Terahertz waves base on SiGe Alloy
NTU
林楚軒
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Introduction
Structure
a.SiGe QW intersubband transition
b.SiGe QW with dopant helping
c.Si with dopant
Summary
Terahertz region
?THz=300/l(mm)
Applications
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Medical imaging
Biological weapon detection
Security monitoring
Gas sensing
Molecular spectroscopy
etc…
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Introduction
Structure
a.SiGe QW intersubband transition
b.SiGe QW with dopant helping
c.Si with dopant
Summary
Cascade emitters
We must let the upper state population inversion,and
it can emit from upper to lower state by photon.
Lower state of n+2 layer couples with upper state of
n+1,and hole injection can produce population inversion
except the first layer which hole current meets
(1)LH1 to HH1
16-period superlattice of 2.2 nm
Si0.7Ge0.3 QWs, with 3 nm Si
barriers , showing a peak at 350
cm-1 (10.5 THz).
Spectroscopy (FTIR) in the stepscan mode using a 0.5 % duty
cycle with 500 ns pulses at a 413
Hz repetition rate, to avoid device
heating that produces black body
This is theoretical calculation
about the level in quantum
well.
Levels in valence band is
splitted by strain
Si/Si0.7Ge0.3/Si QW
(2)HH2 to HH1
a
b
(3)more experiment data
30 periods of 5nm i-Si barriers with 8 nm i-Si0.72Ge0.28 quantum wells
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Introduction
Structure
a.SiGe QW intersubband transition
b.SiGe QW with dopant helping
c.Si with dopant
Summary
Resonant-state terahertz laser
B d-layer
20 nm thick Si0.85Ge0.15 QW was grown on a 130 nm
thick Si buffer layer and d-doped in the middle with
boron; concentration of B was 6*1011 cm-3.
mechanism
Acceptor levels in QW will
splitted by strain.
E1hh is the lowest space –
quantization level of
valence band,and E1s
resonate with it.
THz lasing when holes
transit from E1s to lower
splitted acceptor levels
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Introduction
Structure
a.SiGe QW intersubband transition
b.SiGe QW with dopant helping
c.Si with dopant
Summary
P-type Si
NA ~ 1e16 to 1e15 cm-3, at a
temperature of 4K.
The emission happens with
resistivity of 1-10 ohm-cm,
while samples fabricated from
undoped Si (>1000 ohm-cm),
and highly doped (0.01 ohmcm) bulk silicon did not yield
THz emission.
N-type Si
Phonon-assisted relaxation of
captured electrons has similarity
of the hydrogen-like states
involved donor in the process.
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
Introduction
Structure
a.SiGe QW intersubband transition
b.SiGe QW with dopant helping
c.Si with dopant
Summary
Summary
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There are 3 main kinds of terahertz
lasing(2 kinds take use of SiGe alloy)
THz by Si with dopant must be
operated at very low temperature
(advantage of SiGe alloy)