GeSn alloys have emerged as a promising material for realizing CMOS-compatible light sources. GeSn lasers demonstrated to date have large device footprints and active areas, which limit the realization of densely integrated lasers operating at low power consumption. Thanks to their intrinsically small device form factors, 1D photonic crystal lasers may offer opportunities to overcome such limitations of large GeSn lasers. Here, we present a 1D photonic crystal nanobeam laser with a very small device footprint (~7 μm2) and a compact active area (~1.2 μm2) on a GeSn-on-insulator substrate.
Combining Sn alloying and tensile strain to Ge has emerged as the most promising engineering approach to create an efficient Si-compatible lasing medium. The residual compressive strain in GeSn has thus far made the simple geometrical strain amplification technique unsuitable for achieving tensile strained GeSn. Herein, by utilizing two unique techniques, we report the introduction of a uniaxial tensile strain directly into GeSn micro/nanostructures. By converting GeSn from indirect to direct bandgap material via tensile strain, we achieve a 10-fold increase in the light emission intensity.
In the quest for practical group IV lasers, researchers have proposed a few ideas such as strain engineering of Ge and alloying of Sn into Ge. Both approaches fundamentally alter bandstructure such that Ge can become a direct bandgap material. Recently, relaxation of limiting compressive strain and addition of mechanical tensile strain have been employed to improve the lasing performance. However, such strain engineering has thus far been possible only in suspended device configurations, which significantly limit heat dissipation and hinder the device performance. We herein demonstrate GeSn microdisk lasers fully released on Si that relax the limiting compressive strain and achieve excellent thermal conduction.
The potential for establishing energy gaps by pseudo-magnetic fields in strain-engineered graphene has sparked much interest recently. However, the limited sizes of induced pseudo-magnetic fields and the complicated platforms for straining graphene have thus far prevented researchers from harnessing the unique pseudo-magnetic fields in optoelectronic devices. In this work, we present an experimental demonstration of triaxially strained suspended graphene structures capable of obtaining quasi-uniform pseudo-magnetic fields over a large scale. The novel metal electrode design functions as both stressors and current injectors. We also propose a hybrid laser structure employing a 2D photonic crystal and triaxially strained graphene as an optical cavity and gain medium, respectively.
Pseudo-magnetic field in strained graphene has emerged as a promising route to allow observing intriguing physical phenomena that would be inaccessible with laboratory superconducting magnets. However, experimental observation of the impact of pseudo-magnetic field on optical and electrical properties of graphene has remained unknown. Here, using time-resolved infrared pump-probe spectroscopy, we provide unambiguous evidence of slow carrier dynamics enabled by a giant pseudo-magnetic field (~100 T) in periodically strained graphene. Our finding presents unforeseen opportunities towards harnessing the new physics of graphene in previously unachievable high magnetic field regimes.
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