686769 event 1765206299 1765304953 <![CDATA[Ph.D. Proposal Oral Exam - Alexandra Dolgashev]]> Title:  MOCVD III-Nitride Optoelectronic Devices: Optimizing Growth, Fabrication, and Design of GaN and AlGaN APDs and Micro LEDs

Committee:

Dr. Dupuis, Advisor

Dr. Yoder, Chair

Dr. Otte

]]> The objective of the proposed research is to develop III-nitride ultraviolet (UV) avalanche photodiodes (APDs) and micro light emitting diode (µLED) arrays using metalorganic chemical vapor deposition. The low noise, robustness, and efficiency capabilities of gallium nitride will be explored by developing and improving the epitaxial structure and design of APDs for single UV photon detection and UV µLED for integration into high density arrays. To improve the leakage current present at high bias in APDs, shallow bevel two step p-type doped p-i-n APDs were grown, fabricated and characterized. Due to the improvements in responsivity gained with this epitaxial structure, further design and fabrication elements were studied by varying depth, mesa size, different contacts, and top passivation layers. A new method of creating the bevel mesa using greyscale optical lithography was also studied and implemented to improve the uniformity of the bevel mesa. After determining the optimal mesa depth and passivation, further passivation studies are planned to be done on the same structure and will be applied to three different GaN APD structures grown with different unintentionally doped (uid) impurity compositions to minimize leakage current. Along with further work on GaN, this study is also planned to be expanded to high aluminum composition AlGaN APDs in the next year. Micro ultraviolet LED arrays with 24-48µm pitch have many uniformity, fabrication, and growth challenges that need to be explored. To test the growth and fabrication viability of the array, different epitaxial LED structures were tested and fabricated into LEDs of various sizes. After optimizing the light output power and establishing a positive correlation between smaller mesa dimensions and higher efficiency, the next steps are outlined with a focus on further material growth and device optimization for array integration.

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