On the process of hole trapping in Ge/Si heterostructures with Ge quantum dots

Admittance spectroscopy is used to determine the cross sections and energy levels of holes in Ge/Si heterostructures with Ge quantum dots. The structures are grown by molecular-beam epitaxy. It is established that, in layers of quantum dots produced at low growth temperatures $T_g\le$ 450$^\circ$C, the capture cross section for hole trapping into quantum dots exponentially increases with increasing hole binding energy (the Meyer–Neldel rule), with the same characteristic energy $\sim$ 25 eV independent of $T_g$. It is shown that the Meyer-Neldel rule is violated in structures grown at higher temperatures or in samples treated in hydrogen plasma. In the case of nanoclusters synthesized at low temperatures, the experimental results suggest that charge-carrier trapping into Ge quantum dots proceeds via the electron-phonon mechanism with the participation of structural defects.