Abstract
The anisotropic nature of carrier mobility in simple cubic crystalline semiconductors, such as technologically important silicon and germanium, is well understood as a consequence of effective mass anisotropy arising from a change in band structure along non-identical surface crystal directions. In contrast to this, we show experimentally that this type of anisotropy is not the dominant contribution. Recent advances in epitaxial growth of high quality germanium enabled the appearance of high mobility 2D carriers suitable for such an experiment. A strong anisotropy of 2D carrier mobility, effective mass, quantum, and transport lifetime has been observed, through measurements of quantum phenomena at low temperatures, between the ⟨110⟩ and ⟨100⟩ in-plane crystallographic directions. These results have important consequences for electronic devices and sensor designs and suggest similar effects could be observed in technologically relevant and emerging materials such as SiGe, SiC, GeSn, GeSnSi, and C (Diamond).
Highlights
The anisotropic nature of carrier mobility in simple cubic crystalline semiconductors, such as technologically important silicon and germanium, is well understood as a consequence of effective mass anisotropy arising from a change in band structure along non-identical surface crystal directions
Anisotropy of mobility in simple cubic semiconductors was first studied over 50 years ago,2–5 and experimentally observed for electrons in Ge,6 usually attributed to variations in band structure and effective mass along non-equivalent crystallographic orientations
Our recent study of a series of square devices containing Ge quantum well (QW) heterostructures concluded that wafer axis tilt resulted in significant 2D hole gas (2DHG) mobility anisotropy between nominally identical h110i directions
Summary
The anisotropic nature of carrier mobility in simple cubic crystalline semiconductors, such as technologically important silicon and germanium, is well understood as a consequence of effective mass anisotropy arising from a change in band structure along non-identical surface crystal directions. A strong anisotropy of 2D carrier mobility, effective mass, quantum, and transport lifetime has been observed, through measurements of quantum phenomena at low temperatures, between the h110i and h100i in-plane crystallographic directions.
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