Thermal and Optical Simulations of Vertical Cavity Surface Emitting Lasers
Ng, Wei-Choon
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Permalink
https://hdl.handle.net/2142/80782
Description
Title
Thermal and Optical Simulations of Vertical Cavity Surface Emitting Lasers
Author(s)
Ng, Wei-Choon
Issue Date
2002
Doctoral Committee Chair(s)
Hess, Karl
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
We have developed a fully self-consistent and coupled electronic-thermal-optical simulator for vertical cavity surface emitting lasers (VCSELs). The lattice temperature model is derived based on carrier transport and the conservation of energy. A novel treatment is applied to model distributed Peltier heat at a heterojunction by use of a Monte Carlo simulation. Peltier heat is found to be a major heat contributor, and it results in a rapid and high temperature rise in the separate confinement heterostructure (SCH) region of the laser diode. Carrier thermal conductivities for materials with high mobilities at high carrier densities must be included to account for additional spreading of the thermal energy. Both scalar and vector optical mode solvers for VCSELs have been developed. The scalar self-consistent effective index method (S-EIM) has been shown to compute accurate resonant wavelength, mode profile, and threshold loss as compared to the vector Green's function method and experimental results. The vector model is based on rigorous mode matching and has been formulated to be efficient both in computation volume and speed. The S-EIM method is subsequently used to show that grading the SCH region differently in oxide-confined VCSELs results in wavelength shifts. These shifts can be attributed to two effects: the inward shift of an effective index step that redefines the lambda cavity confinement boundary, and the reduction of the effective index step leading to relaxed confinement abilities of the lambda cavity. The revised understanding of the physics of resonance in a VCSEL hence allows us to compensate the wavelength shifts appropriately. We have investigated the important self-heating effects of thermal lensing and output light power saturation of oxide-confined VCSELs with our complete simulator. The resonant wavelength shift in thermal lensing has been shown to be caused mainly by the heating of the distributed Bragg reflectors. Possible physical factors causing the thermal rollover have been examined. The Auger recombination process is found to be a main contributor to the thermal rollover in 980 nm oxide-confined VCSELs. We have also achieved a very good match between our simulated results and experimental data.
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