The optoelectronic characteristics of self-assembled InAs quantum dots ͑QDs͒ with strain-reduced layers ͑SRLs͒ were investigated using photoluminescence ͑PL͒ spectroscopy. Various SRLs that combine In 0.14 Al 0.86 As and In 0.14 Ga 0.86 As with the same total thickness were examined to ascertain their confining effect on carriers in InAs QDs. The emission wavelength is blueshifted as the thickness of InAlAs is increased. The energy separation between the ground state and the first excited state of QDs with InAlAs SRLs greatly exceeds that of QDs with InGaAs SRLs. Atomic force microscopic images and PL spectra of the QD samples demonstrated that high-quality InAs QDs with long emission wavelengths and a large energy separation can be generated by growing a low-temperature, thin InAlAs SRL onto self-assembled QDs.

The electronic structures of III–V-nitride semiconductors, including InGaAsN, GaAsN, and InAsN grown by molecular beam epitaxy, were investigated by high-resolution x-ray photoelectron spectroscopy using synchrotron radiation beam and low energy Ar+ sputtering. The N(1s) core-level photoelectron spectra show a single peak with a binding energy (Eb)∼398.0 eV of N–Ga bonding for GaAsN sample. For the InAsN samples, a single N(1s) peak at Eb∼397.0 eV of N–In bonding is observed. For the InGaAsN samples, the N(1s) spectra exhibit two peaks with a major component corresponding to N–In bonding, and a minor one to N–Ga bonding. The integrated N(1s) intensity of N–In bonding has a higher value than that of N–Ga bonding, in spite of the lower mole fraction of In for the InGaAsN sample. The data indicate that N has a bonding configuration with In-rich nearest neighbors in the InGaAsN samples.

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Stacking of InAs/InGaAs/GaAs QDs up to 5 layers has been developed to realize ground state lasing with noticeable output power in the laser diodes with broad and low contrast wave guide (0.6 µm Al 0.3 Ga 0.7 As/GaAs). Lasers emitting at 1310 nm were grown by molecular beam epitaxy and processed into 5 µm wide ridge waveguide diodes. Single lateral mode continuous wave operation was achieved in a 3 mm long diode with as-cleaved facets. The threshold current of 26 mA (J th = 173 A/cm 2 ), a slope efficiency of 0.43 W/A (η dif = 45%), a characteristic temperature of 85 K, a vertical beam divergence of 45°, and I−V characteristics with turn-on voltages of 1.0 V and series resistance of 1.5 × 10 −4 Ω cm 2 were realized in one device simultaneously.

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