Success in Spectroscopy of Impurities in Germanium Nanowires with Diameter of 20nm

Establishment of New Characterization Technology for Next-generation Vertical Transistor Materials

2010.07.15

National Institute for Materials Science
Japan Science and Technology Agency

The National Institute for Materials Science succeeded in nondestructive/noncontact detection of the states of dopant impurities introduced for carrier control in germanium nanowires (diameter: 20nm or less), which have attracted attention as a next-generation semiconductor material with the potential to replace silicon.

Abstract

  1. The National Institute for Materials Science (NIMS; President: Sukekatsu Ushioda) succeeded in nondestructive/noncontact detection of the states of dopant impurities introduced for carrier control in germanium nanowires (diameter: 20nm or less), which have attracted attention as a next-generation semiconductor material with the potential to replace silicon. This result was obtained by a research group headed by Dr. Naoki Fukata, who is a MANA Independent Scientist at the NIMS International Center for Materials Nanoarchitectonics (MANA; Director General: Masakazu Aono).
  2. The current mainstream in semiconductor transistor materials is silicon. Miniaturization of the size of these transistors with the aim of improving performance, for example, to achieve higher speed operation, has progressed year by year. However, due to the problems of increased leakage current, heat generation, etc., additional improvement in performance cannot be expected without innovations in materials and structures, even assuming further miniaturization along the same lines. Because the mobility of electrons in germanium is two times greater than that in silicon, and the mobility of holes is 4 times greater, realization of high speed devices which surpass the performance of the current silicon transistors can be expected. Furthermore, vertical transistors, which do not have the conventional planar configuration, can be realized by using germanium in a 1-dimensional nanowire structure. This will make it possible to achieve various functional and structural innovations simultaneously. For example, reduction of leakage current, reduction of heat generation by low power consumption, and dramatically higher integration than in the existing LSIs can be expected.
  3. The key issues for germanium-based transistors include how to perform doping for carrier control in fine nanowire semiconductors and how to observe the states of the doped impurities. In the present research, the NIMS group established a method in which boron (p-type) and phosphorus (n-type) are introduced as dopants during the growth of germanium nanowires. Highly uniform impurity-doped germanium nanowires were successfully fabricated, and the chemical bonding states and electrical activity of the doped impurities were successfully observed simultaneously by a noncontact, nondestructive technique for the first time. This was made possible by observation of the local vibrational peaks and Fano resonance of the impurities with a micro-Raman spectroscopy equipped with a high sensitivity detector and the establishment of a new analytical technique.
  4. This research was carried out as part of the research topic “Development of Semiconductor Nanowires for the Realization of Vertical Three-Dimensional Semiconductor Devices” (Researcher: Naoki Fukata) in the research area of “Materials and Processes for Innovative Next-Generation Devices” (Research Supervisor: Katsuaki Sato) of the independent research by individuals (PRESTO; Precursory Research for Embryonic Science and Technology) in the Japan Science and Technology Agency (JST) Basic Research Program. The results were published online on June 21 in ACS NANO (publication of the American Chemical Society; paper: Naoki Fukata et al., “Doping and Raman characterization of boron and phosphorus atoms in germanium nanowires”, ACS NANO, Volume4, Issue7, 3807-3816, 2010).