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Semiconductor optoelectronics delivers an integrated, reliable, and ultrafast solution to the ever-increasing bandwidth demand in information technology (IT). The objective of the current project at Ames Research Center is to develop the capability from first principles of physics to understand, design, and optimize optoelectronic devices, in order to meet the IT needs of NASA and the public. The project posted significant accomplishments in the area of comprehensive semiconductor laser simulation in FY00.
The research has increased knowledge across several fronts by (1) studying in more detail the role of many-body effects, or Coulomb interaction between charged carriers, in a semiconductor laser device; (2) clarifying the role of plasma heating in the operations of lasing devices; and, more important, (3) developing a hydrodynamic model for spatial inhomogeneous semiconductor lasers from first principles of microscopic physics.
Specifically, the following results were achieved. First, the researchers found that a law that is believed to be universal for the semiconductor band-gap shrinkage owing to Coulomb interaction in quasi-two-dimensional quantum wells is rather dimension-dependent, and that many-body effects play a nontrivial part in the accurate description of the device, both quantitatively and qualitatively. Second, plasma heating modifies the lasing operations of the device, such as spatial and temporal modulation of the gain and refractive index profile. This in turn alters laser beam quality and dynamics. Third, spatial inhomogeneity-induced diffusion processes increase the injection threshold current, reduce the lasing efficiency, and adversely influence the dynamical response of the laser when subject to injection current modulation.
These results have been included in the comprehensive simulation code for vertical cavity surface emitting lasers (see fig. 1). The benefit and effect of the research constitutes not only an apparently improved simulation tool for design and optimization, but also a successful step toward the long-term commitment for establishing a microscopic-physics-based benchmark for the optoelectronics industry.
Point of Contact: Jianzhong Li
(650) 604-4410
jianzhng@nas.nasa.gov
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Fig. 1. The carrier-density and temperature dependence of the diffusion coefficients formulated in the hydrodynamic model developed in this project. The results are shown in log-log scale. Insets (in XY scale) show the percentage change in the coefficients as a result of the many-body effects. The solid-line curve is 200 K; the dotted-line curve 300 K; and the dot-dashed curve is 400 K.
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