Comparison of SiNx‐Based Surface Passivation Between Germanium and Silicon. Issue 2 (20th December 2022)

• Record Type: Journal Article
• Authors: Liu, Hanchen; Pasanen, Toni P.; Fung, Tsun Hang; Isometsä, Joonas; Leiviskä, Oskari; Vähänissi, Ville; Savin, Hele
• Is Part Of: Physica status solidi. Volume 220:Issue 2(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-20
• Subjects: aluminum oxide -- charge -- germanium -- interface defect density -- silicon nitride -- surface passivation; Solid state physics -- Periodicals; Solids -- Industrial applications -- Periodicals; 530.41
• DOI: 10.1002/pssa.202200690
• Languages: English
• ISSNs: 1862-6300

Abstract

Abstract : Germanium (Ge) has attracted much attention as a promising channel material in nanoscale metal–oxide–semiconductor devices and near‐infrared sensing because of its high carrier mobilities and narrow bandgap, respectively. However, efficient passivation of Ge surfaces has remained challenging. Herein, silicon nitride (SiN x )‐based passivation schemes on Ge surfaces are studied and the observations are compared to Si counterparts. These results show that instead of a high positive charge density ( Q tot ) that is found in SiN x ‐passivated Si samples, similar Ge samples contain a high amount of negative Q tot (in the range of 10 12 cm −2 ). The maximum surface recombination velocity of the samples is shown to reduce by a factor of three in both Si and Ge samples by a post‐deposition anneal at 400 °C. The SiN x ‐coated samples are capped with an atomic‐layer‐deposited aluminum oxide (Al2 O3 ) layer, which reduces the midgap interface defect density ( D it ) after annealing to 7 × 10 10 and 4 × 10 11 cm −2 eV −1 in Si and Ge, respectively. Interestingly, while the Al2 O3 capping seems to have no impact on Q tot of the Si samples, it turns the stack virtually neutral (∼−1.6 × 10 11 cm −2 ) on Ge. The presented SiN x ‐based passivation schemes are promising for optoelectronic devices, where a low D it and/or a low charge are favored. Abstract : Unexpected negative charge density is found in SiN x on Ge, opposite to high positive charge in Si/SiN x . Surface passivation is enhanced by depositing an atomic‐layer‐deposited (ALD) Al2 O3 capping on SiN x followed by annealing. The capping layer has no impact on the charge of the Si samples while it turns the stack virtually neutral on Ge.