can be used to calculate the refractive index if the parameters used in the calculations are chosen properly. We have also studied the variation with lattice mismatch by varying the growth temperature. We found that a lattice mismatch variation of 10−3 corresponds to a change in the refractive index of approximately 0.02 for λg=1.20 μm layer band gap at λ=1.30 μm wavelength. Finally, we have measured the refractive index of doped InP substrates and found refractive index reductions, due to doping, of up to 0.05.

High mobility hole gas and valence-band offset in modulation-doped p-AlGaAs/GaAs heterojunctions

Abstract: Modulation‐doped p‐AlGaAs/GaAs heterojunctions have been grown by molecular beam epitaxy. The effects of undoped AlGaAs spacer thickness on sheet carrier density and on Hall mobility have been investigated. A mobility of 97 000 cm2 V−1 s−1 has been obtained at 4.2 K for a sheet density of 1.7×1011 cm−2. This is the highest mobility reported for holes in III‐V compound semiconductors. A valence‐band offset of 210±30 meV was deduced for Al0.5Ga0.5As /GaAs heterojunctions.

Effect of heavy doping on the optical properties and the band structure of silicon

Abstract: We have measured by ellipsometry the dielectric constant of pure and heavily doped $n$- and $p$- type silicon from 1.8 to 5.6 eV. Both ion-implanted laser-annealed and bulk doped samples were used with concordant results. A red shift of the ${E}_{1}$ and ${E}_{2}$ critical-point energies, together with a decrease in the excitonic interaction at the ${E}_{1}$ energy, has been observed. These results are compared with first- and second-order perturbation-theory calculations of the effect of the impurities on the band structure of silicon.

Photoluminescence and excitation spectroscopy in heavily doped n- and p-type silicon

Abstract: Low-temperature photoluminescence and excitation spectroscopy measurements on heavily doped (up to 4\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) $n$- and $p$-type silicon are reported. From the luminescence spectra values for the optical and the reduced band gap are deduced and compared with theoretical calculations. The shrinkage of the reduced band gap follows an ${n}^{\frac{1}{3}}$ law for carrier concentrations $n$ above the critical Mott density. Both $n$- and $p$-type samples show an identical shift of the reduced gap, whereas the shift of the optical gap is different due to the different density-of-states masses for electrons and holes. From photoluminescence excitation spectra the position of the optical gap is determined independently. A good agreement of the data obtained by these selective absorption measurements with the results from conventional luminescence spectra is found.

X‐Ray Investigation of Boron‐ and Germanium‐Doped Silicon Epitaxial Layers

Abstract: The lattice strain in highly boron‐doped, highly germanium‐doped, and simultaneously boron‐and‐germanium‐doped epitaxial layers was investigated by means of x‐ray techniques. The lattice‐contraction coefficient was determined for both impurities, and was found to be for boron and for germanium doping. A simple linear superposition of calculated or experimentally determined lattice‐contraction coefficients obtained for layers doped with boron vs. those doped with germanium does not yield satisfactory results in estimating the germanium concentration necessary for strain compensation in highly boron‐doped layers. Strain‐compensated dislocation‐free epitaxial layers were fabricated with a boron concentration of , using a germanium concentration of .

Study of the atomic models of three donorlike defects in silicon metal‐oxide‐semiconductor structures from their gate material and process dependencies

Abstract: The atomic models of the generation and annealing of three donorlike defects [the bulk compensating donor, the donorlike interface density‐of‐state (DOS) peak, and the positive turn‐around charge] in silicon metal‐oxide‐semiconductor capacitors (MOSC) are investigated by studying their dependencies on the gate materials and process conditions. Starting thermal oxides used in this study include 1000 C dry oxides on 〈100〉 p‐Si substrates and 750 C high‐pressure steam oxides on 〈111〉 p‐Si substrates. Gate materials include aluminum, gold, and LPCVD (low‐pressure chemical‐vapor‐deposition) polycrystalline silicon (poly‐Si) with several doping methods. The densities of these donors generated during avalanche electron injection in MOSC’s with boron in situ doped LPCVD poly‐Si gates are smaller compared with those with aluminum gates. High temperature (>900 C) processes (diffusion or anneal) in dry inert gas after the poly‐Si gate deposition inhibit the generation of all three donors. After the inhibition, the d...

Narrow band gap photovoltaic devices with enhanced open circuit voltage

Abstract: The open circuit voltage and efficiency of photovoltaic devices formed from multiple regions of semiconductor alloys including at least one narrow band gap semiconductor alloy are enhanced. The device includes a pair of doped regions and an intrinsic body between the doped regions. The intrinsic body includes a first intrinsic region and an open circuit voltage enhancement means including a second intrinsic region. The second intrinsic region has a wider band gap than the band gap of the first intrinsic region and is disposed between the first intrinsic region and one of the doped regions. The open circuit enhancement means can also include a third intrinsic region also having a wider band gap than the first intrinsic region and disposed on the side of the first intrinsic region opposite the second intrinsic region.

Properties of amorphous semiconducting multilayer films

Abstract: The structural, optical, and electrical properties of amorphous multilayer films containing up to 180 double layers of a-Si:H/a-SiNx and a-Si:H/a-SiOx were studied. For a-Si:H layer thickness d >100 A the transport properties are dominated by space-charge doping with a-SiNx positive and a-SiOx negatively charged. For d A quantum-well effects increase the optical and electrical gaps. A d =12 A multilayer film shows no evidence for the predicted loss of extended states in two-dimensional disordered systems.

