Minimum Carrier Research Articles

Optical and electrical properties of InN thin films grown on ZnO/α-Al2O3 by RF reactive magnetron sputtering

We have prepared indium nitride (InN) thin films on ZnO/α-Al2O3 by RF reactive magnetron sputtering and studied their optical and electrical properties using such analytical techniques as X-ray diffraction (XRD), van der Pauw technique, atomic force microscopy (AFM) and double-beam spectroscopy. ZnO-buffered α-Al2O3 is effective to the epitaxial growth of InN thin films and, furthermore, improve their electrical properties. ZnO buffer layers transmit the information on c-axis orientation from (0001) α-Al2O3 substrates to InN thin films, which grow epitaxially along lateral orientation because of less lattice mismatch between InN and ZnO than that between InN and α-Al2O3. The maximum Hall mobility is 60 cm2/V·s and the minimum carrier concentration is 2×1020 cm−3. From optical transmission spectra, optical constants of the films are obtained based on Kramers–Krönig analysis. The refractive index n is around 1.8 in the photon energy of 1.0–2.5 eV and the band gap is approx. 1.8 eV.

Temperature dependence of 1.55 μm VCSELs

The temperature for minimum threshold carrier concentration in 1.55 μm VCSELs can be significantly lower than that at which the peak gain matches the cavity resonance. A simple model is implemented to investigate the magnitude of this temperature difference and to aid the design of VCSELs for room temperature operation.

On-line atomization of selenium hydride in graphite furnaces: estimate of atomic absorption coefficient and spectroscopic temperature

A transversely heated graphite tube atomizer (THGA) has been employed to ensure constant temperature within the observation volume. A method of sampling of gaseous selenium hydride from a container has been developed including a relation between observed peak area (integrated absorbance) and selenium mass injected into the furnace. This makes it possible to control fully the composition of the atomizer atmosphere. A boron nitride tube sealed to the injection hole of the graphite tube has been used as the interface. It performed well even at the highest tested atomization temperature (2400°C). Spectroscopic temperature measurements based on atomic absorption at the 196.1 nm and 204.0 nm Se lines have been used to determine the influence of carrier gas flow rates on the effective gas phase temperature in the atomizer at set furnace temperatures of 1800°C and 2200°C. Characteristic masses m 0 at the 196.1 nm line, in pure argon atmosphere, have been determined at these set furnace temperatures for various argon gas flow rates. The data are employed to estimate an experimental value of the atomic absorption coefficient: (17.1 ± 0.8) × 10 −18 m 2. The value does not significantly differ from the theoretical value. m 0 values found for the temperature range 1800–2400°C for the hydride injection into the furnace at the minimum feasible carrier gas flow rate are compared with characteristic masses for the traditional liquid sampling to the furnace in the same temperature range. This made it possible to estimate that the analyte losses through the injection port in the case of the traditional liquid sampling to the furnace are in the range 20–25%.

Illumination-induced inhomogeneity in the carrier density profile of split gate devices

We demonstrate that low-temperature illumination of a GaAs/AlGaAs Hall bar, partially covered by a split metal gate structure, results in the formation of a shallow barrier across the entire device, even in the point contact openings not directly covered by the gates. The minimum carrier density inhomogeneity is determined from the position of the anomalous Hall steps, which are observed even at zero gate voltage as a result of barrier formation. Our results suggest a substantial contribution to the carrier density inhomogeneity, implying that low-temperature illumination may considerably increase disorder in split gate nanostructures.

Pressure-Controlled GaN MBE Growth Using a Hollow Anode Nitrogen Ion Source

ABSTRACTGaN films were grown on sapphire substrates at temperatures below 1000 K utilizing a Hollow Anode nitrogen ion source. A Ga flux limited growth rate of ~ 0.5 µm/h is demonstrated. Active utilization of strain and the assistance of a nitrogen partial pressure during buffer layer growth are found to be crucial issues that can improve the film quality. The best films exhibit a full width at half maximum of the x-ray rocking curves of 80 arcsec and 1.85 meV for the excitonic photoluminescence measured at 4 K. A Volmer-Weber three dimensional growth mode and the spontaneous formation of cubic GaN inclusions in the hexagonal matrix are observed in the investigated growth temperature range. It is argued that this growth mode contributes to a limitation of the carrier mobility in these films that did not exceed 120 cm2/Vs though a minimum carrier concentration of ~ 1015 cm−3 was achieved.

