Resonant and Time Resolved Spin Noise Spectroscopy of Electron Spin Dynamics in Semiconductors.

Abstract

Determining the spin properties of novel materials is necessary for the development of proposed spin-based information processing devices, or spintronics. While existing optical techniques work for some semiconductors, they are ineffective for other strategic material systems. In this dissertation, we explore gallium arsenide bismuthide alloys and irradiated gallium arsenide using conventional methods. We then introduce the novel techniques of Resonant and Time Resolved Spin Noise which may enable optical studies of previously inaccessible materials.

Gallium arsenide bismuthide has a large tunable spin-orbit splitting, which could be desirable for spintronic applications. Hanle effect measurements reveal that the product of the g factor and effective spin lifetime (gTs) ranges from 0.8 ns at 40 K to 0.1 ns at 120 K, while below 40 K there was negligible change. The temperature dependence of gTs shows evidence of thermally activated behavior attributed to hole localization at Bi or Bi cluster sites.

Modern electronics are sensitive to radiation damage and require extensive modification for use in space, nuclear robotics, and other environments, but the effects of long term exposure on spin properties had not previously been investigated. Time Resolved Kerr Rotation measurements of irradiated gallium arsenide reveal robust spin behavior to 5 MeV protons up to a 10^14 p/cm^2 fluence, even as photoluminescence intensity decreases by two orders of magnitude.

Spin noise measurements are sensitive and capable of surpassing more established methods. However, the majority of schemes are restricted to Fourier analysis, record all sources of noise, and suffer digitizing restrictions. Since digitization involves discrete binning, amplitude resolution is limited by background fluctuations. Our novel techniques, Resonant and Time Resolved Spin Noise, bypass these issues using ultrafast laser pulses in tandem with analog electronic calculations that remove the background prior to digitizing. In principle, our system's accessible bandwidth for spin dynamics is 10 THz with sub-nanoradian/ Hz^(1/2) signal resolution using commercially available components. We demonstrate this measurement technique on a bulk n-type gallium arsenide sample and extract values for the g factor and dephasing time that are consistent with results from Time Resolved Faraday Rotation and Resonant Spin Amplication.