| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF1-ThM |
| Session: | Control and Modeling of Thin Film Growth and Film Characterization |
| Presenter: | Bharat Jalan, University of Minnesota |
| Authors: | A. Prakash, University of Minnesota P. Xu, University of Minnesota J. Dewey, University of Minnesota B. Jalan, University of Minnesota |
| Correspondent: | Click to Email |
We will present on the growth of phase-pure, epitaxial BaSnO3 films using a novel radical-based molecular beam epitaxy (MBE) approach with scalable growth rates [1]. In this approach, we use a metal-organic precursor (hexamethylditin) as a tin source, a solid effusion cell for barium, and an rf plasma source for oxygn. BaSnO3 films were grown on SrTiO3 (001), LaAlO3 (001) and LSAT (001) substrates. The substrate temperature and oxygen pressure were kept fixed at 900° C, and 5x10-6 Torr respectively whereas Ba/Sn beam equivalent pressure (BEP) ratio was varied to optimize cation stoichiometry. The unstrained lattice parameter determined using high-resolution X-ray diffraction, and the Rutherford backscattering spectroscopy (RBS) were used to optimize cation stoichiometry. Lanthanum was used as n-type dopants.
Stoichiometric composition yielded an unstrained lattice parameter value of 4.116±0.001Å, which is identical to that of bulk BaSnO3. This value was found to increase for Ba-rich films whereas Sn-rich films resulted into secondary phase formation. A range of Ba/Sn flux ratio was identified where films cation stoichiometry was self-regulating indicating the presence of a "MBE growth window". Time-dependent reflection high-energy electron diffraction (RHEED) intensity oscillations were observed during film growth indicating films grew in a layer-by-layer fashion. Atomic force microscopy confirmed smooth surface morphology for stoichiometric films. Non-stoichiometry films showed surface nanocrystallites, which correlated with the film stoichiometry. Most remarkably, phase-pure BaSnO3 could also be grown with the molecular oxygen (i.e. without any rf plasma) suggesting an important role of reactive radical chemistry during film growth. We will discuss these results in the context of highly reactive Sn radicals growth mechanism that assist with the reaction and compound formation.
Finally, we will present a comprehensive electrical characterization of La-doped BaSnO3 and will discuss how electrical transport is influenced by the presence of structural defects such as dislocations, non-stoichiometry, and dopant concentration. We will also present different scattering mechanisms in La-doped BaSnO3 that limits the room temperature electron mobility. We will present pathways to suppress these scattering rates - a step closer towards defect-managed high mobility oxide thin films and heterostructure.
Work supported by the NSF, and the AFOSR YIP Program.
[1] A. Prakash, J. Dewey, H. Yun, J.S. Jeong, K.A. Mkhoyan, and B. Jalan, “Hybrid molecular beam epitaxy for growth of stoichiometric BaSnO3”, J. Vac. Sci. Technol. A, 33, 060608 (2015).