ECE3080-L-12b-AdvancedFETDevices

ECE3080-L-12b-AdvancedFETDevices - Lecture 12b Advanced...

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ECE 3080 - Dr. Alan Doolittle Georgia Tech Lecture 12b Advanced Field Effect Transistor (FET) Devices Reading: (Cont’d) Notes and Anderson 2 Chapter 8.11 Some images from Anderson and Anderson text
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ECE 3080 - Dr. Alan Doolittle Georgia Tech Advanced Devices: FET Devices High Electron Mobility Transistor (HEMT) The cross-sectional schematic (a) of a GaAs- based Heterostructure Field Effect Transistor (HFET) or High Electron Mobility Transistor (HEMT) and (b) the energy band diagram normal to the gate. The Schottky barriers at the metal-AlGaAs and metal-GaAs interfaces are thin enough to be of low resistance because of tunneling. Doping is removed from the channel increasing mobility significantly.
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ECE 3080 - Dr. Alan Doolittle Georgia Tech The channel is a 2D electron gas contained in the triangular quantum well created by the Ec of the AlGaAs- GaAs heterojunction. Also known as a MODFET, HFET, TEGFET, SDHT. Advantages: The mobility is not degraded by surfaces or interfaces like in a MOSFET. The AlGaAs-GaAs interface is lattice matched and thus has ZERO interface states. In a 2D electron gas (channel) the electron scattering is reduced by a factor of approximately x 2/3 making the mobility higher than in bulk. Some of this increase is due to separation of the dopants from the channel (modulation doping) and a small additional enhancement is due to the quantum 2D nature of the channel. Example: Bulk GaN µ ~1000-1200 cm 2 /V-Sec but in an AlN/GaN channel, µ ~2000 cm 2 /V-Sec . The device is very fast because the channel thickness can be very precisely controlled (minimized) making the channel easy to deplete with a small gate voltage. Advanced Devices: FET Devices High Electron Mobility Transistor (HEMT) E 1 E 2
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ECE 3080 - Dr. Alan Doolittle Georgia Tech The channel is a a strained lattice 2D electron gas contained in the triangular quantum well created by the Ec the AlGaAs-InGaAs heterojunction. Advantages: Higher channel charge (higher conductivity) due to a higher Ec for InGaAs vs GaAs Channels Higher saturation velocity of InGaAs results in higher frequency operation Lower Noise. Higher mobility of InGaAs results in smaller parasitic resistances and higher low field electron
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This note was uploaded on 08/23/2011 for the course ECE 3080 taught by Professor Staff during the Spring '08 term at Georgia Tech.

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ECE3080-L-12b-AdvancedFETDevices - Lecture 12b Advanced...

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