Fermi-Level Unpinning Technique with Excellent Thermal Stability for n-Type Germanium

Gwang Sik Kim, Seung Hwan Kim, Tae In Lee, Byung Jin Cho, Changhwan Choi, Changhwan Shin, Joon Hyung Shim, Jiyoung Kim, Hyun Yong Yu

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


A metal-interlayer-semiconductor (M-I-S) structure with excellent thermal stability and electrical performance for a nonalloyed contact scheme is developed, and considerations for designing thermally stable M-I-S structure are demonstrated on the basis of n-type germanium (Ge). A thermal annealing process makes M-I-S structures lose their Fermi-level unpinning and electron Schottky barrier height reduction effect in two mechanisms: (1) oxygen (O) diffusion from the interlayer to the contact metal due to high reactivity of a pure metal contact with O and (2) interdiffusion between the contact metal and semiconductor through grain boundaries of the interlayer. A pure metal contact such as titanium (Ti) provides very poor thermal stability due to its high reactivity with O. A structure with a tantalum nitride (TaN) metal contact and a titanium dioxide (TiO2) interlayer exhibits moderate thermal stability up to 400 anddeg;C because TaN has much lower reactivity with O than with Ti. However, the TiO2 interlayer cannot prevent the interdiffusion process because it is easily crystallized during thermal annealing and its grain boundaries act as diffusion path. A zinc oxide (ZnO) interlayer doped with group-III elements, such as an aluminum-doped ZnO (AZO) interlayer, acts as a good diffusion barrier due to its high crystallization temperature. A TaN/AZO/n-Ge structure provides excellent thermal stability above 500 anddeg;C as it can prevent both O diffusion and interdiffusion processes; hence, it exhibits Ohmic contact properties for all thermal annealing temperatures. This work shows that, to fabricate a thermally stable and low resistive M-I-S contact structure, the metal contact should have low reactivity with O and a low work-function, and the interlayer should have a high crystallization temperature and a low conduction band offset to Ge. Furthermore, new insights are provided for designing thermally stable M-I-S contact schemes for any semiconductor material that suffers from the Fermi-level pinning problem. andcopy; 2017 American Chemical Society.

Original languageEnglish
Pages (from-to)35988-35997
Number of pages10
JournalACS Applied Materials and Interfaces
Issue number41
Publication statusPublished - 2017 Oct 18

Bibliographical note

Funding Information:
This work was supported in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2017R1A2B4006460), in part by the Technology Innovation Program (10048594, Technology Development of Ge nMOS/pMOS FinFET for 10 nm Technology Node) funded by the Ministry of Trade, Industry & Energy (MI Korea), and in part by the Nano·Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (2016M3A7B4910426).


  • Schottky barrier height
  • aluminum-doped zinc oxide
  • germanium
  • metal-interlayer-semiconductor structure
  • tantalum nitride
  • thermal stability

ASJC Scopus subject areas

  • General Materials Science


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