Design and fabrication of ultraviolet light emitting diodes
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Ultraviolet Light Emitting Diodes (UV-LEDs) are showing a lot of promise in various fields such as chemistry, biology, environmental science and optics. UV-LEDs offer sharper peak profile, lower power consumption, and longer life time over conventional UV lamps. This thesis deals with the design and fabrication of UV-LEDs using alloys of AlGaN. The diodes were composed of a p-n junction of AlGaN alloy with concentration of AIN approximately equal to 65%. The active layer consisted of a multi-quantum-wells structure with three quantum wells. The wells and barriers were composed of AlGaN alloys with concentration of AIN approximately equal to 50% in wells and 60% in the barriers. A carrier blocking layer of AIN of thickness 5nm was grown on both sides of the active layer in one of the samples, and its effects on the device characteristics were investigated. Separate samples of n and p type AlxGai.xN alloy were subjected to Hall measurements and C-V analysis to ascertain their electrical characteristics and to study the effects of varying AIN concentration in the alloy. The MBE grown p-« junction was subjected to SEM analysis to verify the thicknesses of various layers, and cathodoluminescence to evaluate the crystalline quality of the sample. It was then mesa etched with Cla/Ar plasma to be able to provide electrical contacts to the n side of the diode. Electrical contacts were formed to the p and n sides, making use of photolithography, e-beam metal evaporator, oxygen plasma cleaning, wet etching and lift off processes. The LEDs thus fabricated were tested for electroluminescence, I-V characteristics and power characteristics.