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Nov 2, 2013 (4 years and 8 months ago)


Resonant Tunneling

Johnny Ling, University of Rochester

December 16
, 2006



Introduction to normal tunneling diode

Resonant tunneling diode

Advantages and Limitations



An increasing number of applications that require
signal sources at very high frequencies (300

Ultimate limit on the current trend of down
transistors and integrated circuits to achieve faster
speeds and lower power consumption

The highest frequency conventional transistor
oscillator built today is only about 215 GHz.

Tunneling diodes (TD)

N diode with heavy
doping (10

) in both
regions (Degenerately

The depletion region is
very narrow (<10nm)

High concentration of
electrons in the
conduction band of N
type and holes in the
valence band of P

Tunneling Diodes (cont.)

Apply increasing forward bias voltage

Starting at zero bias:

Tunneling Diodes (cont.)

Electrons in N
region conduction band are
energetically aligned to the holes in the valence
band of P
region. Tunneling occurs. Forward
current is produced.

Tunneling Diodes (cont.)

As you increase the bias voltage, a
maximum current will be produced when all
electrons are aligned with the holes

Tunneling Diodes (cont.)

As bias voltages continues to increase,
current will decrease because less electrons
are aligned with the holes

Tunneling Diodes (cont.)

As the bias voltage continues to increase,
electrons are no longer energetically aligned
with the holes and the diffusion current
dominates over tunneling

Tunneling Diodes (cont.)

Reverse bias voltage


High leakage current, not a good rectifier

Resonant Tunneling Diode (RTD)

Electrons must have a certain minimum energy above the
energy level of the quantized states in the quantum well in
order for tunneling to occur. Once the bias voltage is big
enough to provide enough energy, RTDs looks like a normal

In reverse bias, RTDs do not have large leakage current

Negative Differential Resistance(NDR)

Characterized by the current peak to valley ratio


To achieve maximize dynamic range, high PVR is desired.

To obtain maximum output power from RTD, high

current density is required

Decrease the thickness of the quantum well barrier

Increase emitter doping level

However, PVR will be decreased and leakage will

Advantages and Limitations

RTDs is considered among the fastest devices
because tunneling is very fast and is not transit
time limited as in CMOS technology, etc.

RTDs provide a low leakage current when a
reverse bias is applied.

Large dynamic range within a small input voltage

However, the output current and power of RTDs is
very limited compared to CMOS.


RTDs is much faster than any other conventional

Very important alternative as transistor technology
continues to scale down to the nanometer range

Very good rectifier

low leakage current

Much research needs to be done to improve

the output power and also to integrate them with

conventional transistors