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Direct bandgap group IV materials could provide intimate integration of lasers, amplifiers, and compact modulators within complementary metal–oxide–semiconductor for smaller, active silicon photonics. Dilute germanium carbides (GeC) with ∼1 at. % C offer a direct bandgap and strong optical emission, but energetic carbon sources such as plasmas and e-beam evaporation produce defective materials. In this work, we used CBr4 as a low-damage source of carbon in molecular beam epitaxy of tin-free GeC, with smooth surfaces and narrow x-ray diffraction peaks. Raman spectroscopy showed substitutional incorporation of C and no detectable sp2 bonding from amorphous or graphitic carbon, even without surfactants. Photoluminescence shows strong emission compared with Ge.

 

GeSnC alloys offer a route to direct bandgap semiconductors for CMOS-compatible lasers, but the use of CBr4 as a carbon source was shown to reduce Sn incorporation by 83%–92%. We report on the role of thermally cracked H in increasing Sn incorporation by 6x–9.5x, restoring up to 71% of the lost Sn, and attribute this increase to removal of Br from the growth surface as HBr prior to formation of volatile groups such as SnBr4. Furthermore, as the H flux is increased, Rutherford backscattering spectroscopy reveals a monotonic increase in both Sn and carbon incorporation. X-ray diffraction reveals tensile-strained films that are pseudomorphic with the substrate. Raman spectroscopy suggests substitutional C incorporation; both x-ray photoelectron spectroscopy and Raman suggest a lack of graphitic carbon or its other phases. For the lowest growth temperatures, scanning transmission electron microscopy reveals nanovoids that may account for the low Sn substitutional fraction in those layers. Conversely, the sample grown at high temperatures displayed abrupt interfaces, notably devoid of any voids, tin, or carbon-rich clusters. Finally, the surface roughness decreases with increasing growth temperature. These results show that atomic hydrogen provides a highly promising route to increase both Sn and C to achieve a strongly direct bandgap for optical gain and active silicon photonics.

 

In this opinion we trace the evolution of the quantum dot mid-infrared photodetector, from epitaxially-grown self-assembled quantum dot detectors, to a new generation of colloidal nano-crystal based devices. We opine on the advantages and challenges associated with these colloidal quantum dot materials and discuss their potential for commercial device applications.

 

We present a transient response study of a semiconductor based plasmonic switch. The proposed device operates through active control and modulation of localized electron density waves, i.e., surface plasmon polaritons (SPPs) at degenerately doped In_0.53Ga_0.47As based PN⁺⁺junctions. A set of devices is designed and fabricated, and its optical and electronic behaviors are studied both experimentally and theoretically. Optical characterization shows far-field reflectivity modulation, a result of electrical tuning of the SPPs at the PN⁺⁺junctions for mid-IR wavelengths, with significant 3 dB bandwidths. Numerical studies using a self-consistent electro-optic multi-physics model are performed to uncover the temporal response of the devices’ electromagnetic and kinetic mechanisms facilitating the SPP switching at the PN⁺⁺junctions. Numerical simulations show strong synergy with the experimental results, validating the claim of potential optoelectronic switching with a 3 dB bandwidth as high as 2 GHz. Thus, this study confirms that the presented SPP diode architecture can be implemented for high-speed control of SPPs through electrical means, providing a pathway toward fast all-semiconductor plasmonic devices.

 

We demonstrate a room-temperature all-epitaxial guided-mode resonance light-emitting diode operating in the mid-wave infrared. The device comprises a dielectric waveguide with an AlGaAsSb p−i−n diode core, below a layer of grating-patterned GaSb and above a highly doped, and thus, low index, InAsSb layer. Light emitted from the device active region into propagating modes in the waveguide scatters into free space via the GaSb grating, giving rise to spectrally narrow features that shift with emission angle across much of the mid-wave infrared. For collection angles approaching 0°, we are able to obtain linewidths of ∼2.4 meV across the spectral/angular emission of the LED, corresponding to λ/Δλ∼570. Fine control of emission wavelength can be achieved by tuning the applied current, which causes a redshift of approximately 20 nm due to the thermo-optic effect. The presented device has the potential for use in compact, high bandwidth, and low-cost mid-wave infrared sensing applications requiring spectral discrimination.

 

We demonstrate efficient filtering of coherent light from a broad spectral background. A Michelson interferometer is used to effectively filter out the coherent emission of mid-infrared lasers from the co-propagating incoherent emission of a broadband thermal source. We show coherent light suppression as high as 16.9 dB without any modification of the broadband incoherent background spectrum. In addition, we demonstrate the ability to measure the spatially dependent (incoherent) thermal emission from a patterned surface, using our filter to remove a coherent signal which would otherwise overload our detection system. The demonstrated filter is rapidly tunable and wavelength-flexible, and has potential for imaging and spectroscopy applications in the presence of an otherwise overpowering coherent signal.

 

Optoelectronic devices in the mid-infrared have attracted significant interest due to numerous potential applications in communications and sensing. Molecular beam epitaxial (MBE) growth of highly doped InAs has emerged as a promising “designer metal” platform for the plasmonic enhancement of mid-infrared devices. However, while typical plasmonic materials can be patterned to engineer strong localized resonances, the lack of lateral control in conventional MBE growth makes it challenging to create similar structures compatible with monolithically grown plasmonic InAs. To this end, we report the growth of highly doped InAs plasmonic ridges for the localized resonant enhancement of mid-IR emitters and absorbers. Furthermore, we demonstrate a method for regaining a planar surface above plasmonic corrugations, creating a pathway to epitaxially integrate these structures into active devices that leverage conventional growth and fabrication techniques.