1. Novel Architecture of Illuminable Variable Density Two-Dimensional Electron System S.Brandsen, J. Pollanen, J.P. Eisenstein Institute for Quantum Information and Matter (IQIM), Condensed Matter Physics, Caltech L.N. Pfeiffer, K.W. West Princeton Univ., Dept. of Electrical Engineering

2. 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

3. Beyond single particle physics Can we control interactions ? A zoo of collective electron ground states! B - field i V v=5/2

4. Single interface AlGaAs GaAs 2DES  dopants AlGaAs Conduction Band Valence Band GaAs

5. Cleaning up with light AlGaAs GaAs 2DES  dopants AlGaAs Conduction Band Valence Band GaAs

6. Conflict between light and gating AlGaAs GaAs 2DES  dopants VgVg

7. Transparent n+ layer GaAs AlGaAs Si n+ GaAs  dopants 2DES

8. Characterization of 2DES Etched n+ to depletion μ 2DES : 3x10 6 cm 2 /Vs, n 2DES: 1.2x10 11 carriers/cm 2 R xx (Ω) Field Strength (Tesla) n+ GaAs AlGaA s

9. Characterization of 2DES Diffused Ni/Au/Ge Contacts μ 2DES : 3x10 6 cm 2 /Vs, n 2DES: 1.2x10 11 carriers/cm 2 R xx (Ω) Field Strength (Tesla) n+ GaAs AlGaA s

10. Initial Characterization GaA s AlGaA s Diffused Ni/Au/Ge contacts μ 2DES : 3x10 6 cm 2 /Vs, n 2DES: 1.2x10 11 carriers/cm 2 Known values Fit Parameters R xx (Ω) Field Strength (Tesla) μ n+ : 3x10 4 cm 2 /Vs n n+ : 7.4x10 12 carriers/cm 2

11. Fabrication Procedure n+ AlGaAs Etch away n+ GaAs AlGaAs Si n+ GaAs  dopants 2DES GaAs AlGaA s

12. Fabrication Procedure n+ AlGaAs Diffused Ni/Au/Ge Contacts GaAs AlGaAs Si n+ GaAs  dopants 2DES GaAs AlGaA s

13. Fabrication Procedure n+ AlGaAs Shallow Pd/Au/Ge Contacts GaAs AlGaAs Si n+ GaAs  dopants 2DES GaAs AlGaA s

14. Fabrication Procedure n+ AlGaAs Shallow Pd/Au/Ge Contacts GaAs AlGaAs Si n+ GaAs  dopants 2DES GaAs AlGaA s

15. Density calibration of n+ sample 2 current in B - field

16. Increased Quality With Illumination 1 1 2 2 2/3

17. 300mK magneto-transport 2 1 1 1 1 2/3 2 2 2 2

18. Mobility of 2DES versus n

19. Conclusions Development of illuminable high mobility, variable density 2DES Potential to explore the role of charge density in 2DES phenomena

20. Effective Gating After Illumination 3000 Ω 1 1 2 2