InAs Inserted HEMT

2004.06.16연성진

contents

1.Introduction

2.Structure & Device performance

3.Improvement scheme

InGaAs/InAlAs HEMT

MaterialBandgap

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

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

Channel structure

Lower band gap material as channel material:

1. Higher Electron confinement2. Higher mobility3. Lower noise4. Lower sheet resistance5. higher saturation drift velocity

InGaAs channel InAs channel

InAs inserted HEMT

For Higher gain Higher frequency characteristics

Cap InGaAs

Barrier InAlAs

Channel InGaAs

Buffer InAlAs

Substrate InP

Cap InGaAs

Barrier InAlAs

Channel InGaAs

Buffer InAlAs

Substrate InP

SubChannel InAsChannel InGaAs

InGaAs/InAlAs HEMT InAs Inserted HEMT

Channel engineering

Channel total thickness: 300Å Target: Higher mobility Variable: InAs thickness, Upper I

nGaAs thickness Dependence on growth tech.

Device performance

0.1um T-Gate fT=290GHz @ Vds=0.5V Low drain bias voltage limitation o

wing 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

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

Hole accumulatio

n

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 m

obility at low fields) InP (low impact- ioniza

tion, 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 A

Structure BStructure C

Conclusion InAs Inserted HEMT

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 performanceDae-Hyun Kim; Tae-Woo Kim; Hun-Hee Noh; Jae-Hak Lee; Kwang-Seok Seo;Electron Devices Meeting, 2004. IEDM Technical Digest. IEEE International13-15 Dec. 2004 Page(s):1027 - 1030

2. First principles band structure calculation and electron transport for strained InAsHori, 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 channelAkazaki, 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 channelXu, 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 modulationNakayama, 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