Metal-stable excited states in closed quantum dot probed by Al-SET

Jeng-Chung Chen

Sep 19 2006Condensed Matter SeminarDepartment of Physics / NTHU

Outline

Metal-stable excited states in closed

• Device characterization

• Excited electronic states in closed QD

• Discussion

• Conclusion

On-chip optical-coupled QH devices

• Passive THz scanning microscopes

• Emitter: Hot spots

• Detector QH detector

• Device design

• Future perspective

Introduction: Technological and biological length scales

Single Electron Transistor - Introduction

Lateral Confinement Technique

Shadow Evaporation Technique

Al

SEM picture

100nm

Eg. diameter ~ 0.5-0.2mCg ~100-10 aFC ~2-0.9 fF

Capacitive Charging Model

Lithographic size of QD : 570nm560nm

Device Characterization

(a)

Temperature: 70-100mK

)(20)(800

groundedin source/dra :

ACVDCVV

QD

SDSET

Meta-stable states of QD observed by Al-SET

F0

Qualitative Discussion

V1=-1.18V

V1=-1.18V fixedIn closed QD, regime 2-6

QDQDQD

QDQD

QDQD

NC

eVeU

NC

eVeU

NC

eVeU

2

2,

2

,12,1

2

,22,2

2

21

22

2,12,2,2 QD

Discussion: Emperical Model

QDcsg

SET Ue

CV

e

CN

2

12 2)(

Cc~58.8aF, C1sg2=3.12aF

U1U2

UQD

e

UVeU

e

UVeU

QDQDQDQD

QDQDQDQD

,12,,12,1

,22,,22,2

2)(1

2)(2

233.0 ,0122.0

885.0 ,33.0

,12,,12,11

,22,,22,22

QDQDQD

QDQDQD

Quantitative discussion

1. Kinetics of charging and discharging of closed quantum dots (QD) in a GaAs/AlGaAs heterostructure crystal are studied by an Aluminum single electron transistor (Al-SET) electrostatically coupled to the quantum dot.

2. The period and conductance of CB peaks of Al-SET associated with different gating conditions reveal several distinct regimes, strongly depending on the tunneling barriers of QD.

3. A lift-up and an uncovered sinking electron excited state with long life time are realized in the completely closed dot.

4. An empirical model is proposed to explain the physical origins of these transitions.

Conclusion – First part

Ref: J.C. Chen, et al. Phys. Rev. B, 74, 045321 (2006).