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The electronic structures of three highly mismatched alloys (HMAs)—GeC(Sn), Ga(In)NAs, and BGa(In)As—were studied using density functional theory with HSE06 hybrid functionals, with an emphasis on the local environment near the mismatched, highly electronegative atom (B, C, and N). These alloys are known for their counterintuitive reduction in the bandgap when adding the smaller atom, due to a band anticrossing (BAC) or splitting of the conduction band. Surprisingly, the existence of band splitting was found to be completely unrelated to the local displacement of the lattice ions near the mismatched atom. Furthermore, in BGaAs, the reduction in the bandgap due to BAC was weaker than the increase due to the lattice constant, which has not been observed among other HMAs but may explain differences among experimental reports. While local distortion in GeC and GaNAs was not the cause for BAC, it was found to enhance the bandgap reduction due to BAC. This work also found that mere contrast in electronegativity between neighboring atoms does not induce BAC. In fact, surrounding the electronegative atom with elements of even smaller electronegativity than the host (e.g., Sn or In) consistently decreased or even eliminated BAC. For a fixed composition, moving Sn toward C and In toward either N or B was always energetically favorable and increased the bandgap, consistent with experimental annealing results. Such rearrangement also delocalized the conduction band wavefunctions near the mismatched atom to resemble the original host states in unperturbed Ge or GaAs, causing the BAC to progressively weaken. These collective results were consistent whether the mismatched atom was a cation (N), anion (B), or fully covalent (C), varying only with the magnitude of its electronegativity, with B having the least effect. The effects can be explained by charge screening of the mismatched atom's deep electrostatic potential. Together, these results help explain differences in the bandgap and other properties reported for HMAs from different groups and provide insight into the creation of materials with designer properties. 

Single-photon avalanche diodes (SPADs) that are sensitive to photons in the Short-wave infrared and extended short-wave infrared (SWIR and eSWIR) spectra are important components for communication, ranging, and low-light level imaging. The high gain, low excess noise factor, and widely tunable bandgap of Al_xIn_1-xAs_ySb_1-yavalanche photodiodes (APDs) make them a suitable candidate for these applications. In this work, we report single-photon-counting results for a separate absorption, charge, and multiplication (SACM) Geiger-mode SPAD within a gated-quenching circuit. The single-photon avalanche probabilities surpass 80% at 80 K, corresponding with single-photon detection efficiencies of 33% and 12% at 1.55 µm and 2 µm, respectively. 

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 report the theoretical prediction and experimental realization of the optical phenomenon of “ballistic resonance.” This resonance, resulting from the interplay between free charge motion in confining geometries and periodic driving electromagnetic fields, can be utilized to achieve negative permittivity at frequencies well above the bulk plasma frequency. As a proof of principle, we demonstrate all-semiconductor hyperbolic metamaterials operating at frequencies 60% above the plasma frequency of the constituent doped semiconductor “metallic” layer. Ballistic resonance will therefore enable the realization and deployment of various applications that rely on local field enhancement and emission modulation, typically associated with plasmonic materials, in new materials platforms. 

Remarkable systems have been reported recently using the polylithic integration of semiconductor optoelectronic devices and plasmonic materials exhibiting epsilon-near-zero (ENZ) and negative permittivity. In traditional noble metals, the ENZ and plasmonic response is achieved near the metal plasma frequency, limiting plasmonic optoelectronic device design flexibility. Here, we leverage an all-epitaxial approach to monolithically and seamlessly integrate designer plasmonic materials into a quantum dot light emitting diode, leading to a $5.6\times <\#comment/>$enhancement over an otherwise identical non-plasmonic control sample. The device presented exhibits optical powers comparable, and temperature performance far superior, to commercially available devices. 

Abstract A preliminary measurement of the second‐order nonlinear optical susceptibility of symmetric, coupled, InAs/AlSb multiple quantum well (MQW) structures is acquired through optical second‐harmonic generation (SHG) at fundamental wavelength 1.55 µm. High quality crystalline MQW structures of variable thickness and corresponding bulk AlSb control samples are achieved using a digital alloy epitaxial growth technique that avoids cluster formation and phase segregation. All samples are grown in between a GaSb cap and substrate layer. To isolate SHG from the MQW (or control) layers of interest from cap and substrate contributions, a multilayer optical response matrix model is built and independently tested by accurately reproducing linear reflectivity spectra. While a simplified response matrix analysis of SHG based solely on bulk χ⁽²⁾s does not reproduce the distinct SHG responses of the two sets of samples, the inclusion of an additional interface SHG contribution leads to a successful fit of the data and implies . The results demonstrate a proof‐of‐concept quantification of χ⁽²⁾in symmetric MQWs and suggest the possibility of engineering χ⁽²⁾in these structures, particularly with the introduction of well asymmetries.