Photoluminescence ͑PL͒ spectroscopy and atomic-force microscopy ͑AFM͒ were used to investigate the size evolution of InAs quantum dots on GaAs͑001͒ as a function of the amount of InAs material. Different families of islands were observed in the AFM images and unambiguously identified in the PL spectra, together with the signal of the wetting layer. PL measurements carried out at low and intermediate temperatures showed a thermal carrier redistribution among dots belonging to different families. The physical origin of this behavior is explained in terms of the different temperature dependence of the carrier-capture rate into the quantum dots. At high temperatures, an enhancement of the total PL-integrated intensity of the largest-sized quantum dots was attributed to the increase of diffusivity of the photogenerated carriers inside the wetting layer.
Magnetotransport measurements on bilayer electron systems reveal repeated reentrance of the resistance minima at filling factors =4N + 1 and =4N + 3, where N is the Landau index number, in the tilted magnetic field. At high filling factors, the Shubnikov-de Haas oscillations exhibit beating effects at certain tilt angles. We attribute such behavior to oscillations of the tunneling gap due to Aharonov-Bohm interference effect between cyclotron orbits in different layers. The interplay between quantum and quasiclassical regimes is established.
Mn ions were implanted in p-type cubic GaN at doses from 0.6 to 2.4×1016cm−2 at 200 keV energy. A 200-nm-thick epitaxial layer, grown by molecular beam epitaxy on GaAs(001) substrate, is used for the Mn implantation. The Mn implanted samples were subjected to an annealing at 950 °C for 1–5 min. The structural quality of the samples was investigated by high resolution x-ray diffraction and Raman spectroscopy. The annealing procedure leads to a significant increasing of the crystalline quality of the samples. Hysteresis loops were observed for all cubic GaMnN annealed samples and ferromagnetism was detected up to room temperature.
We have studied the quantum Hall effect in parabolic Al x Ga 1−x As and square GaAs quantum wells with two occupied subbands in magnetic fields B tilted by an angle ⌰ with respect to the normal to the sample. We built the density-magnetic field n s -B and angle-magnetic field ⌰-B topological diagrams for the longitudinal resistivity xx and observed that the latter shows a similarity with a simulation based on a single-particle harmonic potential approximation.
A missing factor cos͑͒ should be included in Eq. ͑2͒. The correct expression isDespite this, all the calculations in the article were done with this correct formula.
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