Novel Architecture of Illuminable Variable Density Two-Dimensional Electron

SystemS.Brandsen, J. Pollanen, J.P. Eisenstein

Institute for Quantum Information and Matter (IQIM), Condensed Matter Physics, Caltech

L.N. Pfeiffer, K.W. WestPrinceton Univ., Dept. of Electrical Engineering

Outline

• Two-Dimensional Electron System: Collective electron states

• Question: Phenomena as a function of charge density?

• Illuminable Variable Density Two-Dimensional Electron System: Fabrication, Magnetotransport, Future Uses

Beyond single particle physics

Can we control interactions ?

A zoo of collective electron ground states!

VH

B - fi

eld

i

Vv=5/2

Single interface

AlGaAs

GaAs

2DES d dopants

AlGaAs

Conduction Band

Valence Band

GaAs

Cleaning up with light

AlGaAs

GaAs

2DES d dopants

AlGaAs

Conduction Band

Valence Band

GaAs

Conflict between light and gating

AlGaAs

GaAs

2DES d dopantsVg

Transparent n+ layer

GaAs

AlGaAs

Si Si Sin+ GaAs d dopants2DES

Characterization of 2DES

Etched n+ to depletion

μ2DES : 3x106 cm2/Vs, n2DES: 1.2x1011 carriers/cm2

R xx (Ω

)

Field Strength (Tesla) n+

GaAs

AlGaAs

Characterization of 2DES

Diffused Ni/Au/Ge Contacts

μ2DES : 3x106 cm2/Vs, n2DES: 1.2x1011 carriers/cm2

R xx (Ω

)

Field Strength (Tesla) n+

GaAs

AlGaAs

Initial Characterization

GaAs

AlGaAs

DiffusedNi/Au/Ge contacts

μ2DES : 3x106 cm2/Vs, n2DES: 1.2x1011 carriers/cm2

Known values

Fit Parameters

R xx (Ω

)

Field Strength (Tesla)

μn+: 3x104 cm2/Vsnn+ : 7.4x1012 carriers/cm2

Fabrication Procedure

n+AlGaAs

Etch away n+GaAs

AlGaAs

Si Si Sin+ GaAs d

dopants2DES

GaAs

AlGaAs

Fabrication Procedure

n+AlGaAs

Diffused Ni/Au/Ge Contacts

GaAs

AlGaAs

Si Si Sin+ GaAs d

dopants2DES

GaAs

AlGaAs

Fabrication Procedure

n+AlGaAs

Shallow Pd/Au/Ge Contacts

GaAs

AlGaAs

Si Si Sin+ GaAs d

dopants2DES

GaAs

AlGaAs

Fabrication Procedure

n+AlGaAs

Shallow Pd/Au/Ge Contacts

GaAs

AlGaAs

Si Si Sin+ GaAs d

dopants2DES

GaAs

AlGaAs

Density calibration of n+ sample

2

VH

curre

nt in

B - fi

eld

Increased Quality With Illumination

1

1

2

2

2/3

300mK magneto-transport

2

1

1

1

1

2/3

2/3

2/3

2/32

2

2

2

Mobility of 2DES versus n

Conclusions

• Development of illuminable high mobility, variable density 2DES

• Potential to explore the role of charge density in 2DES phenomena

Effective Gating After Illumination

300

0 Ω

1

12

2