James Kally Ventura College, Physics Major Mentor: Greg Dyer - - PowerPoint PPT Presentation

James Kally Ventura College, Physics Major Mentor: Greg Dyer Faculty Advisor: Prof. Jim Allen from The Department of Physics at UCSB In 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 detectors

Special type of transistor

Plasmonic THz Detector

THz radiation excites plasmons (electrons) Tunable, narrow-band detection

Focus on a single device

Measure THz response Correlate transport characteristics Develop 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 layer

AlGaAs GaAs Grating Gates Source Drain

Source Drain I

Grating 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 drain

Graph show variation over time

• Pinch off differs

I-V curve shows on and off state

• 3000 -2500 -2000 -1500 -1000
• 500

2 4 6 8 10 12 14

1149XM2, 7/11/2008 11:00 AM to 11:50 AM 3:00 PM to 3:50 PM

G (mS) VGate (mV)

Conductance vs. Gate Voltage

• 3000 -2500 -2000 -1500 -1000
• 500

2 4 6 8 10 12 14

1149XM2, 7/11/2008 1:09 PM to 1:26 PM 2:26 PM to 2:53 PM

G (mS) VGate (mV)

Conductance vs. Gate Voltage

• 10
• 5

5 10 15 20

• 10
• 5

5 10

Gate Voltage 0.0 mV

• 2800 mV

ISD (µA) Voltage (mV)

I-V

Source Drain

I

• 10
• 5

5 10

• 12
• 10
• 8
• 6
• 4
• 2

2 4

gate voltage

• 2750 mV
• 2800 mV

Corrected Response

Response (mV/W) ISD (µA)

Voltage shift when hit by THz radiation

• Hot electron effect (2D gas heating)
• 10
• 5

5 10

• 1.5
• 1.0
• 0.5

0.0 0.5

gate voltage

• 2750 mV
• 2800 mV

dV/dT (mV/K) ISD (µA)

dV/dT

Change in temperature from 20K to 25K

Source Drain

I

• 10
• 5

5 10 0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007

gate 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

5 10 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

gate voltage

• 2750 mV
• 2800 mV

dV/dI (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

Current Voltage ISD (µA)

response