Abstract
The fractional quantized Hall state at the filling factor ν = 5/2 is of special interest due to its possible application for quantum computing. Here we report on the optimization of growth parameters that allowed us to produce two-dimensional electron gases (2DEGs) with a 5/2 gap energy up to 135 mK. We concentrated on optimizing the molecular beam epitaxy (MBE) growth to provide high 5/2 gap energies in ‘as-grown’ samples, without the need to enhance the 2DEGs properties by illumination or gating techniques. Our findings allow us to analyse the impact of doping in narrow quantum wells with respect to conventional DX-doping in AlxGa1−xAs. The impact of the setback distance between doping layer and 2DEG was investigated as well. Additionally, we found a considerable increase in gap energy by reducing the amount of background impurities. To this end growth techniques like temperature reductions for substrate and effusion cells and the reduction of the Al mole fraction in the 2DEG region were applied.
Highlights
Even 26 years after its discovery in 1987 [1] the first even denominator fractional quantized Hall state (FQHS) is still a hot topic in semiconductor physics
Molecular beam epitaxy (MBE) in the GaAs/AlGaAs material system represents the instrument of choice for creating such systems of ultra-high purity, which are often characterized via the 2DEGs electron mobility
Our findings clearly confirm that electron mobility alone is not the relevant quantity to judge the quality of a 2DEG structure with respect to FQHS features and especially the gap energy of the 5/2 state
Summary
Even 26 years after its discovery in 1987 [1] the first even denominator fractional quantized Hall state (FQHS) is still a hot topic in semiconductor physics For more than two decades, a number of high-mobility 2DEGs with 5/2 activation energies up to 560 mK have been analysed [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] Most of these results required prior illumination of the intrinsic 2DEG [7,8,9, 11,12,13,14, 18] or the use of gating techniques to enhance the quality of or create the 2DEG [16, 19]. We report on our findings to optimize sample quality and with that the size of the 5/2 activation gap by optimizing the MBE growth itself
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