1140.120.11.120

Probing Semiconductor Nanostructures by a Pulsed Phase-Lock-Loop System

Yuen-Wuu Suen

Department of Physics, National Chung Hsing University

孫允武中興大學物理系

2140.120.11.120

OUTLINES

1. How it works

2. The home-brewed pulsed phase-lock-loop system

3. Some preliminary results for two-dimensional electron systems (2DES)

4. What can we do next?

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Detection by Phase Lock Loop (PLL)

phase=1=11PLL system

s=ss

0 =1+ s =11+s(B)s

0 =0 (by tuning )=1+ s(B) =11+s(B)s

=1/1+s(B)s

B:the parameter (magnetic field, excitations, temperature, etc) changed in the experiment

can be measured very accurately.

sample

known

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Type-II PLL

Sample under detection

Sample under detectionSAW Delay-LineCoplanar Waveguide (CPW)

Basic scenario

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2

2

00 )／(1

1

2 Mxx

effK

Lf

f

σ

2

2

SAW )/(1

/

2 Mxx

MxxeffKk

σσσσ

L

)( 210 M

GaAs:3.6×10-7 -1

GaAs/LiNO3(Y-Z):1.8×10-6 -1

2

,2, 00 fq xxxx

SAW Delay-Line

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Electric field

50 meandering CPWtotal length s

xx

0,0 qxx

m2

12

eff

D

dG

Coplanar Waveguide (CPW)

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Some formulae about lossy CPW:

1m)()( CjGLjjj

m

F0 eff

LC ,

eff

r

C

LZ

0

00

11

m

12

12

eff

D

d

G

m

Np

2

m

rad

8

11

2

1

0

2 ln}Re{

Z

dDxx

Ls

sxx

L

Z

d

Zd

00

}Im{

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Where to put the nanostructures (QDs, QWs, QXs…..) on the sensors?

for CPW for SAW

You don’t need to connect the QDs one by one!

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What kind of information we can get?

Microwave adsorption , dynamics at microwave frequencies…

coming from:

intraband adsorption

cyclotron resonance

spin flipping, spin rotations, spin-spin interaction, spin-orbit interaction---for “spintronics”??

spinsE

Magnetic field

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Schematic of a homemade PLL system for microwave signals up to 18 GHz.

FM

The phase resolution is about 0.001 degree even under very low average input power (~-100dBm).

A special designed homodyne amplitude detection scheme also allows us to detect very small microwave adsorption.

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A homodyne amplitude detection scheme

0º 90º

Ref. Signal (LO)

Signal from the sample

90º hybrid

Power splitter

mixerTo PLL

To amplitude detection

~0

A home-made vector meter??

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Why pulsed?

1. Use low average power to prevent from heating

2. Use gated averaging technique to avoid direct EM interruption

3. Avoid the reflection and multiple reflection signals

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Signal Gating & Averaging:

RF/Microwave pulse train

3~4 ms set by a lock-in amp

~200 s set by a pulse generator

0.2~2 s set by a pulse shaping circuit

s1(t)

s1(t)

sampling delay set by a pulse generator

sampling gate set by a pulse generatorfed into the controlling node of a sample-and-hold circuit

s3(t)

time delays2(t) signal of mixer

Direct coupled EMReflected signals s4(t) signal after SH

Peak power about –30~-70dBm

fed into lock-in

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Typical data for CPW on 2DES:

0 2 4 6 8 10

0

2

4

6

8

10

Am

plitu

de (a

rb. u

nit)

200kHz=2 =1

f0=1.39GHz

B (T)

amplitude

f

(a) The pattern of the meandering coplanar waveguide. (b) The amplitude and the frequency deviation f vs magnetic field B are shown for f0=1.39GHz at T=0.3K.

(a) (b)

Re{xx}

Im{xx}

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0 2 4 6 8 10

f0=

T=0.3K

2.16G

=2 =1

1.74G

0.59G

0.96G

1.39G

500kHz

f

B (T)

2.92G

0 2 4 6 8 105

10

15

20

25

30

f0=

=2 =1

2.92G

2.16G

1.74G

1.39G

0.96G

0.59G

Am

plitu

de (

arb.

uni

t)

B (T)

More data:

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0.0 0.1 0.2 0.3 0.4 0.5 0.6-0.15

-0.10

-0.05

0.00

0.05

0.10

0.59GHz 0.96GHz 2.12GHz 2.92GHz

Im{

xx}

(e2 /h

)

Re{xx

} (e2/h)0.0 0.2 0.4 0.6 0.8

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.96GHz

Im{

xx}

(e2 /h

)

Re{xx

} (e2/h)

2.12GHz 2.92GHz

0.59GHz

Some plots for scaling analysis

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Perspective

We have developed a potent and very sensitive tool for studying microwave properties of low-dimensional systems.

What Next?

Put CPW on substrate with nanostructures.

Put nanostructures on substrate with CPW.

Add bias or other excitations.