Hole emission from self-organized Ge quantum dots with a diameter of ∼70 nm in a Si matrix is investigated by time-resolved capacitance spectroscopy [deep level transient spectroscopy (DLTS)]. A complex DLTS signal is observed and explained in terms of thermally activated emission from localized many-particle states. In particular, a gradually decreasing activation energy is found with increasing hole population. A qualitative understanding of the DLTS signal and the observed activation energies is achieved in terms of many-particle states determined by quantization and Coulomb charging.

Crystalline SiGe alloy sheet polymers were topotactically prepared from epitaxially grown calcium germanosilicide Ca(Si1−xGex)2 precursor films in the whole composition range. These polygermanosilynes are found to be a well-defined mixture of the known siloxene and polygermyne sheet polymers with the OH groups exclusively bonded to silicon. The optical properties determined by photoluminescence and optical reflection measurements identify the mixed SiGe sheet polymers as direct semiconductors with efficient luminescence tunable in the energy range between 2.4 and 1.3 eV.

Intra-valence band photocurrent investigations of self-assembled Ge dots in Si are reported. Boron-doped Ge dots of about 70 nm diameter and 6.5 nm height are deposited by molecular beam epitaxy in the Stranski–Krastanov growth mode within the intrinsic region of a p+-i-p+ Si structure. For a broad excitation wavelength range between about 2 μm (620 meV) and 6 μm (207 meV), interlevel photocurrent is observed in normal incidence and waveguide geometry. The absorption is attributed to transitions from hole states bound in the Ge dots to continuum states. The photocurrent can be measured up to T=100 K without any significant decrease of the responsivity.