We show that a significant enhancement of the direct band gap photoluminescence can be achieved at room temperature in bulk Ge and Ge-on-insulator heavily n-doped by gas immersion laser doping. The photoluminescence signal from bulk Ge and Ge-on-insulator increases with the donor concentration. An enhancement factor of 20 as compared to the undoped material is achieved near the 1550 nm wavelength for active dopant concentrations around 5 ϫ 10 19 cm −3. These results are supported by calculations of the Ge spontaneous emission spectrum taking into account the doping effect on the electron distribution in the direct and indirect conduction band valleys.

Intersubband electroluminescence from strain-compensated Si/Si0.2Ge0.8 quantum cascade (QC) structures, consisting of up to 30 periods grown by molecular beam epitaxy on Si0.5Ge0.5 pseudosubstrates is reported. The design of the active region is based on a so-called “bound-to-continuum transition.” The intersubband radiation is emitted at a wavelength of 7 μm and is polarized, as expected for intersubband transitions between heavy hole states. A good agreement with photocurrent measurements is also found.

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We have investigated the photoluminescence of single and multiple layers of Ge/Si self-assembled quantum dots as a function of the excitation power density. We show that the photoluminescence of the quantum dots is strongly dependent on the pump excitation power. The photoluminescence broadens and is blueshifted by as much as 80 meV as the power excitation density increases. Meanwhile, the photoluminescence associated with the two-dimensional wetting layers exhibits only a weak dependence on the pump excitation power. This significant blueshift is interpreted in terms of state filling and recombination from the confined excited hole states in the dots. The photoluminescence data are correlated to the density of states as calculated by solving the three-dimensional Schrödinger equation in these islands with a lateral size of the order of 100 nm.

We have investigated the quality factors of silicon-based photonic crystal nanocavities using the photoluminescence of a single layer of Ge/Si self-assembled islands as an internal source. We focus on membrane-type L3 elongated cavities with or without their lateral edge air holes shifted in position. The photoluminescence measurements are performed at room temperature. We show that the quality factor of the fundamental mode observed at a normalized frequency u = a/lambda~_ 0.25 is strongly dependent on the incident pump power. This dependence is associated with the free-carrier absorption of the photogenerated carriers. The slope of the quality factor vs. incident pump power gives access to the carrier recombination dynamics in these Si-based nanocavities. The measurements indicate that the carrier dynamics is controlled by nonradiative recombination associated with surface recombinations. A surface recombination velocity of 4.8 x 10(4) cm/s is deduced from the experiments. The spectral red-shift of the cavity modes as a function of incident pump power is correlated to the temperature rise due to thermo-optic effects. The measured temperature rise, which can reach 190 K, is correlated to the value estimated by a thermal analysis.