Holmes, Stuart Nicholas;
Gul, Yilmaz;
Pullen, Iwan;
Gough, J;
Thomas, Kalarikad;
Jia, Hui;
Tang, Mingchu;
... Pepper, Michael; + view all
(2024)
MBE growth of Ge1-xSnx devices with intrinsic disorder.
Journal of Physics D: Applied Physics
10.1088/1361-6463/ad5a1a.
(In press).
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Abstract
We discuss the electrical properties of MBE (molecular beam epitaxy) grown, modulation doped, Ge1-xSnx quantum well devices. A consequence of the epitaxial growth process is that electronic disorder is introduced even in modulation doped quantum well structures and electrical transport properties that are characteristic of a high level of disorder are apparent. MBE growth of this material also results in the surface segregation of elemental β-Sn in the way that has been observed utilizing other epitaxial growth methods. A thermally activated, p-type mobility is a clear feature of the electrical properties with generally temperature independent hole densities ~ 1012 cm-2 from the measured Hall effect and coming from the modulation doping. We present a discussion of Hall effect measurements in this disordered regime. The percolation carrier density in MBE modulation doped GeSn is in the region of ~ 1×1012 cm-2 although Hall measurements in this regime are difficult to quantify when the resistivity > (h/e2). In this notation h is Planck’s constant and e is the unit of charge. Conductivities (σ) as low as ~ 0.028×(e2/h)×square can be measured in the 4-contact ac configuration and the temperature dependence indicates a mobility edge in these p-type devices below ~ 2×1012 cm-2. At lower temperatures (< ~1 K) the presence of a Coulomb gap can be determined using dc transport, constant voltage measurements where small ac current excitation is not available experimentally. This 2-contact configuration can determine σ down to ~ 10-6×(e2/h), deep into the localization regime, revealing a hopping conductivity dominated system. We discuss the relevance of these electrical properties for MBE grown GeSn devices.
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