Abstract
While light-emitting nanostructures composed of group-IV materials fulfil the mandatory compatibility with CMOS-fabrication methods, factors such as the structural stability of the nanostructures upon thermal annealing, and the ensuing photoluminescence (PL) emission properties, are of key relevance. In addition, the possibility of improving the PL efficiency by suitable post-growth treatments, such as hydrogen irradiation, is important too. We address these issues for self-assembled Ge quantum dots (QDs) that are co-implanted with Ge ions during their epitaxial growth. The presence of defects introduced by the impinging Ge ions results in pronounced PL-emission at telecom wavelengths up to room temperature (RT) and above. This approach allows us to overcome the severe limitations of light generation in the indirect-band-gap group-IV materials. By performing in-situ annealing, we demonstrate a high PL-stability of the defect-enhanced QD (DEQD) system against thermal treatment up to 600 °C for at least 2 h, even though the Ge QDs are structurally affected by Si/Ge intermixing via bulk diffusion. The latter, in turn, allows for emission tuning of the DEQDs over the entire telecom wavelength range from 1.3 µm to 1.55 µm. Two quenching mechanisms for light-emission are discussed; first, luminescence quenching at high PL recording temperatures, associated with the thermal escape of holes to the surrounding wetting layer; and second, annealing-induced PL-quenching at annealing temperatures >650 °C, which is associated with a migration of the defect complex out of the QD. We show that low-energy ex-situ proton irradiation into the Si matrix further improves the light emission properties of the DEQDs, whereas proton irradiation-related optically active G-centers do not affect the room temperature luminescence properties of DEQDs.
Highlights
Practical, Si-compatible, monolithically-integrated lasers are the main missing ingredient towards the realization of efficient and low-cost integrated silicon photonics circuits that are designated to uplift fields of on-chip data communication [1,2,3] and on-chip sensing [4]
The defect-enhanced quantum dot (QD) (DEQD) samples were grown in a SIVA-45 molecular beam epitaxy (MBE) system (RIBER, Paris, France) on high-resistivity (>5000 Ωcm) Si(001) substrates
These results suggest that it is this interstitial defect and the surrounding distorted crystal that are responsible for the enhanced light-emission properties of DEQDs at room temperature
Summary
Si-compatible, monolithically-integrated lasers are the main missing ingredient towards the realization of efficient and low-cost integrated silicon photonics circuits that are designated to uplift fields of on-chip data communication [1,2,3] and on-chip sensing [4]. Of the fabrication method used, the stability of the light emission with respect to the typical thermal budget of a CMOS process is of key importance. Concerning fast communication, monolithic light sources have the distinct advantage of possible front-end integration, i.e., placing the photonics layer in-between the CMOS and the metallization layers. For front-end integration, the thermal budget of the photonics layer, including the fabrication of the light-emitters, must not deteriorate the underlying CMOS layer
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