Strain-dependent Optical Emission In In1 - Xgaxas/inp Quantum Wells

InGaAs/InP strained-layer modulation -doped quantum wells were studied by photoluminescence. The combination of the built-in strain and the quantum confinement in this system leads to a strong valence band mixing yielding direct and indirect band gap structures. We demonstrate that the optical emission line shape is strongly dependent on the valence band dispersion and it is a good method to distinguish between direct and indirect structures. The application of an external biaxial tensile strain to the samples provides an additional evidence of direct-to-indirect band gap transition in strained heterostructures.641515330111533014Gershoni, D., Vandenberg, J.M., Hamm, R.A., Temkin, H., Panish, M.B., (1987) Phys. Rev. B, 36, p. 1320Gershoni, D., Temkin, H., Vandenberg, J.M., Chu, S.N.G., Hamm, R.A., Panish, M.B., (1988) Phys. Rev. Lett., 60, p. 448Gershoni, D., Temkin, H., Panish, M.B., Hamm, R.A., (1989) Phys. Rev. B, 39, p. 5531Chao, C.Y.-P., Chuang, S.L., (1992) Phys. Rev. B, 46, p. 4110Sugawara, M., Okazaki, N., Fujii, T., Yamazaki, S., (1993) Phys. Rev. B, 48, p. 8102Michler, P., Hangleiter, A., Moritz, A., Fuchs, G., Härle, V., Scholz, F., (1993) Phys. Rev. B, 48, p. 111991Triques, A.L.C., Brum, J.A., (1995) Proceedings of the 22nd International Conference on the Physics of Semiconductors, Vancouver, Canada, 1994, 2, pp. 1328-1331. , edited by D.J. Lockwood (World Scientific)Weihofen, R., Weiser, G., Starck, Ch., Simes, R.J., (1995) Phys. Rev. B, 51, p. 4296Dalfors, J., Lundström, R., Holtz, P.O., Radamson, H.H., Monemar, B., Wallin, J., Landgren, G., (1997) Appl. Phys. Lett., 71, p. 503Hosea, T.J.C., Rowland, G., (1998) Supercond. Sci. Technol., 13, p. 207Tudury, H.A.P., Ribeiro, E., Iikawa, F., Brum, J.A., Bernussi, A.A., Carvalho W., Jr., Gobbi, A., unpublishedBastard, G., Brum, J.A., (1986) IEEE J. Quantum Electron., 22, p. 1625Bastard, G., (1992) Wave Mechanics Applied to Semiconductor Heterostructures, , Les Editions de Physique, ParisBaptizmanskii, V.V., Novak, I.I., Titovets, Yu.F., (1979) Sov. Phys. Solid State, 21, p. 1915Liarokapis, E., Richter, W., (1992) Meas. Sci. Technol., 3, p. 347Thewalt, M.L.W., Harrison, D.A., Reinhart, C.F., Wolk, J.A., Lafontaine, H., (1997) Phys. Rev. Lett., 79, p. 26

Biaxial stress ring applications to magneto-optical studies of semiconductor films

We present a magneto-optical system to study semiconductor heterostructures in the presence of an external biaxial tensile strain. The pressure cell is based on the deflection of a plate (the sample) placed between a sphere and a ring. This externally applied stress is easily controlled and can achieve a deformation of up to similar to0.25% for GaAs films. This device is very useful for band structure study and optical resonance experiments in heterostructures. We also present the application of the device to study the behavior of the magneto-excitons in InP epitaxial layer as a function of the biaxial strain. We observed that the diamagnetic and Zeeman effects in InP films are affected by the biaxial tensile strain. (C) 2004 American Institute of Physics.7561947195

Aharonov-Bohm signature for neutral excitons in type-II quantum dot ensembles

It is commonly believed that the Aharonov-Bohm (AB) effect is a typical feature of the motion of a charged particle interacting with the electromagnetic vector potential. Here we present a magnetophotoluminescence study of type-II InP/GaAs self-assembled quantum dots, unambiguously revealing the Aharonov-Bohm-type oscillations for neutral excitons when the hole ground state changes its angular momentum from lh = 0 to lh = 1, 2, and 3. The hole ring parameters derived from a simple model are in excellent agreement with the structural parameters for this system.Comment: Revised version, 10 pages, 3 figure

Saturation of the filament density of ultrashort intense laser pulses in air

We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm2. Propagating 100TW laser pulses over 42m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the bea

Towards an automatic lidar cirrus cloud retrieval for climate studies

In the present study, a methodology to calculate lidar ratios for distinct cirrus clouds has been implemented for a site located in the Southern Hemisphere. The cirrus cloud lidar data processing has been developed to consider a large cloud variability with the final aim of cirrus cloud monitoring through a robust retrieval process. Among the many features lidar systems can extract for cirrus detection, we highlight: cloud geometrical information and extinction-to-backscatter ratio (also called lidar ratio - LR). LR's can, in general, provide important information on cirrus cloud microphysics due to the presence of ice crystals and their properties such as shape, size, composition and orientation of particles and their effect on LR values. Conditions for LR calculations and their resulting uncertainty have been improved as their analysis requires identifying cirrus cloud stationary periods through the use of a specific statistical approach well-established in the literature and employed here with good results, allowing for the study of specific cases with multi-layer cirrus cloud occurrence. The results from the measurements taken in the region of the Metropolitan City of São Paulo - MSP have been used to implement and test the methodology developed herein. In addition to the geometrical parameters extracted, improved values of LR's were calculated and showed significantly different values for the different layers inspected, varying between 19 ± 01 sr and 74 ± 13 sr. This large value interval allowed us to indirectly verify the presence of different ice crystal sizes and shapes and those associated with different air mass sources for the cirrus cloud formation

Influence of pulse duration, energy, and focusing on laser-assisted water condensation

We investigate the influence of laser parameters on laser-assisted watercondensation in the atmosphere. Pulse energy is the most critical parameter. Nanoparticle generation depends linearly on energy beyond the filamentation threshold. Shorter pulses are more efficient than longer ones with saturation at ∼1.5 ps. Multifilamenting beams appear more efficient than strongly focused ones in triggering the condensation and growth of submicronic particles, while polarization has a negligible influence on the process. The data suggest that the initiation of laser-assisted condensation relies on the photodissociation of the air molecules rather than on their photoionizatio

Optical Properties of Type-I and II Quantum Dots

This paper focuses on recent results on the optical properties of self-assembled quantum dots involving type-I InGaAs/GaAs and type-II InP/GaAs interfaces. In the first part, we focus on the InGaAs/GaAs quantum dots, that were used to study the influence of a two-dimensional electron gas on the optical emission of single quantum dots. In the second part, we present the results on type-II InP/GaAs quantum dots. In this system, we observed an experimental evidence indicating that the model used to interpret the blue shift of the type-II quantum well optical emission cannot be applied to type-II quantum dots