Development of ultraviolet nitride-based light emitting diodes

Deep ultraviolet light emitting diodes, with emission wavelengths shorter than 360 nm, have attracted interest due to their potential applications as replacement white light sources, in non-line of sight communication, for chemical and biological weapons detection, medical applications, water purification, and counterfeit detection. Light emitters in this wavelength range require AlGaN based active regions with increasing Al composition as the wavelength is decreased. High Al composition AlGaN based devices have been challenged by difficulty in growth, low electron and hole mobilities, and deep dopant levels resulting in low carrier concentrations. The combination of these factors has resulted in UV optoelectronic devices with quantum efficiency several orders of magnitude lower than their GaN/InGaN based visible counterparts. This work will details studies on alternative selective area growth techniques for dislocation reduction and the development of ultraviolet LEDs ranging from 292–340 nm.; Lateral overgrowth of GaN on patterned Si (111) substrates was developed with the hope of developing seed material for bulk GaN growth. The effect of growth conditions on both the crystallographic wing tilt and crack density in the AlN/GaN films was studied. By controlling the lateral to vertical growth rate at the beginning of lateral overgrowth, the wing tilt can be effectively eliminated. We also demonstrate the first lateral overgrowth of AlN to create low threading dislocation density AlN template layers for optoelectronic device development. Deep UV quantum wells grown on this material were studied with cathodoluminescence to study the effect of dislocations on radiative recombination in deep UV devices.; In addition to work on lateral overgrowth of GaN and AlN, 292, 340 nm LEDs were grown on AlN on sapphire and GaN on sapphire respectively. AlN strain relief interlayers were developed to prevent cracking of the 340 nm AlGaN based LEDs that were grown in tension on GaN. This approach was unrealistic for higher composition, shorter wavelength LEDs necessitating development of the growth of AlN and high aluminum containing AlGaN alloys directly on sapphire. Structural and electrical properties of the LEDs in both wavelength regimes will be presented.