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A study of the bandgap character of compressively strained GeSn0.060-0.091/Ge(001) quantum wells grown by molecular beam epitaxy is reported. The built-in strain in GeSn wells leads to an increased separation between L and Γ conduction band minima. The prevalent indirect interband transitions in GeSn were probed by photoluminescence spectroscopy. As a result we could simulate the L-valley bowing parameter in GeSn alloys, bL = 0.80 ± 0.06 eV at 10 K. From this we conclude that even compressively strained GeSn/Ge(001) alloys could become direct band gap semiconductors at the Sn-fraction higher than 17.0 at. %.

Metalorganic chemical vapor deposition of GaAs-based laser diodes, using self-organized InGaAs quantum dots ͑QDs͒, emitting at Ͼ1.24 m is demonstrated. The environment-friendly alternative precursor tertiarybutylarsine is used as a substitute for arsenic hydride. The active region contains ten closely stacked InGaAs QD layers embedded in a GaAs matrix. Lasing emission at such long wavelengths was achieved by overgrowing the In 0.65 Ga 0.35 As QDs with a thin In 0.2 Ga 0.8 As film. The application of an in situ annealing step leading to the evaporation of plastically relaxed defect clusters is shown to be decisive for the laser performance. A transparency current density of 7.2 A/cm 2 per QD layer and an internal quantum efficiency of 75% were achieved at room temperature.

We report on the synthesis of a novel optoelectronic material, Sn-rich Ge1–x Sn x nanocrystals in a Ge matrix. The nanocrystals have been formed after annealing of a metastable Ge-rich Ge1–y Sn y film, which was embedded in the Ge matrix. Electron microscopy investigations have revealed that these nanocrystals possess two lattice types: (i) a diamondlike cubic structure with a high Sn fraction (x > 0.5) and (ii) an ordered zincblende structure (x = 0.5).

The photoluminescence ͑PL͒ of self-organized InAs/ GaAs quantum dots ͑QD's͒ shows a decomposition into a set of eight rather narrow lines upon antimony-surfactant mediated growth. This decomposition results from a shell-like growth mode, which means a discrete variation of the QD size in monolayer steps. Based on the PL monolayer splitting, indicative of structurally and chemically well-defined upper interfaces, structural and optical properties can be correlated much more in detail than previously possible for strongly broadened QD ensembles. A comparison of the spectral positions to predictions of eight-band k•p/ configuration interaction model calculations for truncated pyramidal InAs/ GaAs QD's yields excellent agreement only for the shell-like QD growth mode.