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)
As Lg decreases, an appropriate aspect ratio has to be maintained to alleviate short channel Effect.
Also, Channel thickness has to be reduced for proper aspect ratio (∵ The thinning of barrier layer is limited by current tunneling)
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)
Carrier Transport Characteristic
(Ref. 6)
Issue of the InAs Inserted HEMT
I. The Design of Subchannel of InAs for composite channel
=> 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
=> The strain brings about an increase of the InAs band gap of 0.12eV
Physics
Monte Carlo Simulation
Include polar optical phonon scattering and inter-valley deformation potential scattering at 300K
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
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) 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.
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 , 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
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. 1998 Pages:300 - 302
8. 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 pp997-1000 1995
Tatsushi Akazaki, Tatamoto Enoki, Kunihiro Arai and Yasunobu Ishi
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, 1998. ISSSE 98. 1998 URSI International Symposium on , 29 Sept.-2 Oct. 1998 Pages:56 - 61
