Theoretical Model for Optical Gain of Germanium & Electronic and Optical Properties of Graphene & Electronic and Optical Properties of Graphene
Date Issued
2009
Date
2009
Author(s)
Chen, Chih-Yuan
Abstract
There are two topics included in this thesis. In the first topic, we develop a theoretical model for optical gain of Germanium (Ge) to investigate the possibility for Ge to be applied into the laser devices. Optical gains of relaxed and tensile strained Ge are all simulated using many reasonable material parameters. Our simulation results show that the optical gain can be much enhanced by biaxial tensile strain, and making the laser application possible for Ge. However, excessively large tensile strain would also cause the red shift of gain spectrum and eliminate the gain at 1550nm. The optimum strain condition for Ge 1550nm laser is 1.25% tensile strain and the minimum threshold injected carrier density is 4.35x1019 cm-3.n the second topic, we discuss the electronic and optical properties of graphene and graphene nano ribbon (GNR). The nearest-neighbor tight binding approximation is used to calculate the band structures for the systems. Based on these band structures, the absorption spectra can be obtained with the k-space gradient of the tight-binding Hamiltonian. The issue of the orientation effect in GNR is also discussed. Due to the stronger and stronger edge state, the band gap of GNR shrinks at higher orientation angles. Our calculation result shows the subtle reaction of edge state to the changing of the orientation. Even an orientation as small as 6.6? can induce a very strong edge state.
Subjects
Optical gain
Germanium lasers
indirect band gap
tensile strain
graphene nano ribbon
tight binding
edge state
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-R96943045-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):74d0f27d8428c207f12c091befc449b6