Device Processing Studies of Aluminum-Rich AlGaN Superlattices

Texas Tech University, Lubbock TX

Investigators

Abstract

The PIs will investigate critical issues in growth and processing of deep ultraviolet light emitting diodes (LEDs). The wavelength range of interest is from 280 to 240 nm, and will be reached using AlN/AlxGa1-xN superlattices (SLs) with nanometer periods (1.25 - 2.25 nm). Their specific goals to advance from growth to device processing are: 1. High p-type carrier concentrations are difficult to obtain due to the increasing hole activation energy in AlxGa1-xN with increasing x. Experiments will address the optimization of energy gap while reaching high carrier concentrations. 2. LED performance relies on the ability to form Ohmic contacts to p-type and n-type materials. The situation for these materials is complicated by the presence of native oxides which form upon exposure to air. They propose to study and improve contact resistance for these Al-rich surfaces by controlling air exposure between growth and metal deposition. 3. Producing mesa device structures relies on plasma etching. Their preliminary work shows the AlN/AlGaN SL etch rates to depend on composition and doping. Furthermore, they find a delay in the onset of etching, once plasma conditions are established, which we attribute to native oxide formation. They will study these effects for controlling the etch of device structures. The influence of etching conditions on their ability to form Ohmic contacts needs to be understood. They propose systematic experiments to address these important issues. Intellectual Merit. This fundamental research addresses must be carried out to produce deep UV LEDs. Advanced growth methods will be developed to control energy gaps and material quality in AlN-rich materials. Implications for doping will be studied, and processing issues of electrical contacts and plasma etching addressed. The final goal is to demonstrate a deep UV LED operating in the 240 nm range. The application of high power LEDs in the deep UV range extends to biological, chemical, and environmental sensing, thus relating to current national security issues. Broader Impact. The interdisciplinary research setting combines physics, materials science, and advanced engineering. This provides excellent opportunities in these areas for graduate and undergraduates students from science and engineering, developing important technical, team, and leadership abilities. They will continue their involvement in Texas Tech, regional university, and local outreach and recruitment activities. These efforts strive to increase the number of qualified students in their University research community, interest young students in science and engineering careers, and recruit from the regional community of students rich in underrepresented talent.