MBE-grown Ge 1-x C x nanocrystals by using a novel bio-nanoprocess due to protein "ferritin" Yuji Nakama 1 , Jun Ohta 1 and Masahiro Nunoshita 1 1 Graduate School of Materials Science, Nara Institute of Science and Technology 8916-5 Takayama, Ikoma, Nara 630-0101, Japan Phone: +81-743-72-6054, Fax: +81-743-72-6052, e-mail: n-yuuji@ms.naist.jp 1. Introduction The research for Si-based optoelectronic devices has been an important subject, especially for such an applica- tion to Si-based optoelectronic IC (OEIC) or Si photonics. As for the Si-based optoelectronic materials, Si nanocrys- tals, β-FeSi 2 , SiGe superlattices and Ge 1-x C x epilayers are known. We have studied on Ge 1-x C x epilayers, which with a C content of 4%<x<11% are considered likely to have a direct-transition-type band structure [1] and little lattice mismatch with a Si substrate [2]. Until now, Ge 1-x C x of x=3% was realized using an arc-plasma gun as a new C source. However, the remarkable bandboring occurs [3]. In this work, a development of high-density and very small diameter (<φ10 nm) Ge 1-x C x nanocrystals on a Si(100) substrate is carried out by using a novel bio-nanoprocess and a solid source MBE technique. As a final object, Ge 1-x C x nanocrystals with a direct-transition-type band and/or a quantum confinement effect are aiming to realize new strongly light-emitting devices. 2. Experiments Fig. 1 shows a schematic of bio-nanoprocess with self-arranged ferritins and subsequent MBE growth process of Ge 1-x C x nanocrystals using a Si thin film nanomask. Fig.1 Schematic of process flow of fabricating Ge 1-x C x nanocrystals using bio-nanoprocess and MBE growth tech- nique An n-type Si(100) wafer with a thermally grown SiO 2 layer (thickness 10 nm) was used as the substrate. The sub- strate was cleaned using an UV dry cleaner (Fig. 1(1)). 2-D arrangement of ferritins was fabricated on the surface of substrate by the so-called bio-nanoprocess. The ferritins have a diameter of 12 nm, and their inside iron-oxide (Fe 2 O 3 ) core of a diameter of 7 nm. The detail of bio-nanoprocess was reported elsewhere [4]. Then, the pro- teins were removed at 300℃, for 10 min in the IR furnace (O 2 flow-rate 1 l/min and programming rate 5℃/ min). The sample was conveyed by molecular beam epitaxial growth chamber (2-chamber MBE:Eiko EV-100), and then a 2 nm-thick Si ultra-thin film was deposited on the sub- strate at 28℃ in a vacuum (1x10 -9 Torr) by using an elec- tron-beam evaporating cell(Fig. 1(2)). The sample was taken out of the chamber, and the Fe 2 O 3 cores were re- moved by dipping in hydrochloric acid at room temperature for 30 minutes (Fig. 1(3)). As the result of this process, the Si nanomask with the ultra-fine holes 7 nm in diameter was fabricated. Through this nanomask, the 10 nm-thick SiO 2 layer on the Si substrate was etched away for 2 sec by reac- tive ion etching (RIE) using etching gas CF 4 (20 sccm) + H 2 (10 sccm) at a pressure of 1 Pa under the conditions of ICP electric power 125W, bias power 10W (Fig. 1(4)). The sample was again conveyed into the same MBE growth chamber, where the natural SiO 2 film was removed at 900℃ for 30 min in a vacuum (1x10 -9 Torr). All Ge 1-x C x compound layers were grown at a substrate temperature T s of 500℃ in a vacuum (5x10 -9 Torr) by supplying Ge flux from a K-cell and pulsed C molecular beam from a vac- uum-type arc-plasma gun (ULVAC APG-1000) as de- scribed in detail elsewhere [3]. The substitutional C com- position x of Ge 1-x C x epilayer was controlled by the sup- plied amount of C. Without the nanomask, Ge 1-x C x nanocrystals due to the S-K mode were formed at random to have diameters of 10 to 20 nm. With the nanomask, a 1nm thick C film was first deposited at Ts=500℃ and 5x10 -9 Torr, and subsequently a 3 nm thick Ge 1-x C x epilayer with x=1.5% was grown under the same conditions. The sample taken out of the chamber was dipped in hydroflu- oric acid at room temperature for 30 min to remove the SiO 2 layer and to lift-off the Si nanomask and Ge 1-x C x film. As a result, the Ge 1-x C x nanocrystals of high density and uniform size were fabricated (Fig. 1(5)). Photoluminescence (PL) spectra were measured by Ar + laser (wavelength 488 nm and laser power 2.5 kW/cm 2 ). The samples were cooled down in a cryostat and their PL spectra were detected by a liquid-nitrogen cooled Ge pho- Sub unit Fe 2 O 3 core Protein diameter:12 nmφ Fe 2 O 3 core diameter:7 nmφ 2D-arrangement by self-organization 2D-arrangement by bio-nano process of feritiin ferittin SiO 2 layer Si substrate (1)2D-arrangement of ferittin Reactive ion etching (RIE) of SiO 2 layer ultra-fine hole (Removal of Fe 2 O 3 core) Removal of Fe 2 O 3 core by lift-off method (formation of ultrafine hole） (3) Formation of nanomask Protein “feritiin” Fe 2 O 3 core Si thin film SiO 2 layer Si substrate Removal of protein by UV/O 3 Vapor deposition of Si thin film (2) Removal of protein and vapor deposition of Si thin film Si substrate MBE growth of GeC nanocrystals Removal of SiO 2 and Si (5)MBE growth and GeC nanocrystal removal of nanomask (4)Etching of SiO 2 layer Extended Abstracts of the 2007 International Conference on Solid State Devices and Materials, Tsukuba, 2007, -782- F-6-1 pp. 782-783