InAs Inserted Channel HEMT MDCL 이 종 원

Contents I. Introduction II. The Design of Subchannel of InAs III. Normal VS Inverted HEMT IV. AlSb/InAs HEMT Growth on S.I. GaAs

Overview of InGaAs HEMT  Advantage for use in low noise and high frequency device  their high electron mobility & high sheet carrier density & high saturation drift velocity if the InAlAs/InGaAs 2DEG system  Conventional InP HEMT structure : high contact and gate electrode can cause large parasitic source and drain resistances (by the large conductance band discontinuity between the InGaAs cap layer and InAlAs layer, forming a barrier in the current flow between these layers)

I. Introduction  Why? I. Superior to GaAs or InGaAs channel devices a) their low-field mobility b) higher-lying satellite valleys c) deeper quantum well depth d) higher overshoot velocity II. Scaling Factor (for sub 0.1um device) a)As Lg decreases, an appropriate aspect ratio has to be maintained to alleviate short channel Effect. b)Also, Channel thickness has to be reduced for proper aspect ratio ( ∵ The thinning of barrier layer is limited by current tunneling) c)Disadvantage ( Reducing of sheet carrier density in a channel and Undesired scattering phenomena because of hetero-junction interface and the enhancement of ionized dopant in supply layer)

InAs Inserted Channel HEMT  Conventional InP HEMT vs InAs Inserted HEMT (Ref. 1) Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48As Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48As Barrier I In0.52Al0.48As Spacer i In0.52Al0.48As Channel i InxGa1-xAs Channel i InAs Buffer i In0.52Al0.48As InP Substrate Delta-doping Conventional InP HEMTInAs Inserted HEMT

Carrier Transport Characteristic  (Ref. 6) a) Modified Composite Channelb) Conventional InGaAs HEMT c) Conventional Composite chanel HEMT High Indium Composition Layer Mobility (cm2/Vs)Sheet Carrier density (cm-2) Carrier Confinement In0.8Ga0.2As/InAs/In0. 8Ga0.2As e1292% In0.8Ga0.2As e1274% InAs e1261%

Issue of the InAs Inserted HEMT I. The Design of Subchannel of InAs for composite channel (dependence of a) Temperature & Thickness b) Enhancement of carrier transport ) II. The Normal and Inverted HEMT Structure III. AlSb/InAs HEMT (The Growth on S.I GaAs )

Physics  The Basic Idea of Composite Channel  Low field channel region => electrons are mostly located in the high-mobility, small bandgap InGaAs layer  High field channel region => The energy of the electrons increases and more and more electrons populate the InP layer => Because of the larger bandgap, the rate of impact ionization in InP is smaller compared to that in the InGaAs channel => While the low-field mobility of InP is smaller than that of InGaAs, the high-field transport properties, especially the saturation velocity, are better in InP

Physics  Band Structure Calculation and Electron Transport (Ref.2)  Γ-valley mass of strained InAs (parallel<Perpendicular)  => The strain brings about an increase of the InAs band gap of 0.12eV InGaAs (x=0.53) Strained InAsInAs E(l-Γ) (eV) E(Γ-X)(eV) m＊(Γ)m＊(Γ) (//), 0.04( ㅗ ) ml ＊ (L) mt*(L) (t1) 0.091(t2) 0.12 ml ＊ (X) mt*(X) (t1) 0.150(t2) 0.28 α(Γ)(eV-1) α(Γ)(eV-1) α(Γ)(eV-1) a(A) (//)6.054

Physics  Monte Carlo Simulation  Include polar optical phonon scattering and inter-valley deformation potential scattering at 300K 26% enhancement 16% enhancement In0.53GA0.47AsUnstrained InAsStrained InAs Mobility (cm2/Vs) Peak Drift Velocity (m/s) 3.1e73.65e7 The reduction of slope Wide Γ-L band separation in InAs =L enhancement of electron heating Over 7kV/cm Electron energy of strained InAs> unstrained InAs => Smaller effective mass L & X valley of strained InAs => Higher energy

II. The Design of Subchannel (Ref.3) a) Mobility tested the function of Z and Lw b) This test’s result is Z=3nm and Lw=4nm (Consideration of Carrier Modulation and Short Channel Effect) => 13000cm2/Vs

II. The Design of Subchannel  The Thickness of InAs Inserted HEMT (Another Test) (Ref. 4)  Double Sided Delta-doping 을 이용 (for low output conductance and kink-free I/V Characteristic) a) The Enhancement of the electron transport property b) 47% electron mobility improvement 40% the effective electron velocity increment 300K)

II. The Design of Subchannel  Design Issue (Ref.5)  3.5% lattice mismatch of InAs on InP --- Structure A Structure B Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48As Cap n In0.53Ga0.47As n In0.53Ga0.47As/In0.52Al0.48As Barrier I In0.52Al0.48As Spacer i In0.52Al0.48As Channel i In0.53Ga0.47As Channel i InAs Buffer i In0.52Al0.48As InP Substrate Buffer i In0.52Al0.48As Channel i InAs Channel i In0.3Ga0.7AsChannel i In0.7Ga0.3As Channel i In0.53Ga0.47As Channel i In0.7Ga0.3AsChannel i In0.3Ga0.7As Compressively strained channel Structure A Tensilely strained channel Structure B 17% population increment 10% gm increment 8% ft increment (A: 220 GHz B:238 Lg)

