The objectives of this thesis work are to theoretically identify type-II GaAs/ AlAs superlattices with pseudo-direct band gaps (i.e. direct in wave vector space but indirect in real space) which exhibit high photoluminescence intensities, and to experimentally demonstrate that....[ Read more ]

The objectives of this thesis work are to theoretically identify type-II GaAs/ AlAs superlattices with pseudo-direct band gaps (i.e. direct in wave vector space but indirect in real space) which exhibit high photoluminescence intensities, and to experimentally demonstrate that.

The empirical tight-binding model is utilized to calculate properties of super-lattices, such as band edges, oscillator strengths and effective masses.

Prior to calculations we identify two parameterizations with respect to their usability in superlattice calculations on grounds of minimizing the unknown cross interface parameters and then thoroughly analyse them in calculations of opto-electronic properties of constituent bulk compounds and superlattices. Bench-marked with experimental data, we choose one parameterization for our further studies.

We conduct calculations on a wide range of GaAs/AlAs superlattices and select three type-II structures with exceptionally high oscillator strengths, which is the dominant factor for strong photoluminescence.

These structures were fabricated using Molecular Beam Epitaxy (MBE) and their photoluminescence properties were investigated at temperatures between 12 K and 200 K and at different excitation intensities.

Our experimental work achieved two findings. Firstly, all structures exhibit the predicted strong low temperature photoluminescence arising from pseudo-direct recombinations. Secondly, one superlattice shows stimulated emission from a direct recombination, which has not been observed in type-II systems before.