Implantation isolation in n-type InP bombarded with He + and B +

An extensive study has been carried out to investigate the changes in the electrical properties of n-type InP, doped in the range 2.5 × 10 16–1 × 10 18 cm −3, and bombarded with 55 keV He + and 125 keV B +. The carrier concentration initially decreases with ion dose and reaches a minimum at a dose of ∼ 5 × 10 13 cm −2 for He + and 1 × 10 13 cm −2 for B + irradiation. The dose where the minimum occurs for each ion and the magnitude of the minimum carrier concentration is independent of the initial carrier concentration. However, at doses below this minimum the carrier removal rate is directly dependant on the carrier concentration. At higher doses the electrical properties are dominated by radiation defects and are independent of initial doping. These results are discussed in terms of the production of defects and defect/dopant interactions.

Integrated power control and base station assignment

In cellular wireless communication systems, transmitted power is regulated to provide each user an acceptable connection while limiting the interference seen by other users. Previous work has focused on maximizing the minimum carrier to interference ratio (CIR) or attaining a common CIR over all radio links. However, previous work has assumed the assignment of mobiles to base stations is known and fixed. In this work, we integrate power control and base station assignment. In the context of a CDMA system, we consider the minimization of the total transmitted uplink power subject to maintaining an individual target CIR for each mobile. This minimization occurs over the set of power vectors and base station assignments. We show that this problem has special structure and identify synchronous and asynchronous distributed algorithms that find the optimal power vector and base station assignment. >

Effect of a Subanesthetic Minimum Alveolar Concentration of Isoflurane on Two Tests of the Hypoxic Ventilatory Response

These experiments were designed to study the effect of 0.1 minimum alveolar concentration isoflurane on the hypoxic ventilatory response as measured by two common methods of hypoxic testing: when normocapnic hypoxia was induced abruptly and when it was induced gradually. We hypothesized that any disparity in results would be due to an isoflurane effect that was manifested differently in the two tests. After 20 min for uptake and equilibration of 0.1 minimum alveolar concentration end-tidal isoflurane or carrier gas in hyperoxia, isocapnic hypoxia was induced either abruptly over 60-80 s ("step" test) or gradually over 10 min ("ramp" test), followed by 20 min of isocapnic hypoxia at 45 mmHg end-tidal oxygen. Control of the hypoxic and isocapnic stimuli was accomplished accurately by a computer-controlled dynamic end-tidal forcing system. Eight subjects performed each test in the presence and absence of isoflurane. For both step tests and ramp tests, 0.1 minimum alveolar concentration isoflurane had no effect on minute ventilation during the defined periods of hypoxia. With isoflurane, delta VE45, the acute change in ventilation from hyperoxia to hypoxia, was 97 +/- 20% (mean +/- SEM) of the control response for step tests and 100 +/- 25% of the control response for ramp tests. The step tests produced significantly larger acute hypoxic responses than did the ramp tests, but by the end of 20 min of hypoxia, ventilation was similar for both tests. Neither method of hypoxic testing demonstrated the level of isoflurane effect reported by others. A comparison of the two methods of hypoxic testing suggests that ramp tests, as commonly performed, do not allow adequate time for full expression of the acute hypoxic ventilatory response. Step tests also better separated the opposing hypoxic effects of carotid body stimulation and central ventilatory depression.

