UV laser diodes
- Degree Grantor:
- University of California, Santa Barbara. Materials
- Degree Supervisor:
- Shuji Nakamura
- Place of Publication:
- [Santa Barbara, Calif.]
- University of California, Santa Barbara
- Creation Date:
- Issued Date:
- Engineering, Electronics and Electrical and Engineering, Materials Science
- Dissertations, Academic and Online resources
- Ph.D.--University of California, Santa Barbara, 2014
There are a wide range of applications for laser diodes operating at wavelengths below 360 nm including sterilization, water purification, chemical detection, and other industrial applications. Despite the clear market and obvious advantages diodes lasers would have over incumbent technologies, commercially available III-Nitride lasers are presently limited to wavelengths greater than 370 nm. Much of the technical difficulty arises from the generation of defects such as cracks and threading dislocations due to misfit strain. The radiative efficiency of GaN/AlGaN based emitters is much more sensitive to threading dislocation density than visible InGaN emitters, resulting in the need for higher quality substrates and films.
With Semipolar GaN substrates we are able to exploit a unique relaxation mechanism that is unavailable for traditional c-plane nitride devices grown on sapphire. This allows for thick, partially relaxed, AlGaN films with defect densities lower than anything previously reported. Using these low defect density AlGaN films we have fabricated lasers in the near UV and demonstrated the potential for much shorter, deep UV devices.
However this same mechanism that allows for these relaxed buffer layers also limits the critical thickness of the waveguide structures, resulting in low optical confinement factors. Exotic waveguide structures such as limited area epitaxy and asymmetric relaxed waveguides can be used to mitigate these issues.
The low quantum efficiency of indium-free active regions on semipolar orientations grown by MOCVD is a serious impediment to short wavelength devices. It is likely the result of the formation of thermodynamically stable facets that causes the reduction in radiative efficiency. Growth by molecular beam epitaxy (MBE) can improve the quantum efficiency of these active regions by kinetically suppressing the formation of these facets.
Electrically injected semipolar (202 1) laser diodes grown on a relaxed AlGaN buffer layers are demonstrated. The lasing wavelength was 384 nm. Reduction in the lasing wavelength was not achieved due to the challenges previously mentioned.
- Physical Description:
- 1 online resource (216 pages)
- UCSB electronic theses and dissertations
- Catalog System Number:
- Dan Haeger, 2014
- In Copyright
- Copyright Holder:
- Dan Haeger
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