Gallium Nitride Ultraviolet Optical Modulators

In narrower band gap semiconductors researchers have exploited the ability to manipulate the exciton resonance via the Quantum Confined Stark Effect to make a variety of different types of optical modulators at infrared wavelengths. In this thesis, the large exciton binding energy of Gallium Nitride is used as the basis for ultraviolet optical modulators without the need for quantum confinement. A 5x5 array of UV optical modulators at 360 nm was fabricated. The modulators operated in a transverse geometry and consisted of a GaN active layer surrounded by transparent AlGaN insulating and electrical contact layers. The typical thickness of the GaN layer was 0.4 um so the effects of the electric field on the exciton resonance could be directly observed. A hydrogenic model for the bulk exciton was assumed. The applied electric field opposed the attractive coulomb potential between the electron and hole and broadens the exciton resonance. This results in more or less light through the device depending on the spectral position. To understand the magnitude of the applied field within the device structure a 1D Poisson Solver was used. Spontaneous polarization and piezoelectric effects due to lattice strain between the AlGaN and GaN layers were included in the model and were found to have influence on the device at lower operating voltages. In the electric field modulated devices a contrast ratio of about 20 percent was obtained. In thermally modulated devices, at low frequencies less than 200 Hz large shifts in the band edge led to large contrast ratios as expected. The temperature dependence of the device followed the Varshni relationship and allowed the magnitude of the temperature shift to be quantified. At higher frequencies from 1kHz to 120 kHz an optical modulation of ~ 5 percent was readily observed and was attributed to electronic effects. The limitation of 100 kHz was equipment related and it is conjectured that the modulation bandwidth would extend into the MHz.

Author dc:creator

• Oberhofer, Andrew Edward

Advisors dc:contributor.advisor

• Dr. John F. Muth, Committee Chair
• Dr. Richard T. Kuehn, Committee Member
• Dr. Salah M. Bedair, Committee Member
• Dr. Dennis M. Maher, Committee Member
• Dr. Mark Johnson, Committee Member

• ultraviolet
• Gallium Nitride
• electroabsorption
• modulator

Statement dc:rights

• I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.

Dc Identifier Other

etd-08172004-161707

OAI record oai:identifier

https://repository.lib.ncsu.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arepository.lib.ncsu.edu%3A1840.16%2F3607