Restricted-Access Al-Mediated Material Transport in Al Contacting of PureGaB Ge-on-Si p + n Diodes
- 363 Downloads
The effectiveness of using nanometer-thin boron (PureB) layers as interdiffusion barrier to aluminum (Al) is studied for a contacting scheme specifically developed for fabricating germanium-on-silicon (Ge-on-Si) p + n photodiodes with an oxide-covered light entrance window. Contacting is achieved at the perimeter of the Ge-island anode directly to an Al interconnect metallization. The Ge is grown in oxide windows to the Si wafer and covered by a B and gallium (Ga) layer stack (PureGaB) composed of about a nanometer of Ga for forming the p + Ge region and 10 nm of B as an interdiffusion barrier to the Al. To form contact windows, the side-wall oxide is etched away, exposing a small tip of the Ge perimeter to Al that from this point travels about 5 μm into the bulk Ge crystal. In this process, Ge and Si materials are displaced, forming Ge-filled V-grooves at the Si surface. The Al coalesces in grains. This process is studied here by high-resolution cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy that confirm the purities of the Ge and Al grains. Diodes are fabricated with different geometries and statistical current–voltage characterization reveals a spread that can be related to across-the-wafer variations in the contact processing. The I–V behavior is characterized by low dark current, low contact resistance, and breakdown voltages that are suitable for operation in avalanching modes. The restricted access to the Ge of the Al inducing the Ge and Si material transport does not destroy the very good electrical characteristics typical of PureGaB Ge-on-Si diodes.
KeywordsPure B pure Ga Ge-on-Si Ge diodes photodiodes Al-induced material mediation
The experimental work was performed in the former DIMES IC-processing line and measurement room, the staff of which the authors would like to thank for their support. This project is supported by a national funding from the Netherlands Agency IOP Photonics Devices project RASKIN and the Huygens Scholarship program as well as by an industrial funding from the ASM International.
This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- 2.E.D. Marshall, C.S. Wu, C.S. Pai, D.M. Scott, and S.S. Lau, in MRS Spring Meeting, ed. by C.R. Aita, and K.S. SreeHarsha. Symposium C, vol 47 (San Fransisco, 15–18 April, 1985).Google Scholar
- 7.A. Sammak, M. Aminian, L. Qi, W.B. de Boer, E.Charbon, and L.K. Nanver, International Electron Devices Meeting, p.␣8.5.1 (2011).Google Scholar
- 11.A. Sammak, L. Qi, W.B. de Boer, and L.K. Nanver, 2010␣10th IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT), p. 969 (2010).Google Scholar
- 18.A. Sammak, M. Aminian, L.K. Nanver, and E. Charbon, IEEE Transactions on Electron Devices, Special Issue on Solid-State Image Sensors (2015).Google Scholar
- 25.V. Mohammadi, S. Ramesh, and L.K. Nanver, IEEE Conference on Microelectronic Test Structures (ICMTS), vol. 1 (Udine, Italy, March 24–27, 2014).Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.