Oxygen-Doped Si Epitaxial Film (OXSEF)

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Abstract
We propose a new wide-gap material, an oxygen-doped Si epitaxial film (OXSEF), for applications to Si heterobipolar transistors (HBTs). OXSEF containing several tens of at.% of oxygen can be grown on a Si substrate by depositing Si in about 10-6 Torr O2. OXSEF is literally almost a single crystal with an identical crystalline structure to Si, although it includes {111} twins as defects caused by oxygen. Temperature and O2 pressure dependences of oxygen concentration in OXSEF are dominated by oxygen adsorption on the Si surface. Oxygen atoms in OXSEF segregate to some extent toform incomplete oxides like SiO1.5, but complete phase separation as a mixture of Si and SiO2. regions does not occur, probably bcause of non-equilibrium conditions in MBE growth. Valence band discontinuity at the Si/OXSEF interface is deduced to be 0.26 eV based on photoelectrical measurements.