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Ga 2 O 3 ( Gd 2 O 3 ) (GGO) directly deposited on Ge substrate in ultrahigh vacuum, without a passivation layer such as GeOxNy or Si, has demonstrated excellent electrical performances and thermodynamic stability. Energy-band parameters of GGO/Ge have been determined by in situ x-ray photoelectron spectroscopy in conjunction with reflection electron energy loss spectroscopy and current transport of Fowler–Nordheim tunneling. A conduction-band offset and a valence-band offset of ∼2.3 and ∼2.42 eV, respectively, have been obtained. Moreover, self-aligned Ge pMOSFETs of 1-μm-gate length using Al2O3/GGO as the gate dielectrics have shown a high drain current and a peak transconductance of 252 mA/mm, and 143 mS/mm, respectively.

Deep levels present in MOS capacitors, fabricated on GeSn epitaxial layers on Ge-on-Si substrates have been studied by Deep-Level Transient Spectroscopy (DLTS). The gate dielectric is composed of 9 nm Al2O3 deposited by Molecular Beam Epitaxy (MBE) on two different types of Interfacial Oxide Layers (IOL). It is shown that the density of interface traps (Dit) near the valence band edge is significantly reduced for GeSn epilayers compared with the same gate stack on a Ge cap. At the same time, several deep-level traps in the germanium depletion region have been observed, whereof the origin is discussed.

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