We have investigated the photoluminescence of Gao SIno 2As quantum wells where the top barrier is defined by the surface of Gao 8Ino 2As layers. The spectra of surface quantum wells are compared to the emission of GaAs/Gao 8Ino 2As/GaAs quantum wells with varying GaAs top barrier thicknesses. Due to the increase of the confinement potential in the surface quantum wells we observe a significant blueshift of the emission line (of about 20 meV) compared to the emission line of quantum wells with a thick semiconductor barrier. The experimentally observed energy shift and line broadening for surface quantum wells as well as the onset of the blueshift for quantum wells with thin top barrier layers can be modeled by assuming a 5-eV electron affinity. For quantum wells with top barrier thicknesses below 10 nm we observe a decrease of the emission intensity due to nonradiative recombination at the surface.Two-dimensional systems such as quantum wells (QW's) have been intensely studied during the last two decades. ' Almost all results were obtained on QW's in which the well and both barrier layers consist of a semiconductor. However, confinement may also be obtained if the barrier is given by the transition between a semiconductor and the vacuum or a surface oxide. In this case a very large discontinuity (typically on the order of several eV) may be realized, given approximately by the electron aftinity of the semiconductor. As a consequence in surface QW's a strong increase of the confinement compared to semiconductor barrier structures is expected. Therefore, a wide variety of basic QW properties should change strongly if a surface QW is formed, e.g. , by removing the top barrier layer of a QW by selective chemical etching. This includes a blueshift of the emission energy and a change of the relevant recombination mechanisms.The understanding of the physical properties of surface QW's is furthermore of interest for the modeling of lateral quantization effects in etched quantum wires and dots. In these structures the lateral barriers are defined by open surfaces ' and in a first approximation the confinement potential should be equivalent to the energy discontinuity realized at the surface of the active layers in surface QW's. Up to now surface quantum wells have been studied mainly in conjunction with passivation effects.For GaAs/Alo &Gao 7As surface quantum wells Moison et al. have observed a rather unexpected shift of the emission line to longer wavelengths compared to structures with thick cap layers. The redshift of the emission was attributed by these authors to an interaction of carriers with surface states.We have studied the optical properties of molecularbeam-epitaxy (MBE) grown Gao sino &As/GaAs QW's as a function of the top barrier thickness. In comparison to Gao sino 2As QW's with a thick semiconductor top barrier layer the surface QW emission occurs at significantly higher energy. By a simple model calculation the increase of the quantization can be attributed to the replacement of the rather small energy di...

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We have studied the influence of the surface on the optical properties of GaInAs/GaAs quantum wells for various top barrier thicknesses. A blue shift of the emission lines up to about 25 meV combined with a line broadening is observed for a 5 nm thick surface quantum well (20% In) without any GaAs coverage. The line broadening as well as the energy shift depend strongly on the quantum well thickness. This can be modeled by assuming a 5 eV vacuum potential at the surface.

We have performed systematical investigations of intermixing effects in In0.53Ga0.47As/InP single quantum wells induced by 30-keV Ar+-ion beam implantation with doses ranging from 1012 to 1014 cm−2 and a subsequent rapid thermal annealing (RTA) at temperatures between 600 and 900 °C. After implantation and RTA at 600 °C we observe a significant increase of the photoluminescence emission energy of about 60 meV in comparison with unimplanted heterostructures, indicating that the intermixing is determined by implantation. For RTA above 850 °C, in contrast, the energetic shifts up to 200 meV observed for the implanted samples are similar to the shift in unimplanted samples, indicating a predominant contribution of thermal interdiffusion. The significant decrease of Ga concentration after interdiffusion is confirmed quantitatively by Raman measurements.

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