M. Frazier

Photoinduced spin-polarized current in InSb-based structures

National Science Foundation - Grant Nos. NSF-DMR-0507866, NSF-DMR-0603752, NSF-DMR-0520550, and NSF-DMR-0618235

Time resolved magneto-optical studies of ferromagnetic InMnSb films

We report time resolved magneto-optical measurements in InMnSb ferromagnetic films with 2% and 2.8% Mn contents grown by low temperature molecular beam epitaxy. In order to probe a possible interaction between the spins of photoexcited carriers and the Mn ions, we measured spin dynamics before and after aligning the Mn ions by applying an external magnetic field at temperatures above and below the samples’ Curie temperatures. We observed no significant temperature or magnetic field dependence in the relaxation times and attribute the observed dynamics entirely to the relaxation of photoexcited electrons in the conduction band where the s-d coupling with the localized Mn ions is significantly weaker compared to the p-d exchange coupling. We observed several differences in the optical response of our InMnSb samples which could have been influenced mainly by the samples’ growth conditions.

Control and Probe of Carrier and Spin Relaxations in InSb Based Structures

Narrow gap semiconductors (NGS) offer several scientifically unique features important for the field of spintronics. In order to explore these features we are using standard pump-probe and magneto-optical Kerr effect (MOKE) spectroscopy at different excitation wavelengths, power densities, and temperatures. Our goal is measuring and controlling carrier/spin relaxation in a series of InSb-based quantum wells and films, and InMnSb ferromagnetic films. The dynamic effects observed in these structures demonstrate strong dependence on the photo-induced carrier density.

Probe of Coherent and Quantum States in Narrow-Gap Semiconductors in the Presence of Strong Spin-Orbit Coupling

In light of the growing interest in spin-related phenomena and devices, there is now a renewed interest in the science and engineering of narrow gap semiconductors. They offer several scientifically unique electronic features such as a small effective mass, a large g-factor, a high intrinsic mobility, and large spin-orbit coupling effects. Our studies have been focused on probing and controlling the coherent and quantum states in InSb quantum wells and InMnAs ferromagnetic semiconductors. Our observations are providing new information regarding the optical control of carriers and spins in these material systems. We demonstrated the generation of spin polarized photo-current in an InSb QW where a non-equilibrium spin population has been achieved by using circularly polarized radiation. In addition, the differential transmission measurements in InSb QWs demonstrated that the initial distribution function strongly influences the carrier relaxation dynamics. We employed the polarization-resolved differential transmission as well as the MOKE measurements to provide information on the spin relaxation dynamics in MOVPE grown InMnAs. Our measured T1 is comparable to the reported measurements in MBE grown InMnAs and several time resolved measurements on InAs.