Energy levels and properties of a semiconductor quantum well system: The influence of the surroundings and well parameters
Abstract
The constituent layers of a semiconductor quantum well system were studied systematically and sequentially using various spectroscopic and optoelectronic techniques such as photoluminescence, photoreflectance, photovoltage, electroreflectance, or electroluminescence. Complete single quantum well samples with various well parameters were then studied with the appropriate technique. The purpose of the study was to find how the energy levels (the bound states as well as the continuum states) of the quantum well structure were influenced by the surroundings (such as the cap layer, the buffer or the substrate) and the well parameters. To that effect, the well width and the alloy composition (x) of an In$\sb{\rm x}$Ga$\sb{\rm 1-x}$As/GaAs single quantum well were varied, and the results obtained with samples having different cap thicknesses (the other parameters being kept the same) were compared. A theory predicting the influence on the energy levels of the cap layer thickness was developed, and experimental evidence was found in modulated reflectance measurements which showed spectral oscillations for energies above the barrier. The behavior is explained by deriving the wavefunction of the carriers with energies larger than the barrier (continuum states) taking into account the finite size of the cap layer. It was also found in the sequential study that in luminescence, depending on the excitation used, the substrate can contribute to the response obtained with the complete…
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