Single-pulse pump-probe measurement of optical nonlinear properties in GaAs/AlGaAs multiple quantum wells

Single-pulse ps-pump and ns-probe nonlinear transmission measurements provide carrier-density-dependent optical nonlinear spectra in GaAs/AlGaAs multiple quantum wells grown by metalorganic chemical vapor deposition. The use of the ps pump eliminates the need to know carrier lifetime to determine carrier density. The saturation behavior of changes in absorption coefficient and refractive index are modeled by a simple saturation equation to obtain saturation carrier density. The saturation spectra for different well thicknesses are obtained. The minimum saturation carrier density appears around 150 /spl Aring/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Constrained power control

High system capacities can be achieved by controlling the transmitter power in multiuser radio systems. Power control with no constraint on the maximum power level has been studied extensively in earlier work [1–18]. Transmitter power is at a premium in radio systems such as cellular systems and PCS. There is a limit on the maximum transmitter power especially at the terminals (e.g. mobile units and handsets) since the power comes from a battery. In this paper we study power control that maximizes the minimum carrier to interference ratio (CIR), with a constraint on the maximum power. The optimal power vector solution lies on the boundary of the constrained power vector set and achieves a balance in the CIR's. Results indicate that the constraints do not induce any stability problems. A distributed scheme with favourable convergence properties and close to optimum performance is presented. Simulation results show that the algorithm tries to maximize the number of terminals served with CIR greater than or equal to the target CIR, while conserving power.

Photoluminescence study of lateral carrier confinement and compositional intermixing in (Al,Ga)Sb lateral superlattices

We have compared the photoluminescence properties of an (Al,Ga)Sb lateral superlattice (LSL) quantum well to those of an (Al,Ga)Sb alloy quantum well, with respect to recombination energy and polarization dependence. From the results we have deduced the compositional intermixing and lateral carrier confinement present in the LSL structure. We found that the LSL well luminesces at 36 meV lower than the alloy well, and that emitted light from the LSL well is more than twice as intense when its electric field is polarized parallel versus perpendicular to the LSL ‘‘wires.’’ From these data we calculate that the lateral content of the LSL varies periodically between approximately 24% and 42% AlSb, and the maximum:minimum carrier density ratios are about 4:1 and 6:1 for electrons and heavy holes, respectively.

Formation of bacterial aggregates in a continuous-flow reactor: Influence of carrier availability

A dilution-rate shift-up was employed to induce bacterial hold-up in a continuous-flow gas-lift reactor. A minimum carrier concentration (sand, 2–5 g/l) was found a prerequisite for formation of bacterial aggregates, which fermented glucose either to propionate/acetate or to butyrate/acetate. Higher levels of sand did not affect the onset of propionate/acetate-forming aggregates, but decreased the rate at which they subsequently grew. Reversely, butyrate/acetate-producing aggregates grew at a constant rate but the onset of their formation was progressively retarded by increasing sand concentrations. In both cases, completion of start-up was most rapid at low sand concentrations.

High mobility polycrystalline SnTe:Ge films

High mobility polycrystalline SnTe:Ge films have been prepared by co-evaporation of tin and germanium from a single source in an atmosphere of tellurium vapour for different weight percentages of germanium. It has been found that SnTe:Ge films with germanium content around 0.8 weight percent have got maximum mobility (≈ 1150 cm 2V −1s −1 at room temperature) and minimum carrier concentration (∼ 3 × 10 19 cm −3 at room temperature).

Responses of single neurons in cat auditory cortex to time-varying stimuli: linear amplitude modulations.

Single neurons in the auditory cortex of anesthetized cats were examined quantitatively for their sensitivity to the sound pressure level of characteristic frequency (CF) tone pulses, and to 6 dB, linear modulations in the amplitude of a continuous CF carrier tone. The direction and rate of amplitude modulation (AM), and the carrier level on which it was imposed, were manipulated parametrically. Studied with amplitude modulations, the majority of neurons responded only to intensity increments. The minimum carrier level upon which an amplitude modulation was able to evoke spike discharges was typically comparable to the tone pulse threshold SPL. For many neurons, an "intensity increment response area", i.e., the domain of AM rate and carrier level conjunctions within which a 6 dB AM was able to evoke discharges, could be delimited. For many neurons, preferred rate of AM drifted from high to low with increases in the carrier level on which the modulation was imposed. The most vigorous responses to AM stimuli often occurred when the carrier levels were associated with the rising slope or the peak of the tone pulse rate intensity function. It may be possible to understand the general form of AM response areas in terms of short-term adaptation, the disposition of excitatory and inhibitory tone pulse response areas, and the spectra of the AM stimuli used.

