Optimal Oxide Passivation of Ge for Optoelectronics

Oxide passivation is an active field of investigation for reducing surface state densities on Ge surfaces, namely below high-K gate stacks. However, the quality of Ge oxide passivation has not been as widely investigated in the context of performance in minority carrier photonic devices. p-Ge substrates with a foundry-applied oxide passivation are compared with oxide-stripped substrates passivated by dry thermal oxides grown between 400 ◦ C-650 ◦ Ci n O2. By using p-Ge, only the behavior of minority conduction electrons and their associated traps become the relevant focus of this study. Passivation quality, as evaluated by photoluminescence (PL),isfoundtovaryasafunctionoftemperaturebetween400‐650 ◦ C.ChangesinPLintensityareattributedtodifferencesinsurface terminationofthep-Gesubstrate.X-rayphotoelectronspectroscopy(XPS)studiesfindthatthepresenceofsuboxides(GeOx)increase with oxidation temperature, with GeO2 dominant at 400 ◦ C and mixed suboxides at higher temperatures. Nonuniform desorption of Ge oxide is confirmed above 550 ◦ C. Thermal oxidation is also shown to improve the quality of ion-damaged Ge surfaces. We conclude that suboxides confer better passivation than a GeO2 interface, as determined by PL intensity.