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AlGaN based deep ultraviolet light emitting diodes (DUV LEDs) are key components in systems for air, water, and food purification and germicidal applications. Because of the heteroepitaxial growth of the DUV LED epilayers on sapphire, they have a large number of dislocations that invariably leads to a reduction of quantum efficiency and lifetime degradation. In this paper, we present our recent work at developing DUV LEDs with different device geometries, which includes a new micro-pixel electrode arrangement. This arrangement was used to study mechanisms responsible for their degradation. The micro-pixel device geometry with some new packaging schemes led to DUV LEDs with emission at 280 nm and lifetimes well in excess of 3000 hours. In this paper experimental details and the results of our study are presented.

An in situ Auger probe (AP) is employed to monitor changes in growth surface chemistry of the component elements of Terfenol-D, a completely miscible alloy of DyFe2 and TbFe2. The AP's surface sensitivity is quantified by depositing Dy onto a layer of Tb in 0.01 monolayer increments. The AP is able to distinguish surface coverage changes as small as 2% of a monolayer when elements with similar Auger spectra are used. The AP also allowed the identification of oxygen contamination in the system. Additionally, the glancing angle incidence primary electrons result in enhanced surface sensitivity compared to a more traditional Auger electrons spectroscopy configuration.

InN, high indium content InGaN, and Mg-doped InGaN were grown by metal modulated epitaxy (MME). Transient reflection high-energy electron diffraction intensities were analyzed during the growth of InN and found to be similar to that previously reported for GaN and AlN. The x-ray diffraction rocking curve and background electron concentration of InN grown by MME were found to be respectable in comparison to recent reports in literature. InGaN alloys grown by MME were also investigated, and a method for detecting indium surface segregation was demonstrated. It was found that the shutter modulation scheme could be modified to prevent phase separation by indium surface segregation, and a range of single-phase InGaN samples with indium contents throughout the miscibility gap were grown. Using the discovered method of suppressing phase separation, several p-InxGa1 − xN samples were grown with indium contents from x = 0 to 0.22. A maximum hole concentration of 2.4 × 1019 cm−3 was detected by Hall effect characterization, demonstrating feasibility of these p-InGaN layers for use in several device applications.

Highly p-type GaN films with hole concentrations exceeding 6 × 1019 cm−3 grown by metal-modulated epitaxy are electrically characterized. Temperature-dependent Hall effect measurements at cryogenic temperatures reveal minimal carrier freeze-out in highly doped samples, while less heavily doped samples exhibited high resistivity and donor-compensated conductivity as is traditionally observed. Effective activation energies as low as 43 meV were extracted, and a maximum Mg activation efficiency of 52% was found. In addition, the effective activation energy was found to be negatively correlated to the hole concentration. These results indicate the onset of the Mott-Insulator transition leading to impurity band conduction.

The growth of InGaN alloys via Metal-Modulated Epitaxy has been investigated. Transient reflection high-energy electron diffraction intensities for several modulation schemes during the growth of 20% InGaN were analyzed, and signatures associated with the accumulation, consumption, and segregation of excess metal adlayers were identified. A model for shuttered, metal-rich growth of InGaN was then developed, and a mechanism for indium surface segregation was elucidated. It was found that indium surface segregation only occurs after a threshold of excess metal is accumulated, and a method of quantifying this indium surface segregation onset dose is presented. The onset dose of surface segregation was found to be indium-composition dependent and between 1 and 2 monolayers of excess metal. Below this surface threshold off excess metal, metal-rich growth can occur without indium surface segregation. Since at least 2 monolayers of excess metal will accumulate in the case of metal-rich, unshuttered growth of InG...

The surface kinetics of InGaN alloys grown via metal-modulated epitaxy (MME) are explored in combination with transient reflection high-energy electron diffraction intensities. A method for monitoring and controlling indium segregation in situ is demonstrated. It is found that indium segregation is more accurately associated with the quantity of excess adsorbed metal, rather than the metal-rich growth regime in general. A modified form of MME is developed in which the excess metal dose is managed via shuttered growth, and high-quality InGaN films throughout the miscibility gap are grown.