Abstract
Some oxide interfaces are known to exhibit unique properties such as a 2D electron gas, controlled by epitaxial strain and coherency between the two layers. Here, we study variation in the 2D electron density in the polar LaIn1-xGaxO3/Ba0.997La0.003SnO3 interface with changing x and LaIn1-xGaxO3 layer thickness. We find that the 2D electron density decreases as the gallium alloying ratio increases and the interface conductance eventually disappears, which shows that an interface with polar discontinuity is not a sufficient condition for 2D electron gas formation. The interface conductance reaches its maximum value when the LaIn1-xGaxO3 layer thickness is approximately 20 Å, beyond which conductance decreased to a constant value. Atomistic imaging reveals that dislocations start to form as the gallium ratio increases, forming away from the interface and then moving closer with increasing gallium alloying. The dislocations eventually destroy coherency in the case of LaGaO3 and suppress the formation of a 2D electron gas.
Highlights
Some oxide interfaces are known to exhibit unique properties such as a 2D electron gas, controlled by epitaxial strain and coherency between the two layers
While the polar catastrophe model can account for the observation of the critical thickness for conduction, there are some experimental findings that are hard to explain using the polar catastrophe model: the 2DEG density much lower than 3 × 1014 cm−2 which is expected from the model and no observation yet of the isolated conducting p-type interfaces on an AlO2-terminated LaAlO3 surface in spite of some related experimental and theoretical studies[17,18]
We found that in-plane lattice constant of LaIn1−x GaxO3 (LIGO) near the interface was almost pinned with that of BLSO up to 61% Ga ratio and began to relax from 81% Ga ratio
Summary
Some oxide interfaces are known to exhibit unique properties such as a 2D electron gas, controlled by epitaxial strain and coherency between the two layers. It was proposed that the 2DEG formation may be related with the polar nature of LIO, since the interfaces of nonpolar BaHfO3 or SrZrO3 with La-doped BSO (BLSO) showed no conductance enhancement[20], while the effect of oxygen vacancies and cation diffusion on the conductance of the interface have been tested and ruled out It has been suggested[22] that polarization in LIO near the interface with BSO induces 2DEG, based on the experimental data that showed the n2D increases for the first 16 Å (~4 unit cells) of LIO, starts to decrease for thicker LIO, and approaches to a constant value for thicker LIO beyond 100 Å (~25 unit cells). We have chosen LaGaO3 (LGO), which is a polar perovskite oxide like the LIO and share the same orthorhombic structure of lattice constant of the GdFeO3tpypffieffiffi2ffiffi5ffiffi–ffiffi2ffiffi7ffi.ffiffi LIO, apc1⁄4 a2 þ b2
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