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Growth and point defect control of AlGaN for UV laser diodes

Thursday March 12, 2020
11:30 am


 Presenter:  Dr. Ramón Collazo, WideBandgaps Laboratory, Department of Materials Science and Engineering, N C State
 Series:  OSE Seminars
 Abstract:  The AlGaN material system offers unique opportunities to develop next generation UV lasers with emission ranging 210 – 350 nm. Such devices find direct and immediate uses in health care, bio-defense and other commercial and defense applications. However, despite many efforts, only a few examples of electrically injected laser diodes with emission wavelength < 350 nm have been demonstrated. Among others, challenges for these devices include low doping and low carrier injection efficiency, absorbing layers and defects, and non-ohmic contacts. Here, we present recent advances in the growth and fabrication of UV laser diodes on single crystal AlN and GaN substrates focusing on necessary point defect control and relaxation schemes during growth by MOCVD. Point defect incorporation in Al/GaN is dependent on the defect formation energy and hence on associated chemical potentials and the Fermi level. We demonstrate a systematic point defect control by employing the defect formation energy as tool by (a) chemical potential control and (b) Fermi level control. In addition, AlGaN growth on AlN is under compression but on GaN is under tension. We demonstrate specific relaxation schemes to avoid AlGaN cracking for growth of high Ga-content AlGaN on GaN substrates. In terms of UV laser fabrication, all steps needed to achieve electrically injected UV lasing will be described. First, it is shown that the MOCVD growth on AlN substrates results in high quality AlGaN layer with low defect concentration and excellent doping capabilities after implementation of the point defect control schemes. Next, design of the active region (MQW) is discussed and low threshold optically pumped lasing is demonstrated. Considering simulation results, the design and growth of a complete UV laser diode is shown and fabrication challenges are analyzed. Finally, we present electrical data and electroluminescence spectra from fabricated diodes and discuss the challenges that need to be addressed to realize electrically injected UV laser diodes.
 Location:  Room 101, Center for High Tech Materials

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