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. 2014 Nov 7:4:6964.
doi: 10.1038/srep06964.

Heterogeneous integration of epitaxial Ge on Si using AlAs/GaAs buffer architecture: suitability for low-power fin field-effect transistors

Mantu K Hudait  1 , Michael Clavel  1 , Patrick Goley  1 , Nikhil Jain  1 , Yan Zhu  1
Affiliations

Heterogeneous integration of epitaxial Ge on Si using AlAs/GaAs buffer architecture: suitability for low-power fin field-effect transistors

Mantu K Hudait et al. Sci Rep. .

Abstract

Germanium-based materials and device architectures have recently appeared as exciting material systems for future low-power nanoscale transistors and photonic devices. Heterogeneous integration of germanium (Ge)-based materials on silicon (Si) using large bandgap buffer architectures could enable the monolithic integration of electronics and photonics. In this paper, we report on the heterogeneous integration of device-quality epitaxial Ge on Si using composite AlAs/GaAs large bandgap buffer, grown by molecular beam epitaxy that is suitable for fabricating low-power fin field-effect transistors required for continuing transistor miniaturization. The superior structural quality of the integrated Ge on Si using AlAs/GaAs was demonstrated using high-resolution x-ray diffraction analysis. High-resolution transmission electron microscopy confirmed relaxed Ge with high crystalline quality and a sharp Ge/AlAs heterointerface. X-ray photoelectron spectroscopy demonstrated a large valence band offset at the Ge/AlAs interface, as compared to Ge/GaAs heterostructure, which is a prerequisite for superior carrier confinement. The temperature-dependent electrical transport properties of the n-type Ge layer demonstrated a Hall mobility of 370 cm(2)/Vs at 290 K and 457 cm(2)/Vs at 90 K, which suggests epitaxial Ge grown on Si using an AlAs/GaAs buffer architecture would be a promising candidate for next-generation high-performance and energy-efficient fin field-effect transistor applications.

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Figures

Figure 1
Figure 1. Schematic cross-section of the (a) Ge based nanoscale fin field-effect transistor structure on Si using a composite AlAs/GaAs metamorphic buffer architecture where the thickness of the Ge layer is the fin height and (b) the layer structure studied in this paper.
Figure 2
Figure 2. X-ray diffraction analysis of Ge on Si: (a) X-ray rocking curve from the 240 nm thick Ge grown on an Si substrate using an AlAs/GaAs buffer, (b) symmetric (004) reciprocal space map of the Ge/AlAs/GaAs/Si structure, (c) reciprocal lattice point of GaAs, Ge and AlAs layer precisely determined using triple axis proportional detector, and (d) asymmetric (115) reciprocal space map of the structure.
Figure 3
Figure 3
Cross-sectional TEM micrographs: (a) Cross-sectional TEM micrograph of the entire Ge/AlAs/GaAs/Si structure, high-resolution TEM micrograph of (b) Ge/AlAs and (c) AlAs/GaAs heterointerfaces. Sharp heterointerfaces between Ge/AlAs and AlAs/GaAs were demonstrated.
Figure 4
Figure 4. Band offsets using x-ray photoelectron spectroscopy: XPS spectra of (a) Ge 3d core level and valence band maximum, VBM from thick Ge film, (b) As 3d core level and VBM from thick AlAs film, (c) As 3d, Ge 3d core levels from ~1.5 nm Ge/AlAs interface, and (d) energy-band alignment of the Ge/AlAs heterointerface, respectively.
Figure 5
Figure 5. Hall mobility measurement: Hall mobility and the sheet carrier density as a function of the measurement temperature from 90 K to 315 K.
The mobility values are comparable with the bulk mobility values of Ge at this measured carrier concentration.
See this image and copyright information in PMC

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