Wannier-Stark localization in semiconductor superlattices

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In this project we have investigated Wannier-Stark localization phenomena in semiconductor superlattices, aiming at clucidating the fundamental spectroscopic and tunneling transporl properties of the ultra-thin quantum heterostructures under high electric fields. In the artificially designed and fabricated superlattices as coupled-quantum-wells systems, varlous interesting quantum phenomena have emerged as a result of Stark effects on the quantized miniband states. By employing mainly optical methods such as photocurrent, photoluminescence, photoluminescence excitation and electroreflectance, key factors have been clarified which affect the spectroscopic structures and the tunneling transport properties of photogenerated carriers involving with optical absorption, recombination and tunneling processes. The following results are obtained from studies of this project : (1) fundamental band-edge absorption propeties of GaAs/AlAs superlattices with different miniband widths and their ralationship with the miniband dispersion, (2) correlation between the heterointerface fluctuations and the spectral and lateral photoluminescence properties, (3) dynamic transmission intensity oscillations due to the Starkladder resonances, (4) correlation between the radiative recombinations and tunneling and lateral transport properties of photogenaraied carriers, (5) quantum interference between the Stark ladder localized states associated with different subbands, (6) oscillator strengths of the excitonic Stark ladder transitions and their dependence on the miniband width, (7) optical properties of quasi-bound Stark ladder localized srates.