Maria Makarova

Strong enhancement of direct transition photoluminescence with highly tensile-strained Ge grown by molecular beam epitaxy

Highly tensile-strained layers of Ge were grown via molecular beam epitaxy using step-graded InxGa1−xAs buffer layers on (100) GaAs. These layers have biaxial tensile-strain of up to 2.33%, have surface roughness of <1.1 nm, and are of high quality as seen with transmission electron microscopy. Low-temperature photoluminescence (PL) suggests the existence of direct-bandgap Ge when the strain is greater than 1.7%, and we see a greater than 100× increase in the PL intensity of the direct transition with 2.33% tensile-strain over the unstrained case. These results show promise for the use of tensile-strained Ge in optoelectronics monolithically integrated on Si.

Enhanced light emission in photonic crystal nanocavities with Erbium-doped silicon nanocrystals

Photonic crystal nanocavities are fabricated in silicon membranes covered by thermally annealed silicon-rich nitride films with Erbium-doped silicon nanocrystals. Silicon nitride films were deposited by sputtering on top of silicon on insulator wafers. The nanocavities were carefully designed in order to enhance emission from the nanocrystal sensitized Erbium at the 1540nm wavelength. Experimentally measured quality factors of ∼6000 were found to be consistent theoretical predictions. The Purcell factor of 1.4 was estimated from the observed 20-fold enhancement of Erbium luminescence.

Linewidth narrowing and Purcell enhancement in photonic crystal cavities on an Er-doped silicon nitride platform.

Light emission from Er-doped amorphous silicon nitride coupled to photonic crystal resonators is studied. The results demonstrate Purcell enhanced Er absorption and linewidth narrowing of the cavity resonance with increasing pump power.

Observation of Transparency of Erbium-doped Silicon nitride in photonic crystal nanobeam cavities

One dimensional nanobeam photonic crystal cavities are fabricated in an Er-doped amorphous silicon nitride layer. Photoluminescence from the cavities around 1.54 microm is studied at cryogenic and room temperatures at different optical pump powers. The resonators demonstrate Purcell enhanced absorption and emission rates, also confirmed by time resolved measurements. Resonances exhibit linewidth narrowing with pump power, signifying absorption bleaching and the onset of stimulated emission in the material at both 5.5 K and room temperature. We estimate from the cavity linewidths that Er has been pumped to transparency at the cavity resonance wavelength.

Photonic Crystal and Plasmonic Silicon-Based Light Sources

Efficient silicon (Si)-compatible emitters can realize inexpensive light sources for a variety of applications. In this paper, we study both photonic crystal (PC) and plasmonic nanocavities that enhance the emission of Si-compatible materials. In particular, we examine the coupling of silicon nanocrystals (Si-NCs) to silicon nitride PC cavities and Si-NCs in silicon dioxide to plasmonic gratings, both for enhancement of emission in the visible wavelengths. In addition, we also observe the enhancement of the 1530 nm emission from erbium-doped silicon nitride films coupled to Si PC cavities. Finally, we analyze the loss mechanisms associated with the hybrid silicon nitride/silicon system, and propose advancements in the designs of PC and plasmonic cavities for the emitters described in this paper.

Linewidth narrowing and Purcell enhancement in photonic crystal cavities on an Er-doped silicon nitride platform

Light emission from Er-doped amorphous silicon nitride coupled to photonic crystal resonators is studied. The results demonstrate Purcell enhanced Er absorption and linewidth narrowing of the cavity resonance with increasing pump power.

Two-dimensional porous silicon photonic crystal light emitters

We present design and fabrication of two-dimensional photonic crystal cavities made in nanoporous silicon luminescent at 700-800 nm. Enhancement in photoluminescence extraction efficiency at the resonant wavelength is expected due to Purcell effect.

Linewidth narrowing and luminescence enhancement in photonic crystal cavities and plasmonic gratings on an Er-doped silicon nitride platform

Light emission at 1.54 μm from an Er-doped amorphous silicon nitride layer coupled to photonic crystal resonators and plamonic arrays is studied. We observe the cavity resonances at cryogenic and room temperatures and under varying optical pump powers. The results demonstrate that small mode volume, high quality factor resonators enhance Er absorption rates dramatically at the cavity resonance. Photonic crystal cavity resonances exhibit linewidth narrowing with pump power at cryogenic temperatures, signifying absorption bleaching and partial inversion of the Er ions. In addition, we fabricate periodic metal-insulator-metal plasmonic structures with a simple bottom-up fabrication technique. We observe a factor of 10 increase of Er emission coupled to plasmonic structures.

Direct band gap tensile-strained Germanium

We report up to 2.3% biaxial tensile-strained Ge layers grown on InGaAs/GaAs buffer layers. Low-temperature photoluminescence shows a dramatic intensity increase for ≫2% tensile strained Ge, confirming the existence of a direct band gap Ge.

Efficient luminescence in highly tensile-strained germanium

Up to 2.3% biaxial tensile-strained Ge layers have been grown on InGaAs/GaAs buffer layers. A dramatic increase in low temperature photoluminescence intensity for >2% strained Ge confirms the existence of a direct band gap Ge.