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

Title
Fermi-Level Unpinning Technique with Excellent Thermal Stability. for n-Type Germanium
Author
최창환
Keywords
germanium; metal-interlayer-semiconductor structure; thermal stability; Schottky barrier height; tantalum nitride; aluminum-doped zinc oxide
Issue Date
2017-09
Publisher
AMER CHEMICAL SOC
Citation
ACS APPLIED MATERIALS & INTERFACES, v. 9, no. 41, page. 35988-35997
Abstract
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 degrees 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 degrees 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.
URI
https://pubs.acs.org/doi/10.1021/acsami.7b10346https://repository.hanyang.ac.kr/handle/20.500.11754/115462
ISSN
1944-8244
DOI
10.1021/acsami.7b10346
Appears in Collections:
COLLEGE OF ENGINEERING[S](공과대학) > MATERIALS SCIENCE AND ENGINEERING(신소재공학부) > Articles
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