First Principles Study On The Optical Properties Of Semiconductor Saurable Absorber

The all solid-state Q-switched lasers, which composed by adding the Q-switching components to the solid-state lasers, are of great interest because of their wide applications with the advantages of all solid state, small volume and high pump efficiency. For the Q-switched lasers, it is essential to optimize the performance of Q-switching components to achieve many of the desired properties. The semiconductor saturable absorbers have been paid much attention on as passively Q-switching components for the advantages of simple structure, convenient utilization and inexpensive price.In this paper, the electronic structures and the optical properties of GaAs and GaAs1-xBix saturable absorbers are calculated by first-principles investigations.The main study contents and the main innovations of this dissertation include:a) The electronic structure and optical properties of the GaAs saturable absorbers with intrinsic point defects are investigated by first principles calculations. The defect energy levels corresponding to each kind of the intrinsic point defect and their electron occupancy are analyzed from the aspects of band structure and partial density of states. Then the impacts of the native point defects on the optical properties of GaAs saturable absorbers are explored. It can be found that the absorption edge of GaAs crystal with VGa defect, VAs defect or GaAs defect shows more redshifts than that of GaAs crystal with AsGa defect, Gai defect or Asi defect, and the absorption coefficient of the former is larger than the latter in near-infrared range. The dielectric function and the refractive index of GaAs crystal with VGa defect, VAs defect or GaAs defect show redshifts in near-infrared region too. The analysis of the optical properties of GaAs crystal with intrinsic point defects will be helpful in guiding the application of the GaAs crystal as a good saturable absorber.b) Electronic structure and optical properties of ternary GaAs:Bi alloy are investigated by first principles calculations. It is found that the band gap of GaAs1-xBix decreases monotonously with increasing of Bi concentration, resulting in the fundamental absorption edge and main absorption peaks of GaAs1-xBix shift toward lower energy with the increase of Bi content. The optical constants of GaAs1-xBix, such as optical absorption coefficient, refractive index, extinction coefficient and optical conductivity, are greater than those of pure GaAs when x>3.1%but less than those of pure GaAs while x<3.1%, which is primarily decided by Bi-6s, Bi-6p orbitals and Ga-4p, Ga-4s orbitals of conduction bands. Bi doping play an important role in modulation of the static dielectric constant and the static refractive index. These results make GaAs1-xBix a promising material for optoelectronics applications.