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