Theory of conduction in polysilicon: Drift-diffusion approach in crystalline-amorphous-crystalline semiconductor system—Part I: Small signal theory

Abstract: A theory of conduction in polycrystalline silicon is presented. The present approach fundamentally differs from previous theories in its treatment of the grain boundary. This theory regards the grain boundary as amorphous semiconductor in equilibrium contact with crystalline grain. The model explains the electrical properties of polysilicon in terms of the electronic and structural parameters of the material and is in excellent agreement with the experimental data. The formulation is applicable for arbitrary grain size, temperature, doping concentration, and applied voltage. Specifically, the temperature dependence of resistivity is explained in terms of conduction channels inherent in the amorphous grain boundary. Also, this paper explicitly compares the previous emission theories with the present model in terms of voltage partition scheme and I - V predictions.

Method of producing semiconductor device

Abstract: A method of producing a MOS transistor of LDD structure with p(n) type pockets. A doped oxide film in which impurities such as phosphorus and impurities such as arsenic are doped is formed on a semiconductor substrate, and a nitride film is formed in regions where p type pockets are formed on the both sides of a gate electrode. By implementing heat treatment in the atmosphere of oxygen, the portion below the nitride film is placed in the condition where it is equivalent when heat treated in the atmosphere of nitrogen whereby a p type impurity region and an n - type impurity region are formed. The region except for that below the nitride film is heat treated in the atmosphere of oxygen to form an n + type impurity region. Further, with the gate electrode as a mask, n - type impurity region and p type impurity region are formed, thereafter selectively growing a film on the side walls of the gate electrode to form an n + type impurity region with the gate electrode and the film as masks, thus producing a MOS transistor.

The characterization of doped iron oxide electrodes for the photodissociation of water: stability, optical, and electronic properties

Abstract: A characterization of optical and electronic properties is presented for p-type (Mg-doped) and n-type (Si-doped) iron oxides used in the photoelectrolysis of water. Photocurrent vs. wavelength spectra for these electrodes indicate that ..cap alpha..-Fe/sub 2/O/sub 3/ is the active optical component for both p-type and n-type materials. Band-edge locations for p-type and n-type iron oxides in sodium hydroxide aqueous solution are determined from differential capacitance measurements. The thermodynamic feasibility of the catalytic photodissociation of water without external potential is demonstrated for a short-circuited p/n diode assembly on an energy level diagram of the electrode/electrolyte interfaces. The open-circuit voltage (V/sub oc/) and short-circuit current (I/sub sc/) generated by the p/n assembly as a function of the intensity of laser irradiation indicate that these doped iron oxides are low mobility, high carrier density semiconductors. Photo-oxidation of water at the n-type anode is verified through oxygen detection. Gas evolution is monitored from an operating diode assembly using mass spectrometry and isotopically labeled water (H/sub 2//sup 18/O). Photocurrent from these p/n assemblies show excellent long-term stability in aqueous solution and Auger analysis of the semiconductor surfaces indicates no evidence of electrode dissolution.

NTD germanium: A novel material for low-temperature bolometers

Abstract: Six samples of ultra-pure (|NA − ND| ≤ 1011 cm-3), single-crystal germanium have been neutron transmutation doped to p-type with neutron doses between 7.5 × 1016 and 1.88 × 1018 cm-2. After thermal annealing at 400°C for six hours in a pure argon atmosphere, the samples were characterized with Hall effect and resistivity measurements between 300 and 0.3 K. The results show that the resistivity in the low temperature, hopping conduction regime can be approximated by ρ = ρoexp(Δ/T). The three more heavily-doped samples show values for ρo and Δ ranging from 430 to 3.3 Ω cm and from 4.9 to 2.8 K respectively. The excellent reproducibility of neutron transmutation doping and the values of ρo and Δ make NTD germanium a prime candidate for the fabrication of low-temperature, low-noise bolometers. The large variation in the tabulated values of the termal neutron cross sections for the different germanium isotopes makes it clear that accurate measurements of these cross sections for well defined neutron energy spectra would be highly desirable.

Optical and Electrical Properties of Electrochemically Doped n- and p-Type Polythiophenes

Abstract: Absorption spectra have been measured on polythiophene films subjected to electrochemical Bu4N+ doping The spectra show essentially the same evolution as those for BF-4 doping, ie, peaks at 06~07 eV and 15~18 eV appear upon doping in addition to the band-to-band absorption peak at 26 eV Propagation velocities of electrochemical doping of Bu4N+ and BF-4 along polythiophene films were estimated to be on the order of 10-3 cm/sec

Donor Levels in Si-Doped AlGaAs Grown by MBE

Abstract: Donor levels of MBE-grown Si-doped AlxGa1-xAs have been characterized by a combination of the C-V method and capacitance and current transient spectroscopy. Although most electrons are supplied by so-called DX centers in the AlAs mole fraction (x) range of 0.3~0.7 in this material, it is found that a small amount of shallow donors are still present. The concentrations of the DX center and the shallow donor are determined in detail as a function of AlAs mole fraction and Si doping level. The activation energy obtained by the Hall effect measurement is discussed in association with these data.

Hot electrons in modulation-doped GaAs-AlGaAs heterostructures

Abstract: We have investigated electric field heating of high mobility electrons in modulation‐doped GaAs‐AlGaAs heterostructures by simultaneous measurement of luminescence and mobility. We find that hot electrons have a Fermi‐Dirac distribution function for fields up to 750 V/cm and that the high field mobility of electrons can be understood in terms of field‐induced electron heating and the temperature dependence of low field mobility.