The role of coherent epitaxy in forming a two-dimensional electron gas at LaIn1-xGaxO3/BaSnO3 interfaces

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.