Abstract
We report on controllable tuning of intersubband transitions in ZnO/Zn0.60Mg0.40O multiple quantum well structures grown by molecular beam epitaxy on sapphire. The transitions from the first to the second electronic energy state within the conduction band are directly observed by infrared spectroscopy. By variation of the quantum well width, the intersubband transition energies are tuned from 290 to 370 meV. The experimental results are in good agreement with theoretical calculations assuming the presence of internal electric fields of 2 MV·cm−1.
Highlights
Due to its wide band gap of 3.4 eV and high exciton binding energy (∼ 60 meV), ZnO has been considered as a promising candidate for laser and light emitting diodes in the visible and ultraviolet spectral region
This is despite the fact that n-doping of ZnO can be achieved enabling fabrication of plasmonic waveguides and the technique to fabricate high-quality ZnO/ZnMgO multiple quantum well (MQW) structures is well established.[10,11,12]
Only intersubband transitions (ISBT) from the first to the second electronic energy state in ZnO/ZnMgO MQWs have been directly observed at about 400 meV,[13] and a weak photocurrent at low temperature due to the transition from the first to the third electronic energy state was reported.[14]
Summary
Due to its wide band gap of 3.4 eV and high exciton binding energy (∼ 60 meV), ZnO has been considered as a promising candidate for laser and light emitting diodes in the visible and ultraviolet spectral region. Tunable intersubband transitions in ZnO/ZnMgO multiple quantum wells in the mid infrared spectral range Interband transitions in ZnO-based quantum wells (QWs) can be tuned within a wide spectral range.
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