The deeply depleted graphene-insulator-semiconductor (D2GOS) junction has been shown to be a promising device structure for photon detection, due to its high responsivity, signal to noise ratio and ability for direct readout of individual pixels. One of the unique advantages of this architecture is its ease of exchangeability to other semiconductor absorber material, with the major caveat of realizing a functional device is to be able to deplete the semiconductor in the graphene-insulator-semiconductor (GOS) stack. This allows the opportunity to design GOS junctions to selective absorption cutoffs by choosing bulk semiconductors with the appropriate bandgaps. In this work, recent progress in demonstrating the D2GOS detectors across the mid-Infrared to gamma ray spectrum is discussed, using a variety of semiconductor absorbers (InSb, InAs, InGaAs, Si, and CdZnTe), along with the challenges associated with working with each absorber type. It is shown that the semiconductor/insulator interface defect density and graphene mobility are the two critical determinants in improving the D2GOS junction’s integration lifetime, responsivity and signal to noise ratio. Reduction of defects the semiconductor/insulator interface are demonstrated by employing surface passivation of the semiconductor through the deposition of a thin high-quality oxide, specific to each semiconductor. This is shown to dramatically reduce the dark charge generation in the device, resulting in improvements in integration lifetime, responsivity and signal to noise ratio. Finally, the device performance between 77 K and 300 K are compared, demonstrating an increase in performance at lower temperatures, due to further reduction of dark charge generation.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Metasurfaces have been investigated for various applications ranging from beam steering, focusing, to polarization conversion. Along with passive metasurfaces, significant efforts are also being made to design metasurfaces with tunable optical response. Among various approaches, voltage tuning is of particular interest because it creates the possibility of integration with electronics. In this work, we demonstrate voltage tuning of reflectance from a complementary metasurface strongly coupled to an epsilon-near-zero (ENZ) mode in an ultrathin semiconductor layer. Our approach involves electrically controlling the carrier concentration of the ENZ layer to modulate the polaritonic coupling between the dipole resonances of the metasurface and the ENZ mode for modulating the reflectance of the metasurface. The hybrid structure we fabricate is similar to MOSCAP configuration where the complementary metasurface offers a continuous gold top layer for biasing and positive/negative bias to the metasurface leads to accumulation/depletion of carriers in the ENZ layer beneath it. We optimized our structure by using InGaAs as the ENZ material because of its high mobility and low effective mass. This allowed us to reduce the doping requirement and thereby reduce the ionized impurity scattering as well as the reverse bias required to deplete the ENZ layer. For low leakage and efficient modulation of carrier density, we used Hafnia as the gate dielectric. We further added a reflecting backplane below the ENZ layer to enhance the interaction and by applying bias, we achieved spectral shifts of 500 nm and amplitude modulation of 11% of one of the polariton branches at 14 µm.
Coupling of metasurfaces to intersubband transitions (ISTs) in semiconductor quantum wells (QWs) has been extensively studied for various applications ranging from generating giant nonlinear optical response to designing tunable metasurfaces for applications such as ultrafast spatial optical modulators and voltage tunable filters. In this work, we experimentally demonstrate a fundamentally new approach of actively controlling the coupling of ISTs in QWs to a metasurface for voltage tuning its optical response. Unlike previous approaches, we use voltage-controlled quantum tunneling to control the carrier concentration in the QWs for turning on/off the ISTs. We design a multi-quantum well structure consisting of four undoped InGaAs wells with AlInAs barriers grown on top of a highly doped InGaAs layer that acts as an electron reservoir. The heterostructure is optimized such that the first IST in all the wells is at 11µm. A complementary gold metasurface with dipole resonances at 11µm is fabricated on top of the QW structure. We designed the heterostructure such that by applying a bias of 1V, the energy bands of all the QWs get aligned simultaneously, leading to the occupation of the ground state of all the QWs via quantum tunneling of the electrons from the electron reservoir. The ISTs which were turned off due to negligible electron density gets turned on at 1V, and this leads to coupling between the ISTs and the dipoles resonances of the metasurface. The voltage induced coupling leads to reflectance modulation which we confirmed experimentally by rapid scan double modulation FTIR measurements.
Three dimensional pillared graphene nanostructures were grown on metal substrates through a one-step chemical vapor
deposition (CVD) by introducing a mixture precursor gases (H2, C2H4). We further explored sputtering evaporation system to uniformly deposited a layer of amorphous silicon on the as grown 3D carbon nanostructure. The surface morphologies of the carbon-silicon nanocomposites were investigated by scanning electron microscopy (SEM). Cyclic
voltammetry and charge-discharge are conducted to determine the performance of the 3D hybrid carbon-silicon
nanostructure for lithium ion battery anode.
Graphene’s unique mechanical, electrical, and thermal properties have made it a very attractive material desired for use in future technologies. Over the recent years, there have been many breakthroughs in research on graphene. Recently, the focus of the latest research has shifted towards scaling graphene production for commercial use by industry. The most promising method for scaling graphene growth for industry usage is chemical vapor deposition (CVD). CVD is a low cost, economic and scalable method for producing graphene. However, consistently producing high quality graphene quickly on a large scale has eluded researchers. Here we detail a method for reducing growth time required to produce high quality, large area graphene by adjusting the fluid mechanics of the CVD.
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