High On/Off ratio and very low leakage in p⁺/n and n ⁺/p germanium/silicon heterojunction diodes

We demonstrate the characteristics of p⁺-Ge/n-Si and n ⁺-Ge/p-Si heterojunction diodes with a very high on/off ratio and very low leakage current using heteroepitaxial Ge grown directly on Si. The current ratio of p⁺-Ge/n-Si and n⁺-Ge/p-Si heterojunction is ∼5 × 10⁷ and ∼3 × 10⁶, respectively. The remarkably low off current density is 2.1 μA/cm² for p⁺-Ge/n-Si and 19 μA/cm² for n⁺-Ge/p-Si at a reverse bias of |V_F| = ±1 V, respectively. High on current density (125 A/cm² for p⁺-Ge/n-Si and 54 A/cm ² for n⁺-Ge/p-Si) with a forward bias |V_F| = ±1 V is obtained with a GeO₂ passivation and an Al ₂O₃ isolation.