The objective of this research is to develop high efficiency (20-30%) deep ultraviolet light emitting diodes. The proposed research has the potential for a strong impact on the environmental and medical sectors, due to specific applications to water / air / food sterilization and for diagnostic and therapeutic uses. Furthermore, the proposed research activities will promote education through the training of students in a variety of disciplines, ranging from growth of semiconductor thin films, device fabrication and characterization, and emerging technologies. To increase the effectiveness and scope of the program, the involvement of undergraduates and high-school interns will be emphasized by taking advantage of several existing channels at Boston University, many of which have a strong focus on the recruitment of underrepresented minorities. The NSF support of this project is justified since it is basic science and the technology it addresses has a large number of societal and educational benefits.
The specific goal is to demonstrate high efficiency (20-30%) deep UV LEDs based on AlGaN alloys grown on p-SiC substrates. This efficiency value is 3 times higher than the best result currently reported in the literature. In order to accomplish this goal long standing problems of low internal quantum efficiency (IQE), low injection efficiency (IE), and low extraction efficiency (EE) will be addressed. The AlGaN structures will be grown on p-SiC substrates, to which they are better lattice matched than the commonly used sapphire substrates. Improvements in IQE will be obtained by growing the active region of the device under a growth mode, which leads to band structure potential fluctuations and thus efficient radiative recombination. The expected IQE value will be 70% or higher. The LED device will be an inverted structure on a degenerately doped p-SiC substrate, which together with polarization assisted injection of holes is expected to lead to IE 50% or higher. A conducting AlGaN-based p-type DBR will be incorporated between the substrate and the active region to prevent absorption in the p-SiC substrate. Furthermore, the inverted structure will allow light extraction from the transparent n-AlGaN side of the device, which can textured for maximum light extraction leading to EE of 70% or higher.
