ABSTRACT
The GaAs semiconductor structures for the application as betavoltaic power sources were investigated. Three types of structures underwent a comparative study: a Schottky diode, a p-n junction and Schottky structure modified by deposition of a carbon layer. The power characteristics were estimated by Monte-Carlo simulation and collected current calculation using parameters obtained from the electron beam induced current technique. It was shown that carbon deposition on the top of n-GaAs allows passivating the surface states and thus improving betavoltaic performance.
ABSTRACT
Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a typical time evolution of the optically-oriented electron spin in the quantum well. Surprisingly, this is strongly affected by the Mn spins, resulting in an increase of the spin precession frequency in time. This increase is attributed to the variation in the effective magnetic field induced by the dynamical relaxation of the Mn spins. Two processes are observed during electron spin precession: a quasi-instantaneous alignment of the Mn spins with photo-excited holes, followed by a slow alignment of Mn spins with the external transverse magnetic field. The first process leads to an equilibrium state imprinted in the initial precession frequency, which depends on pump power, while the second process promotes a linear frequency increase, with acceleration depending on temperature and external magnetic field. This observation yields new information about exchange process dynamics and on the possibility of constructing spin memories, which can rapidly respond to light while retaining information for a longer period.
ABSTRACT
We investigated the dynamics of the interaction between spin-polarized photo-created carriers and Mn ions on InGaAs/GaAs: Mn structures. The carriers are confined in an InGaAs quantum well and the Mn ions come from a Mn delta-layer grown at the GaAs barrier close to the well. Even though the carriers and the Mn ions are spatially separated, the interaction between them is demonstrated by time-resolved spin-polarized photoluminescence measurements. Using a pre-pulse laser excitation with an opposite circular-polarization clearly reduces the polarization degree of the quantum-well emission for samples where a strong magnetic interaction is observed. The results demonstrate that the Mn ions act as a spin-memory that can be optically controlled by the polarization of the photocreated carriers. On the other hand, the spin-polarized Mn ions also affect the spin-polarization of the subsequently created carriers as observed by their spin relaxation time. These effects fade away with increasing time delays between the pulses as well as with increasing temperatures.
ABSTRACT
Spectral dependences of the transversal Kerr effect (TKE) as well as of the real and imaginary parts of the permittivity of InMnAs layers were studied. Pulsed laser ablation of Mn and InAs targets was used to form the layers on GaAs(100) substrates. Spectra of the optical constants and TKE depended substantially on layer fabrication conditions and testified to the presence of MnAs inclusions in the samples. The cross-sectional transmission electron microscopy revealed the presence of inclusions of size 10-40 nm in the layers. At room temperature a strong resonant band was observed in the TKE spectra of the InMnAs layers in the energy range of 0.5-2.2 eV. In this band the TKE was comparable in magnitude but opposite in sign to that in the strong ferromagnetic MnAs. The resonant character of the TKE spectra was explained by excitation of surface plasmons in the MnAs nanoclusters embedded in the InMnAs semiconductor host. Modelling the TKE spectra for (InAs)(1 - X):(MnAs)(X) nanocomposites in the effective-medium approximation (Maxwell-Garnett approximation) confirmed the assumption on the plasmon mechanism of the resonant enhancement of the transversal Kerr effect in the InMnAs layers.