K. Nontapot

Relaxation of photoinduced spins and carriers in ferromagnetic InMnSb films

The authors report time resolved measurements and control of photoinduced spin and carrier relaxations in InMnSb ferromagnetic films with 2% Mn content (grown by low-temperature molecular beam epitaxy) using femtosecond laser pulses, and compare them to analogous measurements on InBeSb and InSb films. In this work, magneto-optical Kerr effect and standard pump-probe techniques provided a direct measure of the photoexcited spin and carrier lifetimes, respectively. They observe decrease in relaxations times in the high laser fluence regime and an absence of temperature dependence of the relaxation times.

Time resolved measurements of spin and carrier dynamics in InAs films

We report time resolved measurements of spin and carrier relaxation in InAs films with carrier densities of 1.3×1016 and 1.6×1016cm−3 grown on (001) and (111) GaAs, respectively. We used standard pump-probe and magneto-optical Kerr effect spectroscopy at different excitation wavelengths, power densities, and temperatures. We observed sensitivity of carrier and spin relaxation time to the photoinduced carrier density but not to the variation in temperature. We explain our results using the Elliot–Yafet picture of spin relaxation process in narrow gap semiconductors.We report time resolved measurements of spin and carrier relaxation in InAs films with carrier densities of 1.3×1016 and 1.6×1016cm−3 grown on (001) and (111) GaAs, respectively. We used standard pump-probe and magneto-optical Kerr effect spectroscopy at different excitation wavelengths, power densities, and temperatures. We observed sensitivity of carrier and spin relaxation time to the photoinduced carrier density but not to the variation in temperature. We explain our results using the Elliot–Yafet picture of spin relaxation process in narrow gap semiconductors.

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.

Carrier Dynamics in Parabolic InSb Based Multi Quantum Wells

We report on time resolved differential transmission experiments in InSb/AlxIn1‐xSb multi‐parabolic quantum wells in the mid‐infrared. The results of our numerical calculations, which included band non‐parabolicity and the digital composition of the parabolic wells, allowed us to identify and probe the possible interband transitions. Our results provide new information on the carrier relaxations in this material system.

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.