Topic
Biasing
About: Biasing is a research topic. Over the lifetime, 29422 publications have been published within this topic receiving 301035 citations.
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186 citations
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TL;DR: In this article, the 0.7 (2e^2/h) conductance anomaly is investigated in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as the temperature.
Abstract: The 0.7 (2e^2/h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as a function of temperature. We investigate in detail how, for a given gate voltage, the differential conductance depends on the finite bias voltage and find a so-called self-gating effect, which we correct for. The 0.7 anomaly at zero bias is found to evolve smoothly into a conductance plateau at 0.85 (2e^2/h) at finite bias. Varying the gate voltage the transition between the 1.0 and the 0.85 (2e^2/h) plateaus occurs for definite bias voltages, which defines a gate voltage dependent energy difference $\Delta$. This energy difference is compared with the activation temperature T_a extracted from the experimentally observed activated behavior of the 0.7 anomaly at low bias. We find \Delta = k_B T_a which lends support to the idea that the conductance anomaly is due to transmission through two conduction channels, of which the one with its subband edge \Delta below the chemical potential becomes thermally depopulated as the temperature is increased.
185 citations
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TL;DR: A pH sensor fabricated on a single chip by an unmodified, commercial 0.6-/spl mu/m CMOS process is presented in this article, which comprises a circuit for making differential measurements between an ion-sensitive field effect transistor (ISFET) and a reference FET (this articleET).
Abstract: A pH sensor fabricated on a single chip by an unmodified, commercial 0.6-/spl mu/m CMOS process is presented. The sensor comprises a circuit for making differential measurements between an ion-sensitive field-effect transistor (ISFET) and a reference FET (REFET). The ISFET has a floating-gate structure and uses the silicon nitride passivation layer as a pH-sensitive insulator. As fabricated, it has a large threshold voltage that is postulated to be caused by a trapped charge on the floating gate. Ultraviolet radiation and bulk-substrate biasing is used to permanently modify the threshold voltage so that the ISFET can be used in a battery-operated circuit. A novel post-processing method using a single layer of photoresist is used to define the sensing areas and to provide robust encapsulation for the chip. The complete circuit, operating from a single 3-V supply, provides an output voltage proportional to pH and can be powered down when not required.
185 citations
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01 Aug 1995
TL;DR: In this article, a two-dimensional (2D) vertical cavity surface emitting laser (VCSEL) structures have been grown by both metal-organic chemical vapour deposition (MOCVD) and molecular beam fabrication (MBE).
Abstract: Vertical cavity surface emitting laser (VCSEL) structures have been grown by
both metal-organic chemical vapour deposition (MOCVD) and molecular beam
epitaxy (MBE). These incorporate 3 strained InGaAs / GaAs quantum wells placed
resonantly in a two wavelength long optical cavity, formed between AlAs / GaAs
quarter wave dielectric reflector stacks through which current is injected.
The reflection spectra of these stacks is studied in detail; the effects on the
laser threshold gain of absorption due to impurities and of errors in growth are
investigated. Methods of disruption of the AlAs / GaAs heterointerfaces have been
used to reduce the operating voltage. The completed designs use 200A intermediate
layers containing 30 or 50% aluminium or a superlattice graded region simpler than
that used in previous designs. The effectiveness acceptor dopants; Be in MBE, C and
Zn in MOCVD; is studied also. Modulation doping was employed to reduce the
effects of optical absorption.
Devices were fabricated into mesas by SiC14 reactive ion etching or defined
by proton implant isolation. MBE grown devices were resonant at wavelengths in the
range 950 to 1059mn with essentially constant (at —1020nm) eihhi transition
energies in the wells. A detailed study of the wavelength variation of threshold
current density
Jth (X)was made. A minimum of 366A.cnr2 was measured at
1018nm in mesa devices. A similar relation is found for ion-implanted devices but the
minimum is increased to 535A.cm-2 by incomplete isolation. Gain calculations,
including strain effects, are used to explain the Jth(X) variation.
Implanted devices offer superior c.w. performance due to reduced thermal and
ohmic resistances. The relative offset between the gain spectrum and cavity resonance
was examined for c.w. operation. It was found that carrier thermal effects limit the
output power rather than shifts in the offset.
The bias voltage of MOCVD grown devices is as low as 1.7V and the
threshold current is as low as 764A.cm-2. This is higher than for MBE grown devices
because of growth thickness errors and non-optimal alignment of the gain spectrum
and cavity mode. The uniformity in emission wavelength is ±1% over 80% of a 2 inch
diameter wafer, offering suitability for very large uniform arrays.
184 citations
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17 May 2005TL;DR: In this article, a method of depositing a carbon layer on a workpiece includes placing the workpiece in a reactor chamber, introducing a carbon-containing process gas into the chamber, generating a reentrant toroidal RF plasma current in a path that includes a process zone overlying the work piece by coupling plasma RF source power to an external portion of the path, and coupling RF plasma bias power or bias voltage to the workpieces.
Abstract: A method of depositing a carbon layer on a workpiece includes placing the workpiece in a reactor chamber, introducing a carbon-containing process gas into the chamber, generating a reentrant toroidal RF plasma current in a reentrant path that includes a process zone overlying the workpiece by coupling plasma RF source power to an external portion of the reentrant path, and coupling RF plasma bias power or bias voltage to the workpiece.
182 citations