Polarization engineering of two-dimensional electron gas at ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructure

In this study, we present an investigation of the spontaneous and piezoelectric polarization in the ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructures using density functional theory calculations. The spontaneous polarization (Psp) was found to increase from 23.93 to 26.34 μC/cm2 when Al-content increase from 0% to 50%. With Al-content increasing, the strain-induced piezoelectric polarization (Ppe) increases, which negates the Psp, causing the total polarization (Ptot) of the epitaxy layer in the AlGaO/GaO heterostructure to remain almost constant across all Al compositions. Additionally, due to the ferroelectric nature of ε-Ga2O3, a high-density polarization-induced two-dimensional electron gas (2DEG) can be formed at the interface of polarization reversed ε-(AlxGa1–x)2O3/ε-Ga2O3 when an electric field is applied. Using the 1D Schrödinger–Poisson model, the 2DEG of polarization reversed ε-(Al0.125Ga0.875)2O3/ε-Ga2O3 was found to be 2.05 × 1014 cm−2, which is nearly ten times larger than that of GaN-based structures. Our work indicates that ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructure could play a key role attributed to the large polarization and capability in modulating the polarization for high-power electronic and radio frequency device applications.