Ferromagnet/Semiconductor Based Spintronic Devices.

Abstract

Spintronics is an emerging field which is great interest for its potential to provide high-speed and low-power novel devices and eventually replace and/or complement conventional silicon-based metal-oxide-semiconductor (MOS) devices. Spinbased optoelectronic devices provide improved laser performance and polarized light sources for secure communication. Spintronics has therefore received a lot of interest with the potential for conventional and novel applications. Spintronics has been investigated both in all-metal and semiconductor based platforms. Spin-based ferromagnet/semiconductor heterojunction devices are particularly attractive compared to all-metal spintronic devices due to the versatility and the long electron spin coherence time in semiconductors. Here we have investigated semiconductor based spintronic devices for logic, memory and communication applications. We have demonstrated electrical injection and detection of spin in a MnAs/GaAs lateral spin valve. A peak magnetoresistance of 3.6% at 10 K and 1.1% at 125 K have been measured in these devices. Spin polarization in semiconductors is usually very small and difficult to detect. We have therefore theoretically designed and experimentally demonstrated a spin-current amplifier to alleviate this problem. A spin polarization of 100% has been measured at 150 K in these devices. We have emphasized the importance of finite sizes of ferromagnetic contact pads in terms of two-dimensional spin-diffusion in lateral spintronic devices, which enhances spinpolarization. We have discovered a new phenomenon observing electrically driven spin-dynamics of paramagnetic impurities. We have demonstrated a spin-capacitor using this novel phenomenon.

In this study we have also demonstrated a spin-polarized quantum dot spin-laser which is a fundamental spin-based optoelectronic device. An output circular polarization of 8% and threshold current reduction of 14% have been measured at 200 K. We have also demonstrated electrical modulation of output circular polarization in a spin-VCSEL. We have highlighted the importance of spin-transport in spin-lasers by analytically solving carrier-photon coupled laser rate equations. We have finally demonstrated Magneto-Opto-Electronic Integrated Circuit (MOEIC), which monolithically integrates a spin-valve (magnetic), a LED (optoelectronic) and a cascaded HEMT amplifier (electronic), acting as a magneto-electronic switch. The operation of the MOEIC has been experimentally characterized.