George Kioseoglou

Characterization of vapor-phase-grown ZnSe nanoparticles

ZnSe nanoparticles were synthesized by reacting vapors of (CH3)2Zn:N(C2H5)3 and H2Se, diluted in H2, in an opposed flow reactor operating at room temperature and 120 Torr. The particles were collected as random aggregates on silicon substrates and transmission electron microscopy (TEM) grids placed downstream of the reaction zone. Particle characterization using TEM and electron diffraction revealed the presence of polycrystalline nanoparticles with diameter of about 40 nm that were apparently formed from coagulation of smaller nanocrystals with characteristic size of about 4 nm. Raman spectra of the nanoparticles revealed an asymmetrically broadened feature associated with the LO phonon of ZnSe, indicating the presence of smaller single-crystalline grains.

Quantifying electrical spin injection: Component-resolved electroluminescence from spin-polarized light-emitting diodes

The spin-polarized light-emitting diode (spin-LED) is a very effective tool for accurately quantifying electrical spin injection in a model independent manner. We resolve and identify various components which occur in the electroluminescence (EL) spectra of GaAs quantum-well-based spin-LEDs, and examine the circular polarization of each. While a number of components exhibit significant circular polarization, the values do not necessarily reflect the electrical spin injection efficiency. We show that a reliable measure of spin injection efficiency can be obtained only if one takes care to spectroscopically resolve and accurately identify the free exciton or free carrier components of the EL spectrum, and exclude other components.

Vapor Phase Synthesis of II-IV Semiconductor Nanoparticles in a Counterflow Jet Reactor

The vapor-phase synthesis of polycrystalline ZnSe nanoparticles is reported. The particles were grown at room temperature and at a pressure of 125 torr in a counterflow jet reactor and were collected by impact on a Si watler. The precursors used in this study were vapors of (CH 3 ) 2 Zn:[N(C 2 H 5 )3)]2 and H 2 Se gas diluted in hydrogen. These precursors have been used in the past for Metalorganic Vapor Phase Epitaxy (MOVPE) of ZnSe thin films. The particles were characterized by Transmission Electron Microscopy (TEM). electron diffraction. and Raman spectroscopy. The reactor was operated in a continuous, steady-state mode using a gas delivery system that is typical flor MOVPII systems.

Vapor phase synthesis of polycrystalline II-VI semiconductor nanoparticles in a counterflow jet reactor

This paper addresses the vapor-phase synthesis of polycrystalline ZnSe nanoparticles. The particles were grown at room temperature and at a pressure of 125 torr in a counterflow jet reactor and collected by impact on a silicon wafer. The precursors used in this study were vapors of (CH/sub 3/)/sub 2/Zn:[N(C/sub 2/H/sub 5/)/sub 3/]/sub 3/ and H/sub 2/Se gas diluted in hydrogen. These precursors have been used in the past for metalorganic vapor phase epitaxy (MOVPE) of ZnSe thin films. Transmission electron microscopy (TEM), electron diffraction, and Raman spectroscopy were used to characterize the particles. The reactor was operated in a continuous, steady-state mode using a gas delivery system that is typical for MOVPE systems.

INTERNAL TRANSITIONS OF NEUTRAL AND NEGATIVELY CHARGED MAGNETOEXCITONS IN GaAs NANOSTRUCTURES : THE IMPORTANCE OF SYMMETRY

Cyclotron Resonance (CR) of free electrons and holes and internal transitions of their bound complexes have been studied in GaAs/AlGaAs quantum wells in high magnetic fields by Optically Detected Resonance (ODR) spectroscopy. Two nearly degenerate 1s→2p+ internal exciton transitions (IETs), as well as two well-separated 1s→2p- IETs resulting from the two distinct heavy-hole magneto-excitons were observed. Measurements of both electron and hole CR and these IETs in the same sample evidence the predicted consequences of the symmetry of the magneto-exciton Hamiltonian. Extensions of these studies to samples that showed neutral (heavy-hole hhX) as well as negatively charged (X-) exciton photoluminescence-lines have permitted the first observation of internal transitions of X-. Both singlet and triplet transitions of X- were observed, and new physics associated with translational invariance for this interesting three-particle complex was revealed. The observation of electron and hole CR and several IETs in a single sample exemplifies the promise of the ODR technique for the study of semiconductor nanostructures.