James Kally Ventura College, Physics Major Mentor: Greg...
Transcript of James Kally Ventura College, Physics Major Mentor: Greg...
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James KallyVentura College, Physics Major
Mentor: Greg DyerFaculty Advisor: Prof. Jim Allen from The Department of Physics at
UCSBIn Partnership with Sandia National Laboratories
This project is funded by the National Science Foundation
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Terahertz Spectrum• Technology gap• Engineering difficulties • No known health risk
Applications in:• Medical• Military and Homeland Security• Categorizing proteins and molecules
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Characterize terahertz detectorsSpecial type of transistor
Plasmonic THz DetectorTHz radiation excites plasmons (electrons)Tunable, narrow-band detection
Focus on a single deviceMeasure THz responseCorrelate transport characteristicsDevelop a model of transport within the device
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High Electron Mobility Transistor (HEMT)
• Uses electrons for transport• Thin layer of electrons creating
2D electron gas• Gate is applied with negative
voltage to limit flow
• Grating Gates couples radiation with the 2D electron gas in the GaAs layerAlGaAs
GaAs
Grating Gates
Source
Drain
Source Drain
IGrating Gates
Finger Gate
Profile
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The Free Electron Laser (FEL) produces THz radiation
• This is done by sending electrons through a resonator
• The radiation is then positioned by mirrors and focused on the detector
Measure the Detectors response
• We go from a negative to positive current bias
• Then measure the voltage response
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Pinch off• Limits current between source
and drainGraph show variation over time
• Pinch off differs
I-V curve shows on and off state
-3000 -2500 -2000 -1500 -1000 -500 00
2
4
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1149XM2, 7/11/2008
11:00 AM to 11:50 AM3:00 PM to 3:50 PM
G (m
S)
VGate (mV)
Conductance vs. Gate Voltage
-3000 -2500 -2000 -1500 -1000 -500 00
2
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1149XM2, 7/11/2008
1:09 PM to 1:26 PM2:26 PM to 2:53 PM
G (m
S)
VGate (mV)
Conductance vs. Gate Voltage
-10 -5 0 5 10 15 20
-10
-5
0
5
10
Gate Voltage 0.0 mV -2800 mV
I SD (µ
A)
Voltage (mV)
I-V
Source
Drain
I
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-10 -5 0 5 10-12
-10
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-6
-4
-2
0
2
4
gate voltage -2750 mV -2800 mV
Corrected Response
Res
pons
e (m
V/W
)
ISD (µA)
Voltage shift when hit by THz radiation-Hot electron effect (2D gas heating)
-10 -5 0 5 10
-1.5
-1.0
-0.5
0.0
0.5 gate voltage -2750 mV -2800 mV
dV/d
T (m
V/K
)ISD (µA)
dV/dT
Change in temperature from 20K to 25K
Source
Drain
I
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-10 -5 0 5 100.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007gate voltage
-2750 mV -2800 mV
time
(ms)
ISD (µA)
Time Constant
Time for voltage to return to ground state(EQ)-Hot electron effect
-10 -5 0 5 100.00.20.40.60.81.01.21.41.61.82.0
gate voltage -2750 mV -2800 mV
dV/d
I (kΩ
)ISD (µA)
dV/dI
Change in resistance at the bias point
Source
Drain
I
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Summary• Data is reasonably close to other collected data• Plasmonic Terahertz detectors hold great potential• Have improved the stability of I-Vs
Future Research• Use of grating gates to tune the detector• Minimize grating gates• Optimize finger gate• Array of detectors
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• INSET• Partner: Sandia National Laboratories• Mentor: Greg Dyer• Faculty Advisor: Prof. Jim Allen• Allen Group
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Cur
rent
Voltage
ISD (µA)
response