International audienceWe report on the growth of Al 0.57 Ga 0.43 N/Al 0.38 Ga 0.63 N MQWs grown on a relaxed Al 0.58 Ga 0.42 N buffer on AlN template by Metal Organic Vapor Phase Epitaxy. The MQW structure is designed so that the strain in the quantum wells induced by their lattice mismatch with barriers is sufficient to enhance TE polarized emission (E-field ⊥ c). A 630-nm thick relaxed Al 0.58 Ga 0.42 N buffer grown on AlN template serves as a pseudo-substrate to release the strain in the barriers and to avoid related defects or composition fluctuation in the active region. Thin (< 2 nm) quantum wells allow preservation of the overlapping of electron and hole wavefunctions considering the strong quantum-confined Stark effect in AlGaN-based MQW structures. Scanning transmission electron microscopy (STEM) coupled to energy-dispersive X-ray spectroscopy (EDX) analysis is used to optimize the growth conditions and to determine the composition of wells and barriers. Optical characterizations of the grown structure reveal a well-defined band-edge emission peak at 285 nm. Based on macro-transmission measurements and simulations, the absorption coefficient of the wells is estimated to be 3 × 10 5 cm −1 (E-field ⊥ c), attesting that the oscillator strength is preserved for these AlGaN MQWs with high Al content, which is promising for efficient surface-emitting devices in the deep ultra-violet (DUV) region

GaN epitaxial layers with different crystalline quality grown on sapphire substrates by metalorganic chemical vapor deposition are investigated using time-resolved photoluminescence at 300 K. It is found that the time-dependent photoluminescence of low-quality GaN decays faster than that of the high-quality GaN films. The time constants for the dual-exponential decay of the photoluminescence are calculated to be 50 and 250 ps for high-quality undoped GaN and 30 ps for low-quality undoped GaN. For high-quality Si-doped GaN, time constants of 150 and 740 ps are extracted while corresponding time constants of 40 and 200 ps are measured for low-quality Si-doped GaN. We believe that the time constant of 740 ps measured for our high-quality Si-doped GaN is the longest ever reported for thin GaN/sapphire films.

The implantation of Si ions into undoped high-resistivity GaN films is of interest for the realization of high-performance digital and monolithic microwave integrated circuits. We report the effect of postimplant annealing conditions on the electrical, optical, and surface morphology of Si ion-implanted GaN films. We demonstrate high activation efficiencies for low-dose Si implants into unintentionally doped GaN/sapphire heteroepitaxial films. The Si ions were implanted through an epitaxial AlN cap layer at 100 keV and a dose ∼5×1014 cm−2. Samples were subsequently annealed in an open-tube furnace for various times and temperatures. The postanneal electrical activation is correlated with the surface morphology of the film after annealing. The samples annealed at 1150 °C in N2 for 5 min. exhibited a smooth surface morphology and a sheet electron concentration ns∼6.8×1013 cm−2.

We report the growth of high-quality GaN heteroepitaxial films on (0001) sapphire substrates by low-pressure metalorganic chemical vapor deposition. These films have exhibited narrow x-ray-diffraction rocking curves with full-width-at-half-maximum values as low as ΔΘ∼38 arc sec. These are the narrowest x-ray-diffraction rocking curve linewidths reported to date for any III-V nitride film. Electrical and optical measurements further indicate the samples to be of high quality.

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