Local optical phenomena in InAs/GaAs heterostructures with doped quantum dots and artificial molecules (Seoul, Korea)

abstract

English

In a bulk 3-D semiconductor material, the interaction between atoms in the crystal lattice extends the energy levels of free electron and hole charge carriers into a continuous spectrum. Transition due to the stimulated recombination of electron-hole pairs between conduction and valence bands results in light emission over a broad distribution of wavelengths. The deposition of thin layers makes possible the freedom of motion of charge carriers to be localized by confinement on a nanometer-scale in one, two or three dimensions between heteroboundaries with wider bandgap surrounding materials. This restricts carriers to 2-D quantum wells, 1-D quantum wires or 0-D quantum dots. Such size quantization in the confined directions concentrates available energy levels for injected carriers into the increased density of states near the band edges. In the case of the QDs, localized carriers confined in all three dimensions have their density of states concentrated into fully quantizated, discrete and hence mode widely separated energy levels. Optical transitions between them are therefore restricted to emission at fewer wavelengths with atomic-like spectrally narrowed linewidths. These wavelengths are not determined solely by the fixed bandgap energy of the active region material, but also by the QDs energy levels, which depend on QD size and band offsets at the heteroboundary. This property allow tune over a wider range. Therefore an investigation of internal optical transitions of charge carriers in the quantum dots (QDs) is of a vital importance for the design of new optoelectronic devices as sources and detectors operating in near and mid infrared domains. The photoinduced internal absorption in undoped InAs/GaAs quantum dots and an absorption in undoped n-type QDs has been studied, but the data proceeded from internal intrazonal light absorption in the n-type QDs as well as an analysis of absorption in n- and p-types are still missing. Among different other characteristics, these data might be interesting especially for the evaluation of optical losses, due to the light absorption by holes in the laser with internal transition of electrons in the QDs. This paper brings an experimental and theoretical study of internal absorption in InAs/GaAs quantum dots. The comparison of the near- and far-field induced photoabsorption will be also provided.

InAs/GaAs heterostructure, quantum dots, artificial molecules, near-field, local optical phenomena,

TOMÁNEK, P., GRMELA, L.

5. 9. 2004

Seoul National University

Seoul, Korea

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