The optical properties of GaN thin films grown on sapphire substrates by low-pressure metal organic chemical vapor deposition were investigated by variable-angle spectroscopic ellipsometry. Accurate refractive indices (n, k) below, through, and above the fundamental bandgap of GaN in the spectra range of 1.5 to 3.8 eV (330 to 830 nm) were determined by using a parametric semiconductor model that took the surface roughness effect into account. The fundamental bandgap energy (3.41 eV) of GaN determined by the model was exactly the same as that obtained from an optical transmission experiment using the same sample. The high-frequency dielectric constant ε ∞ (=5.2) of GaN for (E⊥c) obtained from the ellipsometric measurement was also in excellent agreement with the experimental value of 5.2±0.1 (E⊥c) from the IR reflectivity measurements.

Photoluminescence and photoreflectance study of InGaAs/AlAsSb quantum wells grown by molecular-beam epitaxy Mechanism for low-temperature photoluminescence in GaNAs/GaAs structures grown by molecular-beam epitaxy Appl. Phys. Lett. 75, 501 (1999); 10.1063/1.124429Self-organized InAs/GaAs quantum dots grown by gas source molecular beam epitaxy

We have investigated the influence of growth interruption when group-III sources are temporarily shut off, and that of the number of quantum-well (QW) layers, on the crystalline quality of InGaN/GaN QW structures grown by metalorganic vapor phase epitaxy. Atomic force microscopy measurements revealed that the size of the pits on the QW surface increased dramatically as the interruption time increased. Through transmission electron microscopy and energy dispersive x-ray microanalysis, we found that the pit formation due to growth interruption induces fluctuation in the In composition around the pits in the QW structure, which leads to significant variation in the growth rate as the number of QW layers increases.

Strain effects and atomic arrangements of 60° and 90° dislocations near the ZnTe/GaAs heterointerface Appl.Local interface composition and extended defect density in ZnSe/GaAs(001) and ZnSe/In 0.04 Ga 0.96 As (001) heterojunctions J.The lifetime of II-VI-based blue-green laser diodes on GaAs substrates is limited by rapid degradation in the active layers. This degradation has been observed as dark defects in the active layer during the laser operation, where defects occurred due to stacking faults that originated from the Ga 2 Se 3 compounds at the ZnSe/GaAs interface. The reported value of the density of stacking faults of the II-VI lasers was in the order of 10 5 cm Ϫ2 . To extend the lifetime, surface treatment of the GaAs substrate and control of the interface reaction are necessary. We investigated a new treatment technique using hydrogen-radical and Zn/As fluxes. We fabricated ZnSe-based double-hetero ͑DH͒ structures on a treated GaAs substrate and measured the density of dark defects in the light emitter area by electroluminescence microscopy. Chemical bonds at the interface were evaluated by x-ray photoelectron spectroscopy. A dark defect density of less than 10 5 cm Ϫ2 was obtained when the As-terminated GaAs surface was Zn treated. The Zn treatment prevented the formation of the Ga 2 Se 3 layers. When we alternated the exposure between Zn and As fluxes, excess ZnAs x interfacial layers were formed and the quality of the DH structure was unacceptable. However, hydrogen-radical exposure before and during the Zn/As treatment effectively removed the excess ZnAs x compounds, and the density of dark defects fell to 2ϫ10 4 cm Ϫ2 .

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