Observation of inter-sub-level transitions in modulation-doped Ge quantum dots

The inter-sub-level transitions in modulation-doped Ge quantum dots are observed. The dot structure is grown by molecular-beam epitaxy, and consists of 30 periods of Ge quantum dots sandwiched by two 6 nm boron-doped Si layers. An absorption peak in the midinfrared range is observed at room temperature by Fourier transform infrared spectroscopy, which is attributed to the transitions between the first two heavy-hole states of the Ge quantum dots. This study suggests the possible use of modulation-doped Ge quantum dots for improved infrared detector applications.