domingo, 25 de julio de 2010

Modulation Spectroscopy and Optical Excitation of Band-to- Band Transitions in Quantum-Well Structures

In QW structures, the electron and hole confinement energies as well as their subband structures are sensitive functions of the electron and hole masses. These physical properties are commonly retrieved from band-to-band optical transitions between the CB and the VB by using photoluminescence excitation (PLE), photovoltaic measurements, ora variant of modulation spectroscopy. In the latter, instead of measuring optical reflectance (or transmittance), the spectral response modified by a repetitive perturbation (e.g., light, an electric field, a heat pulse, or stress) is evaluated. This gives rise to derivativelike spectral features in the photon energy region corresponding to inter-band transitions or critical points of the band structures.

To determine me* from this experimental approach, solid knowledge on some other parameters that are also important for interband transitions is required. For example, values of conduction- and valence-band offsets at the heterointerfaces, the hole effective mass, strain field, and exact QW width should be separately obtained or self-consistently fitted or assumed. Depending on the choices of these parameters, a large uncertainty can arise in some cases. 


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