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We have studied the effect of rapid thermal annealing (RTA) on GaInNAs/GaAs quantum wells (QWs) grown by molecular-beam epitaxy using a dc plasma as the N source. It was found that RTA at low temperature (LT, 650 °C) and high temperature (HT, 900 °C) could both improve the QW quality significantly. To clarify the mechanism of quality improvement by RTA, a magnetic field perpendicular to the path of the N plasma flux was applied during the growth of the GaInNAs layers for the sake of comparison. It was found that LT-RTA mainly removed dislocations at interfaces related to the ion bombardment, whereas, HT-RTA further removed dislocations originating from the growth. LT-RTA caused only a slight blueshift of photoluminescence peak wavelength, probably due to defect-assisted interdiffusion of In–Ga at the QW interfaces. The blueshift caused by HT-RTA, on the other hand, was much larger. It is suggested that this is due to the fast defect-assisted diffusion of N–As at the QW interfaces. As defects are removed by annealing, the diffusion of In–Ga at interfaces would be predominant.

One of the few and most complete records of the MDICE (Middle Darriwilian Isotope Carbon Excursion) is herein documented from Baltoscandia. Based on a core section penetrating the condensed Lower–Middle Ordovician succession (~46 m) on the island of Öland, southeastern Sweden, we provide an integrated scheme for carbon isotope chemostratigraphy (313 samples) and conodont biostratigraphy (29 samples) for this period. The carbonate succession in the Tingskullen core records 12 conodont zones and 6 subzones, including the Oepikodus evae, Trapezognathus diprion, Baltoniodus triangularis, B. navis, B. norrlandicus, Lenodus antivariabilis, L. variabilis, Yangtzeplacognathus crassus, Eoplacognathus pseudoplanus (Microzarkodina hagetiana and Microzarkodina ozarkodella subzones), E. suecicus, Pygodus serra (E. foliaceus, E. reclinatus, E. robustus and E. lindstroemi subzones) and Pygodus anserinus zones in ascending order. The δ13Ccarb record reveals an apparently complete record of the MDICE, including a rising limb, a well-defined peak and a falling limb. The anomaly covers a thickness of c. 27 m in the core and spans the Eoplacognathus pseudoplanus, E. suecicus, Pygodus serra and P. anserinus conodont zones. Combined with the new, detailed conodont biostratigraphy, the MDICE in the Tingskullen core can be used for detailed correlation with successions from Baltica, North America, the Argentine Precordillera, South China and North China.

We have studied the growth of GaInNAs by a plasma-assisted molecular-beam epitaxy (MBE). It was found that the N-radicals were incorporated into the epitaxial layer like dopant atoms. In the range of 400–500 °C, the growth temperature (Tg) mainly affected the crystal quality of GaInNAs rather than the N concentration. The N concentration dropped rapidly when Tg exceeded 500 °C. Considering N desorption alone is insufficient to account for the strong falloff of the N concentration with Tg over 500 °C, the effect of thermally-activated N surface segregation must be taken into account. The N concentration was independent of the arsenic pressure and the In concentration in GaInNAs layers, but inversely proportional to the growth rate. Based on the experimental results, a kinetic model including N desorption and surface segregation was developed to analyze quantitatively the N incorporation in MBE growth.

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We have investigated the interband electron transitions in a GaNAs/GaAs single quantum well (QW) by photoluminescence and absorption spectra. The experimental results show that the dominant photoluminescence at low temperature and high excitation intensity originates from transitions within the GaNAs layer. The interband transition energy for QWs with different well widths can be well fitted if a type-II band line up of GaNAs/GaAs QWs is assumed.

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