II. The Design of Subchannel  AlAs/InAs Superlattice Structure (Channel Composition Modulation Transistor) (Ref. 7)  For high electron sheet carrier density and good carrier confinement and high electron transport  To improve the thermal stability of InP HEMT a) Epi-Structure b) Band Structure -0.12eV ->-0.17eV 20% improvement of electron confinement 0.2um T-Gate Mobility cm2/Vs ft=180GHz gm = 1370 ms/mm

III. Normal VS Inverted HEMT (Ref. 8) a) Normal InAs Inserted Channel HEMT : high output conductance and low breakdown voltage  InAs Inserted Channel Inverted HEMT : channel layer located on the carrier supply layer => low output conductance ( ∵ superior to electron confinement and smaller distance between gate and channel) C) Little kink-effect and a high breakdown voltage

III. Normal VS Inverted HEMT  The enhancement of mobility characteristic  The scattering cased by ionized donor and interface roughness Low effective mass and high mobility in Inverted HEMT

IV.AlSb/InAs HEMT (ref. 9) a) For high speed and low bias application ( ∵ high electron mobility and velocity, high sheet charge density and good carrier confinement) b) Disadvantage : charge control problem associated with impact ionization in the InAs channel (will increase as the Lg is reduced due to the higher fields present) a) Epi-Structure b) Band Structure

IV. AlSb/InAs HEMT  Lattice Matched System (Ref. 10) I. Current Status 1. Epitaxial Growth Buffer (interface roughness scattering) 2. Impact Ionization Effect a) dominant for short gate-length when the drain bias exceeds the energy bandgap in the channel => Thinner channel scheme (kink effect and low output conductance, transconductance and peak current density) need for trade-off of channel thickness and device performance. 6.1A lattice constant AlSb/InAs conduction band discontinuity 1.35eV

IV. AlSb/InAs HEMT  개선방안 a. Need a good buffer for good surface morphology and good carrier transport characteristic b. Thin InAs channel thickness

Conclusion I. Design of Subchannel Band a. InAs thickness for high speed and carrier confinement b. for better performance high sheet carrier density and mobility and carrier confinement (In0.8Ga0.2As/InAs/In0.8Ga0.2As channel) ∵ 3.5 % InAs mismatch in the channel  For Low kink effect and high breakdown voltage and the improvement of carrier mobility and sheet carrier density => Inverted HEMT III. For low cost and similar bandgap engineering compared with InP HEMT => AlSb/InAs HEMT

InAs Inserted HEMT  Reference 1. Modern Microwave Transistors theory, Design, and performance Frank Schwierz Juin J. Liou Wiley-Interscience 2. First principles band structure calculation and electron transport for strained InAs Hori, Y.; Miyamoto, Y.; Ando, Y.; Sugino, O.; Indium Phosphide and Related Materials, 1998 International Conference on, May 1998 Pages: Improved InAlAs/InGaAs HEMT characteristics by inserting an InAs layer into the InGaAs channel Akazaki, T.; Arai, K.; Enoki, T.; Ishii, Y.; Electron Device Letters, IEEE, Volume: 13, Issue: 6, June 1992 Pages: MBE growth of double-sided doped InAlAs/InGaAs HEMTs with an InAs layer inserted in the channel ARTICLE Journal of Crystal Growth, Volumes , Part 2, 1 May 1997, Pages M. Sexl, G. Böhm, D. Xu, H. Heiß, S. Kraus, G. Tränkle and G. Weimann 5. Impact of subchannel design on DC and RF performance of 0.1 μm MODFETs with InAs-inserted channel Xu, D.; Osaka, J.; Suemitsu, T.; Umeda, Y.; Yamane, Y.; Ishii, Y.; Electronics Letters, Volume: 34, Issue: 20, 1 Oct Pages: High electron mobility 18,300 cm2/V·s InAlAs/InGaAs pseudomorphic structure by channel indium composition modulation Nakayama, T.; Miyamoto, H.; Oishi, E.; Samoto, N.; Indium Phosphide and Related Materials, Conference Proceedings., Seventh International Conference on, 9-13 May 1995 Pages:

InAs Inserted Channel HEMT 7. InAlAs/InGaAs channel composition modulated transistors with InAs channel and AlAs/InAs superlattice barrier layer Onda, K.; Fujihara, A.; Wakejima, A.; Mizuki, E.; Nakayama, T.; Miyamoto, H.; Ando, Y.; Kanamori, M.; Electron Device Letters, IEEE, Volume: 19, Issue: 8, Aug Pages: Improving the characteristic of an InAlAs/InGaAs Inverted HEMT by inserting an InAs layer into the InGaAs channel Solid State Electronics vol. 38 NO. 5 pp Tatsushi Akazaki, Tatamoto Enoki, Kunihiro Arai and Yasunobu Ishi um AlSb/InAs HEMTs with InAs subchannel Electronics Letters 23 rd July 1998 Vol. 34 No.15 J.B boos, M.J. Yang, B.R. Bennett, D. Park, W. Kruppa, C.H. Yang and R. Bass 10. InAs channel HFETs: current status and future trends Bolognesi, C.R.; Signals, Systems, and Electronics, ISSSE URSI International Symposium on, 29 Sept.-2 Oct Pages: