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Open Access Publications from the University of California

Molecular beam epitaxy of wide-band gap perovskiteoxides: (Ba, Sr)TiO3 and BaSnO3

  • Author(s): Freeze, Christopher R
  • Advisor(s): Stemmer, Susanne
  • et al.

Perovskite oxides have long been lauded for their array of technologically useful properties, along with the promise of monolithic integration due to their compatible structure. Despite this potential, few real-world applications have yet to make it to market. This work aims to demonstrate the capabilities of the perovskite family of materials through two main applications – a tunable dielectric in the radio frequency regime and a high-power-density channel material for power switching. These capabilities are largely enabled thanks to the high-quality films grown by molecular beam epitaxy (MBE).

BaxSr1-xTiO3 (BST) is a ferroelectric material with a Curie temperature tuned by the composition x. It has been extensively investigated as a tunable dielectric material for devices such as phase shifters, tunable antennas, and matching networks. Despite decades of work, BST grown by other methods cannot compete with the extremely high performance of MBE-grown material. This thesis considers which aspects of the MBE-grown material are most critical for this performance increase.

While extreme charge density beyond 1020 cm-3 and charge modulation above 1014 cm-2 have been achieved in oxide systems, the low mobilities of most oxides at room temperature has limited their utility in power-switching applications. A relatively new system, BaSnO3, shows great promise for this purpose, with bulk mobility above 300 cm2/V·s at carrier densities of 8×1019 cm-3. This work discusses continued efforts to understand the growth of BaSnO3 by MBE. The goal is to leverage this understanding to enhance thin-film mobility and control doping to enable high-power transistors, which may even outperform state-of-the-art GaN technologies. To that end, heterostructures with perovskite titanate top gates are investigated for modulation doping and gating.

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