Local inhomogeneities resolved by scanning probe techniques and their impact on local 2DEG formation in oxide heterostructures

Abstract

Lateral inhomogeneities in the formation of 2-dimensional electron gases (2DEG) directly influence their electronic properties. Understanding their origin is an important factor for fundamental interpretations, as well as high quality devices. Here, we studied the local formation of the buried 2DEG at LaAlO3/SrTiO3 (LAO/STO) interfaces grown on STO (100) single crystals with partial TiO2 termination, utilizing in-situ local conductivity atomic force microscopy (LC-AFM) and scattering-type scanning near-field optical microscopy (s-SNOM). Using substrates with different degrees of chemical surface termination, we can link the resulting interface chemistry to an inhomogeneous 2DEG formation. In conductivity maps recorded by LC-AFM, a significant lack of conductivity is observed at topographic features, indicative of a local SrO/AlO2 interface stacking order, while significant local conductivity can be probed in regions showing TiO2/LaO interface stacking order. These results could be corroborated by s SNOM, showing a similar contrast distribution in the optical signal which can be linked to the local electronic properties of the material. The results are further complimented by low-temperature conductivity measurements, which show an increasing residual resistance at 5 K with increasing portion of insulating SrO terminated areas. Therefore, we can correlate the macroscopic electrical behavior of our samples to its nanoscopic structure. Using proper parameters, 2DEG mapping can be carried out without any visible alteration of sample properties, proving LC AFM and s SNOM to be viable and destruction-free techniques for the identification of local 2DEG formation. Furthermore, applying LC AFM and s SNOM in this manner opens the exciting prospect to link macroscopic low temperature transport to its nanoscopic origin.

References in corpus (13)

• Why Some Interfaces Cannot be Sharp
• The role of oxygen vacancies in SrTiO3 at the LaAlO3/SrTiO3 interface
• Mapping the Spatial Distribution of Charge Carriers in LaAlO3/SrTiO3 Heterostructures
• Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures
• Locally enhanced conductivity due to the tetragonal domain structure in LaAlO${}_3$/SrTiO${}_3$ heterointerfaces
• Built-in and induced polarization across LaAlO${}_3$/SrTiO${}_3$ heterojunctions
• Control of electronic conduction at an oxide heterointerface using surface polar adsorbates
• Local Electrostatic Imaging of Striped Domain Order in LaAlO3/SrTiO3
• Parallel electron-hole bilayer conductivity from electronic interface reconstruction
• Charge writing at the LaAlO3/SrTiO3 surface
• Pascal conductance series in ballistic one-dimensional LaAlO${}_3$/SrTiO${}_3$ channels
• Growth-induced electron mobility enhancement at the LaAlO${}_3$/SrTiO${}_3$ interface
• Instability and Surface Potential Modulation of Self-Patterned (001)SrTiO3 Surfaces