C-V - and DLTS-investigations of pyramid-shaped Ge Quantum Dots embedded in n-type Silicon

摘要

We investigate self-assembled pyramid-shaped Ge Quantum Dots (QDs) with lateral dimensions of 15 nm, and heights of 2.5-3 nm. These Ge QDs were grown by Molecular Beam Epitaxy (MBE) on n-type Si(100) substrates using the Sb-mediated growth mode. The resistivity of the substrates was about 5 cm. The Si buffer layer below the QDs and the Si capping layer above them were doped up to 10~(18) cm~(-3) by Sb. Cross-section transmission electron microscopy shows the QDs and the Sb delta-doped layers. Using standard photolithographic techniques, a 0.3 mm~2 Au Schottky contact was applied to the epilayer, while an Ohmic contact was formed on the back side of the substrate. Plotting C~(-2) vs. V plot reveals the nominal doping of 10~(18) cm~(-3). DLTS studies revealed two levels with fitted activation energies of 49 meV and 360-390 meV. They are related to the Sb doping and the Pb interface states, respectively. The simulation suggests a deep level with a volumetric concentration of 2.55×10~(15) cm~(-3). Multiplying this value by the thickness of the depletion region obtained from the CV measurements, we find that the deep level capture about 5.8×10~9 electrons per cm~2.