Lifetime and Spin Relaxation Time Measurements of Micro-Fabricated GaAs Tips

The lifetime and the spin relaxation time of excited electrons in GaAs microtips tailored for scanning tunneling microscope (STM) with spin polarization detection were measured by time-resolved polarized photoluminescence at room temperature. The electron lifetime obtained from the tip-fabricated p-type GaAs substrate was about 20 ps shorter than that obtained from the GaAs substrate without microtips. This is attributed to the enhanced surface recombination in the microtip. The spin relaxation time was comparable to the electron lifetime for the tip-fabricated GaAs substrate. From electron lifetime and spin relaxation time, a respectable spin polarization of about 20% was evaluated in the tip-fabricated GaAs substrate, which was about 1.2 times larger than that in the GaAs substrate without microtips, under the 0° incident angle of the excitation light. The influence of oblique incidence of the excitation light is also discussed.