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I. INTRODUCTIONers in these devices is monitored by means of a semiclassicaltwo-dimensional~2D!ensemble MC simulator in which bothInAlAs/InGaAs high electron mobility transistors impact ionization and hole recombination are included. This~HEMTs!have proven a record of excellent performance for approach allows one to determine the origin and magnitudelow-noise high-frequency applications~in microwave and of the kink effect in terms of internal quantities~like electronmillimeter-wave frequency ranges!, and are used as active and hole co anddevices in high-speed integrated circuits.1±3However,theycompletephnycseinctarlatiuonndserstandpiontgentoifaltphreo®kliens!k,seofftehctatiashave still some drawbacks to be eliminated, like the kink achieved, thus providing some guidelines to be followed ineffect, i.e., an anomalous increase in the drain currentIDat the fabrication process of HEMTs in order to improve theirsuf®ciently high drain-to-source voltagesVDS, which leads immunity to kink effect.to a reduction in the gain and a rise in the level of noise, thus The article is organized as follows. In Sec. II, the physi-limiting the utility of these devices for microwave power cal model is detailed. The main results of our simulations4applications. and their discussion are provided in Sec. III. Finally, in Sec.When reducing the device dimensions to improve the IV, we draw the most important conclusions of this work.frequency range of operation of HEMTs, very high electric®elds appear in the gate±drain region of the device, which,jointly with the narrow band gap of InGaAs, makes this de-II. PHYSICAL MODELvice very susceptible to impact ionization mechanisms.1As mentioned b e r the calc seSomeworkssuggestthatimpactionizationandthesubse-ofanensembleMCesfiomru,laftoorself-conuslisattieonnts,wemakeuquent hole dynamics~jointly with trapping processes!canbea2DPoissonsolverwhichincorporatesalltlhyecporuopcleesdsewsitahtresponsible for the kink effect.4±10However, kink phenom- the origin of the kink effect. The structure under analysis is aena are not still completely understood, specially in short-channel HEMTs.4100 nm T-gate recessed HEMT~Fig. 1!, and consists of a InPsubstrate~not simulated!, a 200 nm In0.52Al0 48As buffer fol-Thus, the use of a microscopic approach beyond the.rsstandard drift-diffusion models typically employed to ana- lowed by a 25 nm thick In0.53Ga0.47Aschannel,threelayeedlyze this effect is highly desirable. The Monte Carlo~MC!loafyeIrn0.m52oAdle0l.e48dAass~aa55nnmmlasypearcedro,paed5a3t1N01D25c1m02129,cmd-2d3opandmethod has been proven to be a very useful tool when deal-ing with problems where the understanding of the micro- a 10 nm Schottky layer!, and, ®nally, a 10 nm thickscopic behavior of carriers is essential.11±14TheaimofthisIetne0.r5s3fGoar0.e4l7eAcstrocnaspilnaytherei(nNvDol5ve5d3m1a0t1e8ricamls2c3)a.nTbehefopuanrdamin-work is the development of a physical model for the kink w le de ristics and noiseeffect in short-channel recessed In0.52Al0.48As/In0.53Ga0.47AsbReehf.av1i1o,rofhithisdteaviilcseoffotrhleoswtaatipcplciehdaravcotletages~in absenceHEMTs. Toward this end, the microscopic transport of carri- of impact ionization!can be found in Refs. 12 and 13, inwhich the agreement between the results of the simulationsa!Electronic mail: a50343@usal.esand the experimental measurements con®rm the validity of0021-8979/2003/94(6)/4096/6/$20.00 4096  2003 American Institute of Physics
JOURNAL OF APPLIED PHYSICS VOLUME 94, NUMBER 6 15 SEPTEMBER 2003Monte Carlo study of kink effect in short-channel InAlAsÕInGaAs highelectron mobility transistorsB. G. Vasallo,a)J.Mateos,D.Pardo,andT.GonzaÂlezDepartamentodeFõÂsicaAplicada,UniversidaddeSalamanca,PlazadelaMerceds/n,37008 Salamanca, Spain~Received 12 February 2003; accepted 25 June 2003!A semiclassical two-dimensional ensemble Monte Carlo simulator is used to perform a physicalmicroscopic analysis of the kink effect in short-channel InAlAs/InGaAs lattice-matched highelectron mobility transistors~HEMTs!. Due to the small band gap of InGaAs, these devices are verysusceptible to suffer impact ionization processes, with the subsequent hole transport in the channel,both supposedly implicated in the kink effect and easy to be implemented in a Monte Carlosimulation. The results indicate that for high enoughVDS, holes, generated by impact ionization,tend to pile up in the channel under the source side of the gate due to the attracting potential causedby the surface charge at the recess and, mostly, by the gate potential. Due to this pile up of positivecharge, the potential barrier controlling the current through the channel is lowered, so that thechannel is further opened andIDincreases, leading to the well known kink effect in the current±voltage characteristics. The microscopic understanding of this phenomenon provides valuableinformation to conceive the optimum fabrication process for kink-effect-free HEMTs. 2003American Institute of Physics.@DOI: 10.1063/1.1603955#
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