Electrical characterization of heavily doped polycrystalline silicon for high-frequency bipolar transistor application

Electrical conduction data from heavily doped p-type polysilicon thin films at room temperature and above are presented. Specifically, the sheet resistance, in the range from 1 kΩ/□ to 100 Ω/□ for a doping level of 10¹⁹cm^-3to 10²⁰cm^-3, is characterized over temperatures from 300 to 450 K. It is shown that the polysilicon resistivity, larger than the corresponding crystalline value by a factor ∼ 10, is flat over the entire temperature range used for measurement. This large resistivity is correlated to the degree of dopant activation and the mobility in polysiUcon. The measured mobility varying from 8 to 20 cm²/V . s is shown to be smaller than the crystalline mobility at the same doping level by a factor 7 ∼ 3. These data are comprehensively discussed and quantified, based on a distributed resistivity model.     

Activation of silicon ion-implanted gallium nitride by furnace annealing

Ion implantation into III–V nitride materials is animportant technology for high-power and high-temperature digital and monolithic microwave integrated circuits. We report the results of the electrical, optical, and surface morphology of Si ion-implanted GaN films using furnace annealing. We demonstrate high sheet-carrier densities for relatively low-dose (n_atoms=5×10¹⁴ cm⁻²) Si implants into AlN/GaN/sapphire heteroepitaxial films. The samples that were annealed at 1150°C in N₂ for 5 min exhibited a smooth surface morphology and a sheet electron concentration n_s ∼9.0×10¹³ cm⁻², corresponding to an estimated 19% electrical activation and a 38% Si donor activation in GaN films grown on sapphire substrates. Variable-temperature Hall-effect measurem entsindicate a Si donor ionization energy ∼15 meV.     

Sodium distribution in thermal oxide on silicon by radiochemical and MOS analysis

Direct comparison has been made between Na distribution determined radiochemically and electrically in 6000 Å thermal oxide on 10Ω-cm n-type Si. Na withinsiml 1000Å of Si/SiO2interface correlates in most cases with MOS flat band voltage shift, i.e. NNa(siml 1000Å) ≈ +ΔQMOS. Appreciable Na, which does not appear to affect Si surface potential, is found through the bulk of the oxide. Neutron activation of "clean" oxide (grown in wet or dry oxygen) showed ∼1 ppm Na throughout, ∼10 ppm at free surface. Gold was also identified at ppm concentrations but did not correlate with ΔQMOS. The U-shaped profile seen after diffusion (300 to 1000°C in dry N2) or in-drift (∼200°C, 5 × 10⁵V/cm) is believed due to rate limitation at the free surface; electrostatic binding plus enhanced solubility at the Si/SiO2interface. Time dependence was observed in diffusion at 500 and 800°C, which is not expected from the fast diffusion of Na. This is also attributed to the surface rate limitation. The anion significantly affects Na diffusion kinetics and distribution in contamination experiments with radiotracer Na²⁴OH, Na²⁴Cl, and Na²⁴Br⁸². Br is found to accompany Na diffusion, suggesting anion neutralization of Na within the bulk oxide. P2O5. SiO2is seen to "getter" Na from the oxide. These results support the suggestion of Snow et al. that Na is responsible for uncontrolled drift of surface potential in oxidized Si devices.     

Electronic properties of the silicon-thermally grown tantalum oxide interface

MOS capacitance measurements showed that the Si-Ta2O5interface prepared by thermal oxidation at ∼530°C of vacuum deposited Ta film followed by a heat treatment at 350°C in N2-H2is characterized by a negative "oxide" charge (6 × 10¹¹e/cm^-2at flat-band) and by an interface state density of ∼ 1 × 10¹²cm^-2(eV)^-1. The room temperature instability is small. The breakdown strength is >8 × 10⁶V/cm.     

Computation of electron and hole quasi-Fermi levels in polycrystalline silicon films under uniform illumination and zero bias

Numerical computation of quasi-Fermi levels (QFL) is carried out in a polycrystalline silicon film under uniform illumination and zero bias. This analysis is based on a single trap level at the grain boundary (GB) and Shockley-Read-Hall recombination kinetics. Mobility values, approximately one tenth those of the bulk values, are used, and they are assumed to be constant throughout the entire grain-GB region. Results show that considerable bending of the QFL occurs in the vicinity of the GB, and this bending δ is dependent both upon illumination levels as well as on grain size. The maximum bending, δp∼ 2.5 kT/q for majority-carrier QFL and δn∼ - 10 kT/q for minority-carrier QFL, is found for a grain size of ∼-0.33 µm and a doping of 2.9 × 10¹⁶cm^-3. The GB diffusion potential Vbdecreases by as much as 14 kT/q with illumination for large grains; but, for grains smaller than ∼0.2 µm, vbis insensitive to illumination up to 5 suns.     

High-speed current limiters

Current limiters based on the high-field saturation of electron-drift velocity in germanium have been fabricated by making two closely spaced ohmic contacts to a surface n-layer diffused into Ge. In operation, current flows from contact to contact through the n-layer. Current saturation begins at a voltageV_{s} = E_{s} d, where d is the contact spacing and Esis the field for saturation of electron drift velocity. Generally, in order to work at reasonable signal levels (volts and milliamperes) a structure small in all dimensions is required. A diffused-layer structure provides a convenient way of meeting this requirement and, at the same time, has, first, a high surface-to-volume ratio which facilitates heat removal and, second, a p-n junction which minimizes conductivity modulation by removing avalanche-generated holes. Limiters withd cong 2µ, and 10 µ × 10 µ contacts, were fabricated on Sb-diffused layers of 10³-Ω sheet resistance and ∼10¹⁷cm^-3surface concentration. Limiting current was ∼2.5 mA and limiting extended from ∼2 to 16 V. The conductance in the limiting range was ∼40 µmho and a contact-to-contact capacitance was ∼0.1 pF.     

InGaPAs-InP double-heterojunction high-radiance LED's

InGaPAs-InP double-heterojunction (DH) high-radiance LED's (λ ∼ 1.05-1.3 µm) have been fabricated by liquid-phase epitaxy (LPE) at constant temperature. The crystal growth procedure is described and the influence of InP substrate crystalline perfection is discussed. LED's with a high-radiance geometry suitable for coupling to an optical fiber have been fabricated. The four-layer double-heterostructure LED's have low forward-biased resistances. Typical external quantum efficiencies of ∼1.5 percent and narrow emission linewidths (∼56 nm, typical), have been measured for LED's (λ ∼ 1.08 µm) with an InGaPAs active layer thickness of 1.6 µm and an active layer carrier concentration ofN_{A} - N_{D} approx 2.8 \× 10^{16}cm^-3. The dependence of LED emission linewidth upon active layer doping is reported. Transient measurements show that the LED rise time is dependent upon current density for high-injection conditions. Preliminary lifetest results demonstrate only slight LED degradation after operation at 50 and 70°C for times up to ∼3500 h.     

Surface state and surface recombination velocity characteristics of Si-SiO2interfaces

A new device has been used to study the surface recombination velocity and surface state characteristics of Si-SiO2interfaces. The device consists of an epitaxially-formed junction diode. When the junction is forward-biased, minority carriers are injected from the heavily-doped substrate into the lightly-doped epitaxial region. The thickness of the epitaxial region is much less than the diffusion length for minority carriers. Thus, the diode current for a given junction forward bias is directly proportional to surface recombination velocity at the Si-SioO2interface. A gate electrode over the SiO2has been included to vary surface potential. Thus, this new device permits one to simultaneously study MOS capacitance-voltage characteristics as well as surface recombination velocity. The capacitance-voltage characterics indicate the surface states exhibit a quasi-continuous energy distribution. N-type surfaces exhibited donor levels lying in the range of ∼0.15 to ∼0.45 eV above the valence band; their density was found to vary from ∼5 × 10¹²to 5 × 10¹³states/cm²/eV. In contrast, p-type surfaces exhibited acceptor levels lying in the range of ∼0.15 to ∼0.45 eV below the conduction band; their density was comparable to those observed on n-type surfaces. The maximum value of surface recombination velocity was found to vary from 3 × 10³to > 10⁴cm/s. Surface recombination velocity was found to correlate directly with surface state density.     

P-type doping of GaAs by carbon implantation

The electrical properties of C-implanted <100> GaAs have been studied following rapid thermal annealing at temperatures in the range from 750 to 950°C. This includes dopant profiling using differential Hall measurements. The maximum p-type activation efficiency was found to be a function of C-dose and annealing temperature, with the optimum annealing temperature varying from 900°C for C doses of 5 × 10¹³ cm⁻² to 800°C for doses ≥5 × 10¹⁴cm⁻². For low dose implants, the net p-type activation efficiency was as high as 75%; while for the highest dose implants, it dropped to as low as 0.5%. Moreover, for these high-dose samples, 5 × 10¹⁵ cm⁻², the activation efficiency was found to decrease with increasing annealing temperature, for temperatures above ∼800°C, and the net hole concentration fell below that of samples implanted to lower doses. This issue is discussed in terms of the amphoteric doping behavior of C in GaAs. Hole mobilities showed little dependence on annealing temperature but decreased with increasing implant dose, ranging from ∼100 cm²/V·s for low dose implants, to ∼65 cm²/V·s for high dose samples. These mobility values are the same or higher than those for Be-, Zn-, or Cd-implanted GaAs.     

