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

The energy spectrum of cosmic rays beyond the turn-down around 10^17 eV as measured with the surface detector of the Pierre Auger Observatory

We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays

Reconstruction of events recorded with the surface detector of the Pierre Auger Observatory

Cosmic rays arriving at Earth collide with the upper parts of the atmosphere, thereby inducing extensive air showers. When secondary particles from the cascade arrive at the ground, they are measured by surface detector arrays. We describe the methods applied to the measurements of the surface detector of the Pierre Auger Observatory to reconstruct events with zenith angles less than 60o using the timing and signal information recorded using the water-Cherenkov detector stations. In addition, we assess the accuracy of these methods in reconstructing the arrival directions of the primary cosmic ray particles and the sizes of the induced showers