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p-side-down, single heterostructure n-InGaN/p-GaN light emitting diodes grown by molecular beam epitaxy exhibited stable peak emission wavelengths as long as 550 nm for current densities in excess of 100 A/cm2, and minimal efficiency droop up to 150 A/cm2 without the use of an electron blocking layer. This behavior is consistent with the formation of a two-dimensional hole gas in the n-InGaN layer and a higher barrier to electron overflow in the conduction band due to the negative polarization charge at the n-InGaN/p-GaN interface.

The incorporation of nanometer scale compositional inhomogeneities in AlGaN has a great promise for improving the performance of UV light emitting diodes based on these materials by suppressing nonradiative recombination associated with dislocations. In this article, the authors report on the growth and characterization of AlGaN containing nanometer scale compositional inhomogeneity (NCI-AlGaN) alloys deposited by plasma-assisted molecular beam epitaxy. Growth under N-limited and nearly stoichiometric growth is observed to enhance the photoluminescence intensity in AlGaN alloys by promoting the spontaneous formation of these NCI regions. This is attributed to the lower adatom mobility of group III and N species on the AlGaN layer surface under these conditions as well as the formation of beneficial surface faceting.

While it is well known that high quality III–nitride material is deposited by plasma-assisted molecular beam epitaxy (PA-MBE) only under III-rich conditions, the extent of III-flux required for optimal film growth is unclear. In this article, we focus on the dependence of the optical properties of the material on the III/V flux ratio. Specifically, we report on the photoluminescence (PL) intensity and the lifetime of photogenerated carriers in homoepitaxially grown GaN films, deposited under Ga-rich conditions, as a function of the Ga flux employed during growth. The samples investigated consist of ∼1.2 μm thick GaN films deposited homoepitaxially on ∼85 μm thick GaN templates grown by the hydride vapor phase epitaxy method. The films were deposited under Ga-rich conditions but without the formation of metal droplets. The Ga flux was varied from 0.89 to 1.0×10−6 Torr while the N-plasma conditions (300 W, 0.6 sccm) were held constant. The intensity of the room temperature PL measured for films grown under ...

High reflectivity and crack-free ultraviolet distributed Bragg reflectors (DBRs), based on AlGaN/AlN quarter-wave layers, have been designed and grown on (0001) sapphire by plasma-assisted molecular beam epitaxy. To minimize the tensile stress and thus prevent nucleation and propagation of cracks in the DBRs, the substrate was coated first with an AlN film, of thickness approximately equal to the total thickness of all the AlN layers in the epitaxially grown DBR structure. In such a configuration the AlN layers are stress-free, while the AlGaN layers are under compressive stress. Peak reflectivity higher than 99% was obtained in all samples. The design calculations and simulations of measured reflectivity data were performed using the transmission matrix method. The measured reflectivity spectra have a bandwidth of around 20% smaller than the simulated spectra, a result attributed to a combination of changes of the thickness and variations in the Al content in the quarter-wave layers.