1. High Electron Mobility Transistors
Abstract: HEMT is a field effect transistor incorporating a junction between two materials with different band gaps as the channel. We will discuss different types of HEMTs and their Applications.
Presented by: Date: 04/28/2014
Sujana Korrapati,
Sai Divya Anne

2. Outline Introduction GaN HEMT structure and operation principles
Design rules for AlGaN/GaN HEMT
InP HEMT
Comparison of GaN HEMT with GaAs HEMT
Applications in Technology
Summary

3. Introduction Transistors are used in electronic devices
e.g. switch, amplifiers, oscillators
To satisfy the growing demands of
High Power
High Speed
High Efficiency communications
Conventional HEMTs use a AlGaAs/GaAs AlGaN/GaN

4. Basic GaN HEMT Structure
Source:

5. Gallium Nitrate High electron density(Polarization effects)
Adequate for high power amplifiers High Breakdown voltage
Large heat capacity
Necessary to growth in a wafer of another material
Molecular Beam Epitaxy
Metal Organic Vapor Beam Epitaxy

6. Substrate Material Sapphire Silicon Carbide Silicon
Most used material, cheap, good quality commercial wafers.
Poor thermal conductivity.
Silicon Carbide
Low lattice mismatch.
High thermal capacity.
Silicon
Most common semiconductor.
Acceptable thermal conductivity.

7. Operation principles (Polarization)
AlGaN/GaN HEMTs transistor don’t need doping to obtain a high electron density. Spontaneous polarization. + Piezoelectronic polarization. = 1013 (cm2/Vs) carrier concentration

8. Enegry Band Diagram of GaN/AlGaN HEMT
HEMTs utilize heterojunction between two semiconducting materials to confine electrons to a triangular quantum well. 
Conduction band edge EC and Fermi level EF determine the electron density in the 2DEG
Source:

9. Heterojunction Heterojunction: 2 layers
Highly doped layer with grand gap
Non-doped layer with small gap

10. Design Rules For GaN/AlGaN HEMTs: Materials Perspective
Thickness of the Barrier Layer
Al composition of the barrier layer
Nucleation and Buffer layer
Substrate for epitaxial growth

11. Design Rules For GaN/AlGaN HEMTs: Fabrication Perspective
Gate footprint, cross-sectional area and width controls the frequency response
Gate drain spacing as well as gate footprint determines the breakdown voltage
Geometry of the device also plays a role

12. DC characteristics of GaN/AlGaN HEMTs

13. InP HEMT
Source:

14. Advantages of InP based HFETs
Lower noise
Higher cutoff frequency
Higher gain
Operating voltage below 3 V

15. Comparison of GaN HEMT with GaAs HEMTΦB
AlGaN
GaN Ec
∆Ec EF d
σcomp
AlGaAs donor σB
+ve
GaAs buffer
layer
2 DEG
σsurf
AlGaAs spacer
AlGaN/GaN HEMT
AlGaAs/GaAs HEMT

16. HEMT Applications
A Monolithic HEMT Passive Switch for Phased- Array Applications
High Power and High Efficiency GaN-HEMT for Microwave Communication Applications
Highly efficient high power InP HEMT amplifiers for high frequency applications
Highly Uniform InAlAs–InGaAs HEMT Technology for High-Speed Optical Communication System ICs

17. A Monolithic HEMT Passive Switch for Phased- Array Applications
A 0.2 x 200 ,um2 HEMT device is used as a series passive FET switch

18. High Power and High Efficiency GaN-HEMT for Microwave Communication Applications
In the typical mobile communication band of more than 2GHz, the RF signal loss through the Cds and Rs becomes significant. Thus, the minimization of Cds is effective in the high efficiency amplification.

19. InAlAs–InGaAs HEMT Technology for High-Speed Optical Communication System ICs
Uniformity of the transistors is required to fabricate high-speed ICs
ICs with more than 1000 transistors were fabricated using Y-shaped gate technology and operated at 40 Gb/s

20. Summary & Conclusions
HEMT transistor are widely used in electronic application
AlGaN/GaN structure looks promising
AlGaN/GaN HEMT grown on Si substrate not only reduces the production cost but also prepares for the possible combination of GaN devices and Si technology

21. References
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“Characterization of advanced AlGaN HEMT structures” Anders Lundskog.
arnumber=877122

22. Five Key Points about HEMT
3 contacts:
Source and drain  ohmic contacts.
Gate Schottky barrier
Conventional HEMTs use a AlGaAs/GaAs AlGaN/GaN
High electron density (Polarization effects)
The HEMT-HBT monolithic microwave integrated circuit (MMIC) is fabricated using selective molecular beam epitaxy (MBE)
InAlAs-InGaAs HEMT grown on InP substrate promises excellent gain and noise performance for amplifier applications

23. Questions ??