InAs Inserted HEMT 2004.06.16 연성진

contents 1.Introduction 2.Structure & Device performance 3.Improvement scheme

InGaAs/InAlAs HEMT low noise and high frequency device Conduction Band 2DEG Fermi Level Energy band diagram of a HEMT low noise and high frequency device high electron mobility & high sheet carrier density high saturation drift velocity Material Bandgap Energy (eV) Electron Mobility (cm2/V·s) Peak Velocity (cm/s) Si 1.13 1,300 1.0x107 Ge 0.76 3,800 - GaAs 1.42 8,500 2.0x107 InP 1.26 4,600 2.7x107 InAs 0.35 27,000 4.2x107 In0.53GaAs 0.75 12,000 2.9x107

Channel structure Lower band gap material as channel material: InGaAs channel InAs channel Lower band gap material as channel material: Higher Electron confinement Higher mobility Lower noise Lower sheet resistance higher saturation drift velocity

InAs inserted HEMT For Higher gain Higher frequency characteristics Cap InGaAs Cap InGaAs Barrier InAlAs Barrier InAlAs Channel InGaAs Channel InGaAs SubChannel InAs Channel InGaAs Buffer InAlAs Buffer InAlAs Substrate InP Substrate InP InGaAs/InAlAs HEMT InAs Inserted HEMT For Higher gain Higher frequency characteristics

Channel engineering Channel total thickness: 300Å Target: Higher mobility Variable: InAs thickness, Upper InGaAs thickness Dependence on growth tech.

Device performance 0.1um T-Gate fT=290GHz @ Vds=0.5V Low drain bias voltage limitation owing to the increased output conductance

Low drain bias voltage limitation Low on-state breakdown Bias sweep limitation Drastic increment of output conductance Low Fmax By Impact ionization!

Impact Ionization process Hole accumulation 1. Impact Ionization 2. Electron-hole pair is generated 3. the hole is attracted to source region 4. hole accumulation in source region 5. electron is attracted from source by accumulated hole Carrier multiplication Positive Feedback

Lowering Impact Ionization rate Composite channel with low I.I threshold energy material Channel quantization

Composite channel (with low I.I threshold energy material ) Impact ionization threshold energy in InP is higher than in InGaAs or InAs wider band gap energy larger electron effective mass. => contribute to decreased impact ionization effects

InGaAs/InP composite channel HEMT Advantage of composite channel with InP: InGaAs or InAs (high mobility at low fields) InP (low impact- ionization, high saturation velocity)

Channel quantization Channel quantization with decreasing channel thickness Enhancement of the channel bandgap Increment of threshold energy for i.i =>reduces impact ionization effects in on-state breakdown

Application to InAs(1) Increment of Effective bandgap Reduction of impact Ionization hole current Reduction of saturation current level Composite channel

Application to InAs(2) Structure A: L1=9nm, (single side doped) Structure B: L1=2nm, (single side doped) Structure C: L1=2nm, (double side doped) Structure B Structure C

Conclusion InAs Inserted HEMT Lowering Impact Ionization rate Merit: Higher Gm Higher Ft Problem: Low bias voltage limitation (Low On-state breakdown voltage) Lowering Impact Ionization rate Composite channel Channel quantization

Reference 1. Suppression of kink phenomenon in ultra-high-speed strained InAs- inserted E-mode HEMTs with a new 0.1 /spl mu/m Y-shaped Pt-buried gate and their impacts on device performance Dae-Hyun Kim; Tae-Woo Kim; Hun-Hee Noh; Jae-Hak Lee; Kwang-Seok Seo; Electron Devices Meeting, 2004. IEDM Technical Digest. IEEE International 13-15 Dec. 2004 Page(s):1027 - 1030 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 , 11-15 May 1998 Pages:104 - 107 3. 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:325 - 327 4. MBE growth of double-sided doped InAlAs/InGaAs HEMTs with an InAs layer inserted in the channel  • ARTICLE Journal of Crystal Growth, Volumes 175-176, Part 2, 1 May 1997, Pages 915-918 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. 1998 Pages:1976 - 1977 6. 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, 1995. Conference Proceedings., Seventh International Conference on , 9-13 May 1995 Pages:733 - 736