Generation of extreme ultraviolet radiation at 79 nm by sum frequency mixing

High brightness tunable coherent extreme ultraviolet (XUV) radiation at 79 nm with a peak power of ∼200 mW has been generated in H2gas by sum frequency mixing of two quanta from a high spectral brightness ArF* (193 nm) source with one quantum from a tunable dye laser (∼436 nm). Spectroscopic application of this radiation has been demonstrated by observation of a broad (∼160 cm^-1) autoionizing structure in Ar and narrow (∼2 cm^-1) autoionizing features in D2. An analysis is given which identifies the dominant molecular states involved in the nonlinear susceptibility of the medium (H2). The frequency independent tuning behavior of the 79 nm output power observed over ∼300 cm^-1is related to the molecular structure and response of the nonlinear medium in the intense optical field.     

ZnO spintronics and nanowire devices

ZnO is a very promising material for spintronics applications, with many groups reporting room-temperature ferromagnetism in films doped with transition metals during growth or by ion implantation. In films doped with Mn during pulsed laser deposition (PLD), we find an inverse correlation between magnetization and electron density as controlled by Sn-doping. The saturation magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature, suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn and factors such as crystalline quality and residual defects play a role. Plausible mechanisms for ferromagnetism include the bound magnetic polaron model or exchange that is mediated by carriers in a spin-split impurity band derived from extended donor orbitals. The progress in ZnO nanowires is also reviewed. The large surface area of nanorods makes them attractive for gas and chemical sensing, and the ability to control their nucleation sites makes them candidates for microlasers or memory arrays. Single ZnO nanowire depletion-mode metal-oxide semiconductor field effect transistors exhibit good saturation behavior, threshold voltage of ∼−3 V, and a maximum transconductance of 0.3 mS/mm. Under ultraviolet (UV) illumination, the drain-source current increased by approximately a factor of 5 and the maximum transconductance was ∼5 mS/mm. The channel mobility is estimated to be ∼3 cm²/Vss, comparable to that for thin film ZnO enhancement mode metal-oxide semiconductor field effect transistors (MOSFETs), and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination. The Pt Schottky diodes exhibit excellent ideality factors of 1.1 at 25°C, very low reverse currents, and a strong photoresponse, with only a minor component with long decay times thought to originate from surface states. In the temperature range from 25°C to 150°C, the resistivity of nanorods treated in H₂ at 400°C prior to measurement showed an activation energy of 0.089 eV and was insensitive to ambient used. By contrast, the conductivity of nanorods not treated in H₂ was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors. Sensitive pH sensors using single ZnO nanowires have also been fabricated.     

Ultrasmall superconducting tunnel junctions

Extremely small-area superconducting Josephson junctions have been fabricated using a newly developed electron-beam lithography technique. The junctions are composed of Pb-In base electrodes and Pb counter electrodes. Areas of the junctions range from 1 to 3 × 10^-10cm². The estimated capacitance is ∼10^-15F. Junctions have been produced with resistances of ∼100 Ω which have ∼20-percent hysteresis in the critical current at a temperature of 4 K.     

Pulse annealing of implanted InP with minimal phosphorus loss

Electron pulse annealing has been used to activate implanted layers in InP without the phosphorus loss dominance in earlier work. Reduced pulse energies were employed at which the phosphorus loss could be curtailed but which necessitated supplemental thermal heating of the substrate for activation. Relatively shallow implants (75 keV, 4 × 10¹⁴Si+cm^-2) so annealed show minimum yields of ∼ 5% from backscattering and are doped to over 10¹⁹cm^-3with mobilities of 500 cm²V^-1sec^-1.     

