1 Motivation: Embracing Quantum Mechanics Feature Size Transistor Density Chip Size Transistors/Chip Clock Frequency Power Dissipation Fab Cost WW IC Revenue WW Electronics Revenue 1970Today 6 um ~10 mm kHz ~100 mW ~$10 M $700 M $70 B Change 90 nm ~400 mm M > 1 GHz ~100 W >$1 B $170 B $1.1 T 70x Reduction 5000x Increase 40x Increase 200,000x Increase >10,000x Increase ~1000x Increase >100x Increase 240x Increase 16x Increase High Performance 90nm Technology Node 256 million transistors 37nm gate length PNO gate: 10 nm EOT NiSi 2 /Poly gate 8 levels Cu with low-k interlevel dielectric High Performance 90nm Technology Node 256 million transistors 37nm gate length PNO gate: 10 nm EOT NiSi 2 /Poly gate 8 levels Cu with low-k interlevel dielectric 34 Years of History: More, More, Moore # transistor per IC Miniaturization  power dissipation  short channel effect  statistical error in dopant distribution  quantum mechanical effects – ballistic – tunneling Alternative schemes to embrace quantum mechanical effects – low power – fast – new functionality, e.g. spin Intel and IBM embracing spintronis Miniaturization  power dissipation  short channel effect  statistical error in dopant distribution  quantum mechanical effects – ballistic – tunneling Alternative schemes to embrace quantum mechanical effects – low power – fast – new functionality, e.g. spin Intel and IBM embracing spintronis

2 Successful Examples of Spintronics metal-based ferromagnetic devices Rapid transition from discovery to commercialization – 1988 giant magneto resistance (GMR) – 1998 IBM read head extends storage from 1 to 20Gbits ($100B) – 2004 Motorola MRAM with 10ns access time – Gbit memory chip projected Non-volatile, no wearout, fast write time, fast read time, low energy for writing, radiation-hard Rapid transition from discovery to commercialization – 1988 giant magneto resistance (GMR) – 1998 IBM read head extends storage from 1 to 20Gbits ($100B) – 2004 Motorola MRAM with 10ns access time – Gbit memory chip projected Non-volatile, no wearout, fast write time, fast read time, low energy for writing, radiation-hard past/ /17_Hummel_Mram.pdf spin valve hard drive read head spin valve hard drive read head magnetic tunneling junction memory GMR

3 Objective Demonstrate the essential elements required for ballistic spin devices – semiconductor spin-FET Demonstrate the essential elements required for ballistic spin devices – semiconductor spin-FET Essential elements: electrical (rather than optical) 1.injection of highly spin- polarized electrons 2.manipulation of electron spin orientation during coherent transport 3.spin-sensitive detection Essential elements: electrical (rather than optical) 1.injection of highly spin- polarized electrons 2.manipulation of electron spin orientation during coherent transport 3.spin-sensitive detection InAs spin transistor 100nm All existing semiconductor devices operate in the diffusive transport regime, where scattering results in heat dissipation and limits frequency response Spin transport in the ballistic regime offers opportunities which are heretofore unexplored and unexploited All existing semiconductor devices operate in the diffusive transport regime, where scattering results in heat dissipation and limits frequency response Spin transport in the ballistic regime offers opportunities which are heretofore unexplored and unexploited spin ballistic length

4 Semiconductor spintronics: Spin FET Datta and Das, Applied Physics Letters, 56, 665 (1990); 816 citations Gate controlled spin precession through Rashba spin-orbit coupling in 2D channel Ferromagnetic drain that provides:  low resistance if spins are parallel  high resistance if spins are anti-parallel Ferromagnetic source injects spin polarized electrons Not experimentally demonstrated yet Key processes face challenges Not experimentally demonstrated yet Key processes face challenges

5 Our Technical Approach: Electrical + InAs Key obstacle to study spin manipulation in InAs, ferromagnetic/InAs needed to develop FM/InAs hybrid junction, spin detection needed optical detection is not practical, electrical detection needed FM/InAs hybrid junction needed for electrical detection Challenges determination of  R control of  R optimization of  R Challenges optimal ferromagnetic Interface integrity etching selectivity Detection Electrical spin detection Efficiency of spin transport across FM/InAs junction Injection Electrical tunability of Rashba SO coupling in InAs Manipulation Our solution: a novel configuration for electrical spin injection and detection

6 Current Status: Ferromagnetic/GaAs Hybrid Junction Magnetic Metal / Tunnel Barriers GaAs Fe Schottky P QW 32% Tunneling P QW to 40% (lower bound, 5 K) Fe Al 2 O 3 GaAs Metal oxide Al 2 O 3 40% 5 meV  Fe AlGaAs GaAs Benchmark performance at 5K well-defined system state detector “purely” excitonic most well studied temperature APL 80, 1240 (2002) (NRL) APL 82, 4092 (2003) (NRL) (NRL)

7 Past Spin Research : Optical + GaAs GaAs band gap is ideal for optical experiments optically generate spin-polarized electrons detect spin populations with circularly polarized PL GaAs band gap is ideal for optical experiments optically generate spin-polarized electrons detect spin populations with circularly polarized PL Fe/barrier/GaAs NRL patent (1999) P circ P QW   Spin-Light Emitted DiodePump-Probe Studies of Spin Precession D. D. Awschalom, UCSB

8 Rashba Spin-Orbit Coupling In the absence of an external B z 2DEG in quantum well Structural Inversion Asymmetry z confinement potential B in rest frame B in moving frame relativistic effect In nature, spins are controlled with magnetic field. Thanks to spin-orbit coupling, now spins can also be controlled by using conventional gates. In nature, spins are controlled with magnetic field. Thanks to spin-orbit coupling, now spins can also be controlled by using conventional gates.

9 Optimal Material for Rashba Spin-Orbit Coupling Advantage of InAs Larger g* (15 vs. 2 vs. 0.44)  Larger spin splitting (meV) Smaller m* (0.023 vs vs. 0.19)  Larger quantization energy (10meV) Higher RT mobility (40k vs. 8k vs. 1.4k)  Longer mean free path (700nm) Advantage of InAs Larger g* (15 vs. 2 vs. 0.44)  Larger spin splitting (meV) Smaller m* (0.023 vs vs. 0.19)  Larger quantization energy (10meV) Higher RT mobility (40k vs. 8k vs. 1.4k)  Longer mean free path (700nm) GaAs Si InAs B IN (Tesla) 2 ħ  SO (meV)