Tensile strained direct bandgap GeSn microbridges enabled in GeSn-on-insulator substrates with residual tensile strain.

Despite having achieved drastically improved lasing characteristics by harnessing tensile strain, the current methods of introducing a sizable tensile strain into GeSn lasers require complex fabrication processes, thus reducing the viability of the lasers for practical applications. The geometric strain amplification is a simple technique that can concentrate residual and small tensile strain into localized and large tensile strain. However, the technique is not suitable for GeSn due to the intrinsic compressive strain introduced during the conventional epitaxial growth.

Strain-relaxed GeSn-on-insulator (GeSnOI) microdisks.

GeSn alloys offer a promising route towards a CMOS compatible light source and the realization of electronic-photonic integrated circuits. One tactic to improve the lasing performance of GeSn lasers is to use a high Sn content, which improves the directness. Another popular approach is to use a low to moderate Sn content with either compressive strain relaxation or tensile strain engineering, but these strain engineering techniques generally require optical cavities to be suspended in air, which leads to poor thermal management.

Pseudo-magnetic field-induced slow carrier dynamics in periodically strained graphene.

The creation of pseudo-magnetic fields in strained graphene has emerged as a promising route to investigate intriguing physical phenomena that would be unattainable with laboratory superconducting magnets. The giant pseudo-magnetic fields observed in highly deformed graphene can substantially alter the optical properties of graphene beyond a level that can be feasible with an external magnetic field, but the experimental signatures of the influence of such pseudo-magnetic fields have yet to be unveiled. Here, using time-resolved infrared pump-probe spectroscopy, we provide unambiguous evidence for slow carrier dynamics enabled by the pseudo-magnetic fields in periodically strained graphene.

Biaxially strained germanium crossbeam with a high-quality optical cavity for on-chip laser applications.

The creation of CMOS compatible light sources is an important step for the realization of electronic-photonic integrated circuits. An efficient CMOS-compatible light source is considered the final missing component towards achieving this goal. In this work, we present a novel crossbeam structure with an embedded optical cavity that allows both a relatively high and fairly uniform biaxial strain of ∼0.

Strained germanium nanowire optoelectronic devices for photonic-integrated circuits.

Strained germanium nanowires have recently become an important material of choice for silicon-compatible optoelectronic devices. While the indirect bandgap nature of germanium had long been problematic both in light absorption and emission, recent successful demonstrations of bandstructure engineering by elastic strain have opened up the possibility of achieving direct bandgap in germanium, paving the way towards the realization of various high-performance optical devices integrated on a silicon platform. In particular, the latest demonstration of a low-threshold optically pumped laser in a highly strained germanium nanowire is expected to vitalize the field of silicon photonics further.

Low-threshold optically pumped lasing in highly strained germanium nanowires.

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system.