Systematic optimization of quantum junction colloidal quantum dot solar cells Appl. Phys. Lett. 101, 151112 (2012) Quantum-confined stark effect in localized luminescent centers within InGaN/GaN quantum-well based light emitting diodes Appl. Phys. Lett. 101, 121919 (2012) Performance and polarization effects in (112) long wavelength light emitting diodes grown on stress relaxed InGaN buffer layers Appl. Phys. Lett. 101, 121106 (2012) Optical absorptions in AlxGa1−xAs/GaAs quantum well for solar energy application J. Appl. Phys. 112, 054314 (2012) Analyzing the physical properties of InGaN multiple quantum well light emitting diodes from nano scale structure 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 ͑DES͒ character especially for higher carrier density ͑more than 8 ϫ 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 1.9ϫ 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 ͑THz͒ 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.
We have investigated experimentally and theoretically the influence of the quantum confinement effect on internal transitions of shallow beryllium acceptors in both bulk GaAs and a series of delta-doped GaAs/AlAs multiple quantum well samples with well width ranging from 30 to 200 Å. A series of beryllium delta-doped GaAs/AlAs multiple-quantum wells with the doping at the well centre and a single epilayer of GaAs uniformly Be doped were grown by molecular beam epitaxy. Far-infrared absorptions were measured at 4.2 K for all samples. Three principal absorption lines were observed clearly, which correspond to acceptor state transitions from the ground state 1s 3/2 ( 6 + 7 ) to the three excited odd-parity states 2p 3/2 ( 6 + 7 ), 2p 5/2 ( 6 + 7 ) and 2p 5/2 7 , respectively. The photoluminescence spectra were measured at 4, 20, 40, 80 and 120 K, respectively. The two-hole transition of the acceptor-bound exciton from the ground state, 1S 3/2 ( 6 ), to the excited state, 2S 3/2 ( 6 ), has been clearly observed. A variational principle is presented to obtain the 2p-1s and 2s-1s transition energies of quantum-confined beryllium acceptors as a function of the well width. It is found that the acceptor internal transition energy increases with decreasing quantum-well width, and the experimental results are in good agreement with the theoretical calculation.
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