Nontrivial capacitance behavior, including a negative capacitance (NC)
effect, observed in a variety of semiconductor devices, is discussed
emphasizing the physical mechanism and the theoretical interpretation of
experimental data. The correct interpretation of NC can be based on the
analysis of the time-domain transient current in response to a small voltage
step or impulse, involving a self-consistent treatment of all relevant physical
effects (carrier transport, injection, recharging etc.). NC appears in the case
of the non-monotonic or positive-valued behavior of the time-derivative of the
transient current in response to a small voltage step. The time-domain
transient current approach is illustrated by simulation results and
experimental studies of quantum well infrared photodetectors (QWIPs). The NC
effect in QWIPs has been predicted theoretically and confirmed experimentally.
The huge NC phenomenon in QWIPs is due to the non-equilibrium transient
injection from the emitter caused by the properties of the injection barrier
and the inertia of the QW recharging.Comment: 9 pages, Latex, 11 ps figures; to be published in IEEE Trans. on
Electron Device
Avoiding cryogenic cooling not only reduces the cost and weight but also simplifies the infrared detector system allowing widespread usage. Here an uncooled infrared detection using intravalence bands is reported. A set of three p-GaAs/ Al x Ga 1−x As multiple heterojunction detector structures were used to demonstrate the concept experimentally. A preliminary detector showed peak responsivity of 0.29 mA/ W at 2.5 m at 300 K. The intravalence band approach can be used to cover various wavelength ranges by using different material systems giving rise to the possibilities of a dual band detector operating in atmospheric windows.
A heterojunction interfacial work function internal photoemission ͑HEIWIP͒ detector with a threshold frequency ͑f 0 ͒ of 2.3 THz ͑ 0 = 128 m͒ is demonstrated. The threshold limit of ϳ3.3 THz ͑92 µm͒ due to the Al fraction being limited to ϳ0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0 kV/ cm are 7.3 A / W, 29%, 5.3ϫ 10 11 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60°field of view was observed for a bias field of 0.15 kV/ cm. The f 0 could be further reduced toward ϳ1 THz regime ͑ϳ300 m͒ by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.
Hole transitions from the heavy-hole ͑hh͒ to the light-hole ͑lh͒ band contributing to the 4-10 m response range are reported on p-GaAs/ AlGaAs detectors. The detectors show a spectral response up to 16.5 m, operating up to a temperature of 330 K where the lh-hh response is superimposed on the free-carrier response. Two characteristic peaks observed between 5-7 m are in good agreement with corresponding energy separations of the lh and hh bands and thus originated from lh-hh transitions. Results will be useful for designing multi-spectral detection which could be realized on a single p-GaAs structure.
Heterojunction interfacial work function internal photoemission (HEIWIP) detectors provide an interesting approach to the development of quantum detectors for the terahertz range. In this letter, the cutoff frequency/wavelength variation of HEIWIP detectors having different Al fractions in AlGaAs/GaAs structures is experimentally verified, and a model is presented for designing the structures. A key feature of HEIWIP responsivity is the ability to cover a broad frequency range in a single detector with cutoff tailorability by adjusting the Al fraction in the barrier regions. Extending the response to lower frequencies by the use of AlGaAs emitters and GaAs barriers is also discussed.
High-quality 800-Å-thick films of tin-doped indium oxide have been prepared by magnetron sputtering. It is shown that films with low resistivity (∼4×10−4 Ω cm) and high optical transmission (≳85% between 4000 and 8000 Å) can be prepared on low-temperature (40–180 °C) substrates with O2 partial pressures of (2–7)×10−5 Torr.
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