In:
ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 30 ( 2016-09-01), p. 1936-1936
Abstract:
The Ge laser is one of the most promising devices as a monolithic light source for high-speed optical interconnections due to its compatibility with Si processes. Although optical gain has been observed [1, 2], further improvements of crystallinity are required [3, 4] to ensure continuous wave operation of Ge lasers. In this work, we fabricated high-quality Ge waveguides using epitaxial lateral overgrowth on a SiO 2 layer and chemical mechanical polishing [5] , and we investigated its crystallographic and optical properties. An eight-inch Si wafer was used as a substrate, and a SiO 2 window was fabricated as a mask for Ge selective epitaxial growth (SEG). A Ge layer was selectively grown by using low-pressure chemical vapor deposition along with germane (GeH 4 ) as a source of Ge with H 2 carrier gas. To prevent indirect transition by filling electrons into the L-valley in the conduction band of Ge [6], we also conducted in-situ phosphorus (P) doping by supplying phosphine (PH 3 ). First, a Ge buffer layer was deposited within the SiO 2 window at 400°C and annealed at 750°C, then an additional Ge layer was selectively grown only on the Ge buffer layer at relatively high temperature. Finally, rapid thermal annealing was carried out at 850°C. By optimizing the growth pressure, the length of the epitaxial lateral overgrowth (ELO) on the SiO 2 layer was increased to more than 5 mm. Although the dislocation and stacking faults were observed around a region of the Ge on the Si substrate by transmission electron microscopy, no dislocations were evident on the ELO-Ge region grown on the SiO 2 layer. Since the thickness of the SEG-Ge layer increased as the length of the ELO increased, chemical mechanical polishing (CMP) was applied to remove the top part of the SEG-Ge layer. By using measurements of micro-Raman spectroscopy, it was confirmed that the tensile strain was remained in the ELO-Ge on SiO 2 layer even after the CMP process. Then, additional P doping was carried out by spin-on-dopant (SOD) process. The SOD solution [Filmtronics, P8545SF] was coated on the CMP-Ge layer, and the annealed at 750°C, for 10min. The maximum P concentration of 3.2×10 19 cm -3 was achieved, which was measured by secondary ion mass spectroscopy. Finally, Ge waveguides (Ge-WGs) were fabricated by reactive ion etching of the CMP-Ge layer to remove a part of the Ge layer that contained a lot of crystal defects due to the lattice mismatch between Ge and Si. Figure 1(a) shows a bird's-eye SEM image of the Ge-WG after dry etching with an offset (Dx) of 3.1 mm to the SiO 2 window. Photoluminescence (PL) spectra from the Ge-WGs with various Dx are shown in Fig. 1(b). Obvious PL spectra were observed from the Ge-WGs with peak wavelength around 1600 nm. The PL peak intensity from the Ge-WG with Dx = 3.1 mm was four-times higher than that corresponding to Dx = 0.1 mm. This result indicates that the better crystallinity of the Ge-WG was obtained at the position apart from the Ge/Si interface. This work was supported by Project for Developing Innovation Systems of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. References [1] R. E. Camacho-Aguilera, et al., Optics Express 20 (2012) 11316. [2] R. Koerner, et al., Optics Express 23 (2015) 14815. [3] Q. Li, et al., Appl. Phys. Lett. 85 (2004) 1928. [4] H. -Y. Yu, et al., Electron Dev. Lett. 33 (2012) 579. [5] K. Oda, et al., Jpn. J. Appl. Phys. 55 (2016) 04EH06. [6] J. Liu, et al., Opt. Lett. 35 (2010) 679. Figure 1
Type of Medium:
Online Resource
ISSN:
2151-2043
DOI:
10.1149/MA2016-02/30/1936
Language:
Unknown
Publisher:
The Electrochemical Society
Publication Date:
2016
detail.hit.zdb_id:
2438749-6
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