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146 What mesoscopic structures really "remember": insufficiency of the open boundary approximation
Author(s): I. Knezevic, D. Ferry (Affiliation: Dept. of Electr. Eng., Arizona State Univ., Tempe, AZ, USA)
Conference: Sixth International Conference on New Phenomena in Mesoscopic Structures & Fourth International Conference on Surfaces and Interfaces of Mesoscopic Devices, Maui, HI, USA
Conference Date: 1-5 Dec. 2003
Journal: Superlattices Microstruct. (UK), vol.34, no.3-6, p.367-70 (Sept.-Dec. 2003)
Publisher: Academic Press, UK
Language: English
ISSN: 0749-6036, Full text
Document type: Conference paper in journal
Abstract: We analyze the influence of contact electrons onquantum transport in a resonant-tunneling diode (RTD), usinga many-body density matrix formalism for open systems. Weexplicitly relate the net current in the RTD to the memorycontainingeffective interaction between the RTD active regionand the contacts. This effect can only be captured if the RTDactive region is treated fully as a dynamically open system (5 refs.)
Inspec No.: 8249789
147 High-voltage operation with high current gain of pnp AlGaN/GaN heterojunction bipolar transistors with thin n-type GaN base
Author(s): K. Kumakura, T. Makimoto (Affiliation: NTT Basic Res. Labs., NTT Corp., Kanagawa, Japan)
Journal: Appl. Phys. Lett. (USA), vol.86, no.2, p.23506-1-3 (10 Jan. 2005)
Publisher: AIP, USA
Language: English
ISSN: 0003-6951, Full text
Document type: Journal article
Abstract: A pnp AlGaN/GaN heterojunction bipolar transistor(HBT) with a thin n-GaN base shows high-voltage operationwith high current gain in the common-emitter configuration atroom temperature. The device structure was grown bymetalorganic vapor phase epitaxy on a sapphire substrate.The emitter area is 30 ìm×50 ìm. The HBT can operate athigh voltage of 70 V with the maximum current gain of 40 atthe collector current of 10 mA. The maximum output powerdensity is 172 kW/cm2. Transport characteristics in the HBTwere also investigated. At small collector current, the currentgain is dominated by the recombination current at the emitterbaseheterojunction. At moderate collector current, thecalculated minority hole diffusion length well agreed with thatdetermined from electron beam induced currentmeasurements, indicating the current gain is dominated by theminority carrier diffusion. At large collector current, a highinjection effect was observed in the current gaincharacteristics (13 refs.)
Inspec No.: 8247226
148 Analysis and design of the dual-gate inversion layer emitter transistor
Author(s): N.K. Udugampola, R.A. McMahon, F. Udrea, G.A.J. Amaratunga (Affiliation: Dept. of Eng., Cambridge Univ., UK)
Journal: IEEE Trans. Electron Devices (USA), vol.52, no.1, p.99-105 (Jan. 2005)
Publisher: IEEE, USA
Language: English
ISSN: 0018-9383, Full text
Document type: Journal article
Abstract: The dual-gate inversion layer emitter transistor(DGILET) is a device in which the injection of minority carrierstakes place from an inversion layer formed under a MOS gate.Therefore, the device can be switched between MOS andbipolar modes using the gate giving the means to achieve asuperior combination of low conduction losses and lowswitching losses. The structure of the device and operation inboth the unipolar and bipolar modes are described in detail.Devices have been fabricated on bulk silicon wafers usingjunction isolation and experimental results confirm theexpected superior performance. In particular, the resultsconfirm predictions that if the inversion layer injector isproperly designed, the voltage snapback that occurs duringthe transition between unipolar and bipolar modes can becompletely suppressed. This can be achieved with a compactstructure in contrast to the extended structures required inanode-shorted lateral insulated gate bipolar transistor(LIGBTs). An equivalent circuit for the DGILET is presentedand the control of the minority carrier injection is alsoanalyzed. Experimental results show that the DGILET canswitch at speeds approaching those characteristic ofMOSFETs with operating current densities comparable toLIGBTs. The results show that the DGILET offers lower overalllosses than an LIGBT at switching frequencies above about10 kHz (12 refs.)
Inspec No.: 8249849
149 An analysis of base bias current effect on SiGe HBTs
Author(s): Yo-Sheng Lin (Affiliation: Dept. of Electr. Eng., Nat. Chi-Nan Univ., Puli, Taiwan), Shey-Shi Lu
Journal: IEEE Trans. Electron Devices (USA), vol.52, no.1, p.132-6 (Jan. 2005)
Publisher: IEEE, USA
Language: English
ISSN: 0018-9383, Full text
Document type: Journal article
Abstract: The anomalous dip in scattering parameter S11 ofSiGe heterojunction bipolar transistors (HBTs) is explainedquantitatively for the first time. Our results show that for SiGeHBTs, the input impedance can be represented by a "shifted"series RC circuit at low frequencies and a "shifted" parallel RCcircuit at high frequencies very accurately. The appearance ofthe anomalous dip of S11 in a Smith chart is caused by thisinherent ambivalent characteristic of the input impedance. Inaddition, it is found that under constant collector-emittervoltage (VCE), an increase of base current (which correspondsto a decrease of base-emitter resistance (rð ) and an increaseof transconductance (gm)) enhances the anomalous dip, whichcan be explained by our proposed theory (13 refs.)
Inspec No.: 8249857
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