The correlation between stress relaxation and steady-state creep of eutectic Sn-Pb

This paper surveys and compares creep and stress relaxation data on finegrained eutectic Sn-Pb. It examines the consistency of the available data on this extensively studied solder material and studies whether stress relaxation offers a reasonable alternative to the more laborious conventional creep tests. The data survey reveals systematic differences between the creep behavior of material that is grain-refined by cold work and recrystallization (“recrystallized”) and that refined by rapid solidification (“quenched”). The recrystallized material has the conventional three regimes of creep behavior: a high-stress region with a stress exponent, n ∼ 4–7 and an activation energy Q ∼ 80 kJ/mole (a bit below that for self-diffusion of Pb and Sn), an intermediate region with n ∼ 2 and Q ∼ 45 kJ/mole (near that for grain boundary diffusion), and a low-stress region with n ∼ 3 and Q ∼ 80 (suggesting a reversion to a bulk mechanism). The quenched material shows only two regions: a high-stress creep with a stress exponent, n ∼ 3–7, and a low-stress region with n ∼ 3. The mechanisms in both regimes have activation energies intermediate between bulk and interface values (50–70 kJ/mole). With minor exceptions, the stress relaxation data and the creep data are in reasonable agreement. Most of the exceptions seem to be related to the difficulty of capturing the full details of grain boundary creep in stress relaxation tests.     

High strength in a long length for fibers coated at a speed of 5 m/s

We report the first results of high-strength fibers in long lengths (>5 km) coated at a speed of 5 m/s. A total length of 50.8 km of fiber in sample lengths ranging from ∼ 5 to ∼ 7 km was prooftested at three different stress levels up to 2.1 GN/m². It is found that the average survival length at two prooftest levels of 1.4 GN/m²(200 kg/in²) and 2.1 GN/m²(300 kg/in²) are, respectively, ∼10 and 3 km.     

Mo- and Ti-silicided low-resistance shallow junctions formed using the ion implantation through metal technique

Mo-and Ti-silicided junctions were formed using the ITM technique, which consists of ion implantation through metal (ITM) to induce metal-Si interface mixing and subsequent thermal annealing. Double ion implantation, using nondopant ions (Si or Ar) implantation for the metal-Si interface mixing and dopant ion (As or B) implantation for doping, has resulted in ultrashallow ( ≤ 0.1-µm) p⁺-n or n⁺-p junctions with ∼30-Ω sheet resistance for Mo-silicided junctions and ∼5.5-Ω sheet resistance for Ti-silicided junctions. The leakage current levels for the Mo-silicided n⁺-p junctions (0.1-µm junction depth) and the Mo-silicided p⁺-n junction (0.16-µm junction depth) are comparable to that for unsilicided n⁺-p junction with greater junction depth ( ∼0.25 µm).     

InP MISFET's with plasma anodic Al2O3and interlayed native Oxide gate insulators

InP MISFET's, with native oxide film interlayed between plasma anodic Al2O3film and the InP substrate, has been fabricated and showed the instability of the drain current reduced less than ± 4 percent for the period of 5 µs ∼ 5 × 10⁴s. The effective electron mobility is 2100 ∼ 2600 cm²/V.s at room temperature. The CV characteristics of MIS diodes and AES in-depth profiles are also discussed with respect to effects of interlaying native oxide film on device characteristics.     

1.3 µm LPE- and VPE-grown InGaAsP edge-emitting LED́s

Comparably high performance has been obtained from both vapor-phase and liquid-phase epitaxy InGaAsP/InP 1.3 μm edge-emitting LED's. Best results include 135 μW of optical power coupled into a 50 μm core 0.2 NA graded-index fiber, spectral half-widths ∼600 Å, rise/fall times ∼2 ns, ac modulation rates ∼200 MHz, and reliable operation in excess of 17 000 h @70°C and 3000 h @120°C. Asymmetries in the far-field patterns of these devices are also discussed.     

High-resolution low-level Brillouin spectroscopy in solids

In this paper some of the experimental considerations for obtaining phonon attenuation in solids by Brillouin scattering are described. Measurements of room temperature damping of longitudinal hypersonic waves in α-quartz, fused silica, and calcium fluoride are reported. The observed phonon frequency and linewidth for backward scattering of 6328-Å light in these solids is typically ∼ 30 GHz and ∼ 30 MHz (FWHM), respectively. This corresponds to a damping length ofsim 60 mu, which is inaccessible by conventional ultrasonics techniques.     

Zn-Implanted GaAs with minimized annealing redistribution

Redistribution associated with the annealing of high-dose Zn implants has been investigated in GaAs. Annealing times as short as ∼ 1 s have been implemented through direct radiant heating from an incoherent light source. It is shown that Zn can redistribute to depths of ∼ 1 µm even on annealing for only 10 s. Shallower layers (∼ 0.25 µm) and close to anticipated As-implanted depths require a further reduction in the annealing time to ∼ 1 s.