1. 140.120.11.120 1 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

2. 140.120.11.120 2 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?

3. 140.120.11.120 3 Detection by Phase Lock Loop (PLL) phase=  1 =  1 1 PLL system  s =  s s  0 =  1 +  s =  1 1 +  s (B) s  0 =0 (by tuning  ) =  1 +   s (B) =  1 1 +  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

4. 140.120.11.120 4 Type-II PLL Sample under detection SAW Delay-Line Coplanar Waveguide (CPW) Basic scenario

5. 140.120.11.120 5 L GaAs:3.6×10 -7  -1 GaAs/LiNO 3 (Y-Z):1.8×10 -6  -1 SAW Delay-Line

6. 140.120.11.120 6 Electric field 50  meandering CPW total length s Coplanar Waveguide (CPW)

7. 140.120.11.120 7 Some formulae about lossy CPW:

8. 140.120.11.120 8 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!

9. 140.120.11.120 9 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”?? spins E Magnetic field

10. 140.120.11.120 10 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.

11. 140.120.11.120 11 A homodyne amplitude detection scheme 0º0º90º Ref. Signal (LO) Signal from the sample 90º hybrid Power splitter mixer To PLL To amplitude detection ~0 A home- made vector meter??

12. 140.120.11.120 12 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

13. 140.120.11.120 13 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) s1(t)s1(t) sampling delay set by a pulse generator sampling gate set by a pulse generator fed into the controlling node of a sample-and-hold circuit s3(t)s3(t) time delay s 2 (t) signal of mixer Direct coupled EM Reflected signals s 4 (t) signal after SH Peak power about –30~-70dBm fed into lock-in

14. 140.120.11.120 14 Typical data for CPW on 2DES: (a) The pattern of the meandering coplanar waveguide. (b) The amplitude and the frequency deviation  f vs magnetic field B are shown for f 0 =1.39GHz at T=0.3K. (a) (b) Re{  xx } Im{  xx }

15. 140.120.11.120 15 More data:

16. 140.120.11.120 16 Some plots for scaling analysis

17. 140.120.11.120 17 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.