Interband Transitions In Quantum Wells Research Articles

Nonlinear Photoexcitation of Heterostructures with Deep Quantum Wells: I. Probabilities of Elementary Processes

The probabilities of different types of optical processes involved in the formation of a photon avalanche in type-I heterostructures with deep quantum wells are calculated. The processes include two-electron transitions with participation of a photon, phototransitions between electronic states of size-quantized subbands and continuum of band states, and two-photon interband transitions in quantum wells. The obtained probabilities will be used in the forthcoming parts of the study for analysis of photon-avalanche kinetics.

Investigation of HgCdTe waveguide structures with quantum wells for long-wavelength stimulated emission

The photoluminescence and stimulated emission during interband transitions in quantum wells based on HgCdTe placed in an insulator waveguide based on a wide-gap CdHgTe alloy are studied. Heterostructures with quantum wells based on HgCdTe are of interest for the development of long-wavelength lasers in the range of 25–60 μm, which is currently unattainable for quantum-cascade lasers. Optimal designs of quantum wells for attainment of long-wavelength stimulated emission under optical pumping are discussed. It is shown that narrow quantum wells from pure HgTe appear to be more promising for long-wavelength lasers in comparison with wide (potential) wells from the alloy due to the suppression of Auger recombination. It is demonstrated that molecular-beam epitaxy makes it possible to obtain structures for the localization of radiation with a wavelength of up to 25 μm at a high growth rate. Stimulated emission is obtained for wavelengths of 14–6 μm with a threshold pump intensity in the range of 100–500 W/cm2 at 20 K.

Size and ternary mixed crystal effects on interband absorption in wurtzite ZnO/MgxZn1-xO quantum wells

Adopting a numerical method of solving self-consistently the Schrödinger equation and Poisson equation, the eigenstates and eigenenergies of electrons (holes) in a two-dimensional electron-hole gas are obtained for wurtzite asymmetric ZnO/MgxZn1-xO single quantum wells (QWs). In our computation, a realistic heterostructure potential is used, in which the influences from energy band bending, material doping and the built-in electric field induced by spontaneous and piezoelectric polarizations are taken into account. Furthermore, based on the Fermi's golden rule, the optical absorptions of electronic interband transitions in QWs, and their size and ternary mixed crystal effects are discussed. The results indicate that the increase of the Mg component in MgxZn1-xO enhances the build-in electric field, which forces electrons (holes) to approach to the left (right) barrier. This causes the interband transition absorption peak to decrease exponentially and to be blue-shifted. For different widths of QWs, the calculated results show that absorption peak decreases and transition energy shows a red shift with the increase of well width. The above conclusions are expected to give a theoretical guidance for improving the opto-electronic properties of materials and devices made of heterostructures with suitable optical absorption spectra and wave lengths.

A laser operating on the interband transitions in quantum wells with coherent electron transport

A new approach to the creation of a quantum cascade laser is suggested, which employs interband transitions in quantum wells with a coherent electron transport. The coherent electron transport is studied based on the simplest two-band Kane model, in which the interaction between states of the conduction and valence bands is described taking into account only states in the light hole subband of the valence band.

Electromagnetically induced transparency of interband transitions in quantum wells

In the presence of a coherent coupling between two electron conduction sub-bands within doped quantum wells, both the Coulomb and light induced electronic renormalizations on electron and hole eigenenergies and eigenstates are studied by employing a generalized density functional approach. The dynamic properties of interband absorption of a probing laser are investigated. Electromagnetically induced transparency in interband transitions and optical switching is shown. The effects on the absorption coefficient due to pump field amplitude, electron area density, inhomogeneous level broadening, and delta -doping layer position are investigated and explained.