Germanium (Ge) has a direct band gap (E0) of 0.81 eV at room
temperature; however, applying small perturbations to Ge can shift E0 to lower
energies resulting in dramatically improved performance for semiconductor and
telecommunication applications. Stressing Ge using tensile strain provides one
means by which to lower its E0, but the current best method requires depositing
the Ge on Silicon (Si) at relatively high temperatures and inducing stress
through the subsequent contraction of the Si. While this process provides
biaxial tensile strains as high as 0.25% in films as thick as 1 µm, higher
strain values are necessary for most optoelectronic applications, which require
tunable E0. Furthermore, the thermal expansion process lacks precise strain
control, offers limited maximum strain value (˜0.3%), and effectuates
undesirable inter-diffusion of the elements across the Si-Ge heterojunction.
Researchers at Arizona State University have developed an
improved method for preparing tensile strained Ge on semiconductor substrates.
Specifically, this method forms a tensile strained layer of Ge over a layer of
Ge1-ySny deposited on a semiconductor substrate using an admixture of (GeH3)2CH2
and Ge2H6 in a ratio of between 1:10 and 1:30. The tensile strained. The method
functions to tune the strain of the Ge epilayer by varying the buffer
composition.
Potential Applications
- Semiconductor Electronics (e.g. high-speed transistors,
back-end CMOS telecommunications, etc.)
- Optoelectronics (e.g. Optical Fiber Communications,
Lasers, etc.)
Benefits and Advantages
- Tunable Tensile Strains (between 0.15% and 0.45%) –
precise strain control for optoelectronic applications
- Increased Maximum Tensile Strain (high as 0.45% observed
compared to 0.3%) – necessary for viability in higher bands (e.g. U-Band)
- Operates at Substantially Lower Temperatures (growth
occurs at 350-380°C as opposed to 800-900°C) – reduces inter-diffusion of the
elements across the Si-Ge heterojunction; CMOS compatible
- Offers High-Quality, Thermally Stable Tensile Strained Ge
Layers (greater than 100 nm thick have been grown on Si(100) wafers)
- Exhibits Desirable Crystalline Geometry – perfectly
tetragonal structure, homogenous compositional and strain profiles, low
threading dislocation densities and atomically planar surfaces; optimal for
tuning applications
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