James Kally Ventura College, Physics Major Mentor: Greg ...inset-csep.cnsi.ucsb.edu/.../files/james-kally...James Kally Ventura College, Physics Major Mentor: Greg Dyer Faculty Advisor:
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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
Terahertz Spectrum• Technology gap• Engineering difficulties • No known health risk
Applications in:• Medical• Military and Homeland Security• Categorizing proteins and molecules
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
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
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
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
6
8
10
12
14
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
4
6
8
10
12
14
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
-10 -5 0 5 10-12
-10
-8
-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
-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
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
• INSET• Partner: Sandia National Laboratories• Mentor: Greg Dyer• Faculty Advisor: Prof. Jim Allen• Allen Group
Cur
rent
Voltage
ISD (µA)
response
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