Spontaneous Polarization and Polarization-Induced Electron Sheet Charge of YbAlN on GaN: A First-Principles Study

The high spontaneous polarization in scandium-doped AlN (ScAlN) is being actively investigated for applications to various electronic devices. In this study, spontaneous polarization of ytterbium-doped AlN (YbxAl1-xN) was investigated by first-principles calculations. The magnitude of spontaneous polarization increases with increasing Yb concentration and reaches the maximum value of -0.3 C/m(2) at x = 0.5, which is comparable with that of ScAlN. Moreover, the results revealed the correlation between the lattice-constant ratio (c/a) of the wurtzite structure and spontaneous polarization. The value of spontaneous polarization is affected by the length of the Yb-N bonds along the c-axis in the wurtzite structure. The shorter Yb-N bonds compared with Al-N bonds and higher Born effective charge of Yb compared with Al are considered to be the main factors for the high spontaneous polarization of YbAlN. The polarization-induced electron sheet charge in YbAlN/GaN heterostructures is estimated to be comparable with that in ScAlN/GaN. These results suggest that YbAlN is a promising barrier layer for GaN-based high-electron-mobility transistors. At low Yb concentration, the lattice mismatch between YbxAl1-xN and the GaN buffer layer is very small. The polarization-induced interface sheet charge is affected by the sum of the spontaneous and piezoelectric polarization. In the case of YbAlN/GaN, the piezoelectric polarization is suppressed to a low level, and the effect of spontaneous polarization increases and leads to higher polarization-induced interface sheet charge.

Automated summary

This study investigated the spontaneous polarization of ytterbium-doped aluminum nitride and its correlation with the lattice-constant ratio of the wurtzite structure. The results suggest that YbAlN is a promising barrier layer for GaN-based high-electron-mobility transistors.