Ab Initio Design of High-$k$ Dielectrics: ${\mathrm{La}}_x{\mathrm{Y}}_{1-x}{\mathrm{AlO}}_3$

We use calculations based on density-functional theory in the virtual crystal approximation for the design of high-$k$ dielectrics, which could offer an alternative to silicon dioxide in complementary metal-oxide semiconductor devices. We show that aluminates ${\mathrm{La}}_x{\mathrm{Y}}_{1-x}{\mathrm{AlO}}_3$ alloys derived by mixing aluminum oxide with lanthanum and yttrium oxides have unique physical attributes for a possible application as gate dielectrics when stabilized in the rhombohedral perovskite structure, and which are lost in the orthorhombic modification. Stability arguments locate this interesting composition range as $0.2<x<0.4$. Phase separation in microdomains is shown to have the tendency to further enhance the dielectric constant. We propose this as a novel family of high-$k$ dielectrics deserving experimental exploration.

Figure 1

Calculated infrared spectrum for ${\mathrm{LaAlO}}_3$ and ${\mathrm{YAlO}}_3$ in the LAP structure. On the right-hand side, the atomic displacements in the unit cell are depicted, which correspond to the $A(A_{2u})$ and $B(E_u)$ phonons.

Figure 2

${\mathrm{La}}_x{\mathrm{Y}}_{1-x}{\mathrm{AlO}}_3$: Calculated dielectric constants, both static and high-frequency values, vs lanthanum concentration. (a) Average values; (b) maximum components.