• Oehme, Michael
• Weißhaupt, David
• Kasper, Erich
• Schwarz, Daniel
• Hersperger, Tim
• Wanitzek, Maurice
• Sigle, Eric

Abstract

<jats:title>Abstract</jats:title><jats:p>Two-dimensional hole gases are demonstrated in modulation doped Si<jats:italic><jats:sub>x</jats:sub></jats:italic>Ge<jats:sub>1−<jats:italic>x</jats:italic>−<jats:italic>y</jats:italic></jats:sub>Sn<jats:italic><jats:sub>y</jats:sub></jats:italic> quantum wells (QWs), which are embedded in Si<jats:sub>0.2</jats:sub>Ge<jats:sub>0.8</jats:sub> barrier layers. The modulation doped QW structures are fabricated with molecular beam epitaxy on a thin (100 nm) virtual SiGe substrate on a (001) oriented Si substrate. The virtual substrate (VS) concept utilizes the Si diffusion into an as- grown thin, strain relaxed Ge layer during a following annealing step. The lateral lattice spacing of the SiGe-VS could be varied by the annealing temperature in the range between 830 °C and 860 °C. Half-hour anneal at 848 °C results in nearly strain free growth for the following Si<jats:sub>0.2</jats:sub>Ge<jats:sub>0.8</jats:sub> barrier layer. Boron doping above an undoped 10 nm spacer on top of the 15 nm QW provides a reservoir for hole transfer from the barrier to the well. Electrical conductivity, sheet hole density ps and mobility are measured as function of temperature. In all investigated Si<jats:italic><jats:sub>x</jats:sub></jats:italic>Ge<jats:sub>1−<jats:italic>x</jats:italic>−<jats:italic>y</jats:italic></jats:sub>Sn<jats:italic><jats:sub>y</jats:sub></jats:italic> channels the Hall measurements show the typical freeze out of holes outside the QW. Alloy scattering dominates the low-temperature mobility by adding Sn or Si to the Ge reference well. A linear relationship for the charge transfer from the modulation doping into the undoped Si<jats:italic><jats:sub>x</jats:sub></jats:italic>Ge<jats:sub>1−<jats:italic>x</jats:italic>−<jats:italic>y</jats:italic></jats:sub>Sn<jats:italic><jats:sub>y</jats:sub></jats:italic> channel as function of the lattice mismatch between the channel material and the matrix material could be found at low-temperatures (8 K). An analytical model for this charge transfer confirms the nearly linear relationship by considering the triangular shape of the potential in modulation doped QW structures.</jats:p>

Topics

• density
• mobility
• Boron
• two-dimensional
• annealing
• electrical conductivity