Metalorganic growth of high-purity HgCdTe films

Epitaxial films of HgCdTe have been grown by metalorganic chemical vapor deposition. Diethyltelluride, dimethylcadmium, and elemental mercury were used as the starting reagents. For Hg1−xCdxTe compositions with x≤0.2, the films are n type at 300 and 77 K. From Hall measurements at 77 K a minimum carrier concentration of 1.0×1015 cm−3 and maximum mobility of 590 000 cm2/Vs were measured. Epitaxial films with x≊0.3 were also grown. The films are n type at 300 K but exhibit p-type behavior at 77 K. p-type carrier concentrations less than 5×1015 cm−3 were attained.

Carrier distribution and low-field resistance in short n+-n--n+and n+-p--n+structures

In the present paper, we calculate the potential, field, and carrier distributions in short n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> devices and estimate the low-field resistance. The results of the calculations present a set of universal curves which may be used to find the minimum carrier density in the sample, the barrier height, the electric field at the boundary, etc. Our calculations show that electron injection becomes very important when the doping level is smaller than 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> (cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ). (T/300 K)/ L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (µm) for GaAs diodes, where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> is the sample length. The low-field resistance of the sample is limited by the thermionic emission of the sample and by the diffusion and drift in the sample. The thermionic emission dominates at low temperatures, in short samples, and the diffusion-drift dominates in longer samples at higher temperatures. The experimental values of low-field resistance for GaAs 0.4-µm n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> devices at 77 and 300 K are in good agreement with the predicted values. The agreement is not so good for 0.25-µm devices and for n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> devices. In the latter case, the disagreement may be due to uncertainty in the doping level because the low-field resistance of the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> -n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> structure is shown to be very sensitive to the doping level of the p-region.

Incentive Contracting for Railroad Subsidies: A Statistical Approach to Cost Control

An optimal method of subsidy would necessarily entail methods of subsidy cost control. The purpose of this article is to develop and empirically evaluate the feasibility of such a method of control, which encourages subsidy cost limitation through performance incentives for subsidized carrier cost efficiency. Empirical findings suggest that a statistical approach to minimum necessary or target carrier cost estimation may make the suggested method of cost control applicable in a number of regulated sectors.

Determination of buried channel parameters from IV and CV measurements

A simple, direct method is described for the extraction of the minimum carrier potential vs charge packet size in a buried channel CCD. Also obtainable from this technique is a direct measurement of the location of the top of the charge packet with respect to the silicon surface. Close correlation is found between the results obtained from this technique and the predictions of the step junction depletion layer approximation.

Optical frequency translator of the minimum residual carrier

Optical frequency translator of the minimum residual carrier

THE DETERMINATION OF CALCIUM-45 IN SEA WATER, CORALS AND CALCAREOUS ALGAE BY LIQUID SCINTILLATION COUNTING

Summary Calcium isolated from various fractions of corals and algae is converted into nitrate and dissolved in a water-ethyleneglycolmonoethylether-dioxane cocktail in the ratio of 1:2:20 using PPO and 1-dimethyl-POPOP as scintillators. 45Ca in sea water is counted directly after dilution of 1:10 with water. The carrier capacity of the system is 3 mmole Ca (NO3)2/23 ml (120 mg Ca). The counting efficiencies at minimum and maximum carrier concentration are 88,7% and 78,5% respectively. The scintillator solvent system is chemically stable and counts are highly reproducible. Instagel in the ratio of 10 ml to 1 ml aqueous solution gives counting efficiencies in the region of 80%. Sea water can be incorporated directly. Algal calcium is counted as the nitrate or the chloride. The carrier capacity of Instagel is higher and the counting efficiency is less affected by large concentrations of carrier and excess acid.