Search

The electron mobility limited by spacer layer thickness fluctuation (SLTF) scattering on the two-dimensional electron gas in AlGaAs/GaAs modulation-doped heterostructure is investigated. Although the SLTF scattering and the interface roughness scattering are both induced by the roughness of the AlGaAs/GaAs interface, they are two different scattering mechanisms. The interface roughness will lead to the fluctuation of the distance from the electrons to the ideal interface and the fluctuation of the spacer layer thickness. The former induces the fluctuation of the electron potential, which works as the interface roughness scattering potential. The latter induces the fluctuation of the sheet carrier density in the channel, which causes a fluctuation in the quantization energy level. The quantization energy level fluctuation works as the SLTF scattering potential. Compared with the interface roughness scattering, the results reveal that the SLTF scattering becomes the dominant scattering mechanism when the do...

Intersubband absorption energy shifts in 3-level system stemming from depolarization and excitonlike effects are investigated. Analytically, the expressions we derive present good explanations to the conventional 2-level results and bare potential transition energy results; and numerical results show that they are more exact than the previous studies to describe the 3-level system depolarization and excitonlike shift (DES) character especially for higher carrier density (more than 8 x 10(11) cm(-2)). One interesting detail we find is that the "large blue" DES becomes "slight redshift" in the low doping limit (less than 1.9 x 10(11) cm(-2)), which may be neglected by the previous studies of intersubband transitions. Temperature character of DES in the step well structure is also numerically studied. Finally the above are applied to calculate asymmetric step quantum well structures. The two main functional aspects of terahertz (THz) emitters are discussed and several basic optimizing conditions are considered. By adjusting the well geometry parameters and material composition systematically, some optimized structures which satisfy all of the six conditions are recommended in tables. These optimizations may provide useful references to the design of 3-level-based optically pumping THz emitters.