Terahertz waves base on SiGe Alloy

NTU

林楚軒

Introduction Structure a.SiGe QW intersubband transition b.SiGe QW with dopant helping c.Si with dopant Summary

Terahertz region

?THz=300/m

Applications Medical imaging Biological weapon detection Security monitoring Gas sensing Molecular spectroscopy etc…

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 step-scan 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 emission .

This is theoretical calculation about the level in quantum well.

Si/Si0.7Ge0.3/Si QW

Levels in valence band is splitted by strain

(2)HH2 to HH1a b

(3)more experiment data

30 periods of 5nm i-Si barriers with 8 nm i-Si0.72Ge0.28 quantum wells

Introduction Structure a.SiGe QW intersubband transition b.SiGe QW with dopant helping c.Si with dopant Summary

Resonant-state terahertz laser

B -layer

20 nm thick Si0.85Ge0.15 QW was grown on a 130 nm thick Si buffer layer and 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

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 ohm-cm) 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.

Introduction Structure a.SiGe QW intersubband transition b.SiGe QW with dopant helping c.Si with dopant Summary

Summary 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)