Achieving surface recombination velocity below 10 cm/s in n-type Germanium using ALD Al2O3

Joonas Isometsä*, John Fung, Toni Pasanen, Hanchen Liu, Marko Yli-Koski, Ville Vähänissi, Hele Savin

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)
97 Downloads (Pure)


Desirable intrinsic properties, namely, narrow bandgap and high carrier mobility, make germanium (Ge) an excellent candidate for various applications, such as radiation detectors, multi-junction solar cells, and field effect transistors. Nevertheless, efficient surface passivation of Ge has been an everlasting challenge. In this work, we tackle this problem by applying thermal atomic layer deposited (ALD) aluminum oxide (Al2O3), with special focus on the process steps carried out prior to and after dielectric film deposition. Our results show that instead of conventional hydrofluoric acid (HF) dip, hydrochloric acid (HCI) pre-treatment is an essential process step needed to reach surface recombination velocities (SRVs) below 10 cm/s. The main reason for efficient surface passivation is found to be a high dielectric charge that promotes the so-called field-effect passivation. Furthermore, the results demonstrate that the post-deposition anneal temperature, time, and ambient play a role in passivating Ge-dangling bonds, but surprisingly, good surface passivation (SRV below 26 cm/s) is obtained even without any post-deposition annealing. The results pave the way for high-performance n-type Ge optoelectronic devices that could use induced junctions via negatively charged Al2O3 layers.

Original languageEnglish
Article number111113
Number of pages7
JournalAPL Materials
Issue number11
Publication statusPublished - 1 Nov 2021
MoE publication typeA1 Journal article-refereed


  • Ge
  • inversion
  • minority carrier lifetime
  • chemical pre-treatment
  • field-effect
  • surface passivation


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