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Center for Energy Efficient Electronics Science
A National Science Foundation Science & Technology Center
Investigating Band-Edge Sharpness in GaSb/InAs
Heterojunctions for Use in TFETs
Robert Orleans-Pobee1, Jared Carter2, Eli Yablonovitch2
Virginia Polytechnic Institute and State University1; UC Berkeley2
Abstract: While miniaturization has continued to develop according to Moore’s law, the overall pace of improvement is beginning to slow because power
requirements have remained largely the same. The leading source of power consumption in modern circuits is the Metal-Oxide Field-Effect Transistor
(MOSFET); therefore, in order to reduce power consumption a mechanism must be found to operate transistors at lower voltages. One proposed low-voltage
alternative to the MOSFET is the Tunneling Field-Effect Transistor (TFET), which operates by manipulating the quantum tunneling effect in a P-N junction. For
tunneling in a junction, the conduction band on one side must line up with the valence band on the other, a condition that is met in GaSb/InAs heterojunctions.
However, in order for these heterojunctions to be viable in transistors, the band edges must be extremely sharp. We intend to investigate the sharpness of these
band edges by developing a circuit for use in band-edge spectroscopy.
Data
Introduction
• Semiconductor band-edge sharpness extremely important
• Correlated to minimum switching voltage in devices
• Related to current-voltage (IV) curves
• Can create IV curves with increased accuracy using 1st and 2nd
derivative data
• Circuit created with calibration options in order to capture derivative
information
Fig 2: Sample data reading
Fig 3: Sample data sweep
• Red curve is applied voltage (Vapp+ vapp)
Circuit Design/Methods
• Vapp = 792.5mV
• vapp = 22.5mV
• White curve is voltage drop over Rm
• Rm= 12.1K
• Vm= 780 mV
• vm = 7.5mV
• I(792.5mV) = Vm / Rm = 65.50 mA
• dI/dV (792.5mV) = (vm / Rm) / vapp = 0.0275 mA/V
• Sweeping through different voltages as shown in Fig 3 allows calculation
of I vs V and dI/dV vs V curves
Discussion
Fig 1: Circuit diagram
• Stage 1: Voltage manipulation
• AC voltage (vapp) and DC voltage (Vapp) added over 1:1 Transformer
• Op-amps: OPA627BP and OP27E
• More sophisticated adding than connecting voltages in series
• Op-amps present suitably high input impedance to prevent current flow
• Prevents damage to sensitive AC voltage generator
• OPA627BP: 10 Teraohms
• Combined voltage buffered through op-amp
• Creates opportunity to place capacitor in op-amp feedback loop for
filtering
• Provides alternate current source, so that the DC and AC signal
generators are driving current
• OP27E: 3 Gigaohms
• Op-amp feedback loop allows for addition of capacitors for filtering
• Rm can be implemented as a potentiometer allowing resistances that create
good voltage drop over the diode
• 2nd derivative measurements can be obtained via measurement of harmonics
• Stage 2: Voltage application and measurement
• Buffered voltage applied over sample diode
• Voltage after diode voltage drop applied over measurement resistor
(Rm)
• Voltage drop over Rm buffered by instrumentation op-amp
• Buffered Rm voltage drop collected by DAQ card
Acknowledgements
I would like to thank my mentor, Jared Carter as well as the principal investigator
of my group, Dr. Eli Yablonovitch and the program director Dr. Sharnnia Artis.
Contact Information
Robert Orleans-Pobee at [email protected].
Support Information
This work was funded by
National Science Foundation
Award ECCS-0939514.