Charged exciton emission at 1.3 μ\mum from single InAs quantum dots grown by metalorganic chemical vapor deposition

We have studied the emission properties of self-organized InAs quantum dots (QDs) grown in an InGaAs quantum well by metalorganic chemical vapor deposition. Low-temperature photoluminescence spectroscopy shows emission from single QDs around 1300 nm; we clearly observe the formation of neutral and charged exciton and biexciton states, and we obtain a biexciton binding energy of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV, indicating strong confinement.Comment: 3 pages, 3 figures, submitted AP

Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets

We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05 films to their magnetic properties. The formation of ferromagnetic nanometer sized inclusions in a defect free Ge matrix fabricated by low temperature molecular beam epitaxy is observed down to substrate temperatures T_S as low as 70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount of these precipitates decreases with decreasing T_S. Magnetometry of the films containing precipitates reveals distinct temperature ranges: Between the characteristic ferromagnetic transition temperature of Mn_5Ge_3 at approximately room temperature and a lower, T_S dependent blocking temperature T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3 precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates with blocked magnetic moments is observed. At the lowest temperatures, the films show features characteristic for a metastable state.Comment: accepted for publication in Phys. Rev. B 74 (01.12.2006). High resolution images ibide