High-optical-quality nanosphere lithographically formed InGaAs quantum dots using molecular beam epitaxy assisted GaAs mass transport and overgrowth

Optically active, highly uniform, cylindrical InGaAs quantum dot ͑QD͒ arrays have been fabricated using nanosphere lithography combined with Bromine ion-beam-assisted etching and molecular beam epitaxy ͑MBE͒-assisted GaAs mass transport. Previously fabricated QD nanopillar arrays showed significant degradation of optical properties due to the etch damage. Here, a novel mass transport process in a Riber 3200 was performed to encapsulate the lithographically defined InGaAs disk QDs in a GaAs matrix, resulting in the passivation of the etch-damaged QD sidewall layer. Photoluminescence emission intensity following the mass transport process increased by a magnitude of 4-10 as compared to that from unprocessed nanopillar sample. In addition, a PL peak energy redshift was observed after mass transport, presumably due to the decrease in the lateral barrier potential from vacuum to GaAs, as well as the elimination of the depletion layer. Furthermore, the mass transport process in the high vacuum MBE environment enables GaAs overgrowth with few defects and dislocations following mass transport for surface planarization. PL emission intensity increased by an additional factor of 4 following GaAs overgrowth, bringing the QD intensity to 1 2 of that of the original single quantum well. Thus, the potential of the MBE-assisted mass transport process has been demonstrated to fabricate high optical quality InGaAs quantum dots encapsulated in a GaAs matrix for device applications

Investigation of Plasmon Resonance Tunneling through Subwavelength Hole Arrays in Highly Doped Conductive ZnO Films

Experimental results pertaining to plasmon resonance tunneling through a highly conductive zinc oxide (ZnO) layer with subwavelength hole-arrays is investigated in the mid-infrared regime. Gallium-doped ZnO layers are pulsed-laser deposited on a silicon wafer. The ZnO has metallic optical properties with a bulk plasma frequency of 214 THz, which is equivalent to a free space wavelength of 1.4 μm. Hole arrays with different periods and hole shapes are fabricated via a standard photolithography process. Resonant mode tunneling characteristics are experimentally studied for different incident angles and compared with surface plasmontheoretical calculations and finite-difference time-domain simulations. Transmission peaks, higher than the baseline predicted by diffraction theory, are observed in each of the samples at wavelengths that correspond to the excitation of surface plasmon modes

Thick Hydride Vapor Phase Heteroepitaxy: A Novel Approach to Growth of Nonlinear Optical Materials

At the time when many nonlinear optical (NLO) materials for frequency conversion of laser sources in the mid and long-wave infrared have achieved their fundamental or technological limits, we propose heteroepitaxy as a solution to develop novel NLO materials. Heteroepitaxy, is the most applied method to combine two different materials—by growing one material on another. In this work we show that combining two binary materials in a ternary may significantly improve the NLO properties that are of great importance for the pursued applications. Plus, due to the closer lattice match to the related substrate, a ternary is always a more favorable heteroepitaxial case than the two completely different materials. We also discuss combining different growth methods—one close-to-equilibrium (e.g., hydride vapor phase epitaxy—HVPE) with one far-from-equilibrium (e.g., metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE)) growth processes—to explore new opportunities for the growth of novel heterostructures, including ternary layers with gradual change in composition. The combination of different materials by nature—organics with inorganics—in a hybrid quasi-phase matching (QPM) structure is another topic we briefly discuss, along with some innovative techniques for the fabrication of orientation-patterned (OP) templates, including such that are based on the most universal semiconductor material—Si. Still, the focus in this work is on a series of NLO materials—GaAs, GaP, ZnSe, GaSe, ZnTe, GaN… and some of their ternaries grown with high surface and crystalline quality on non-native substrates and on non-native OP templates using hydride vapor phase epitaxy (HVPE). The grown thick device quality QPM structures were used for further development of high power, compact, broadly tunable frequency conversion laser sources for the mid and longwave infrared with various applications in defense, security, industry, medicine and science

Conformal Spray-Deposited Fluorine-Doped Tin Oxide For Mid- And Long-Wave Infrared Plasmonics

Nanocrystalline spray-deposited fluorine-doped tin oxide (FTO) was investigated for mid- and long-wave infrared plasmonics. Silicon lamellar gratings were conformally coated with FTO, and the excitation of surface plasmon polaritons (SPP) was investigated via their angle and wavelength-dependent reflectivity. Photon-to-SPP coupling efficiency as a function of grating parameters, and in comparsion to gallium-doped zinc oxide (GZO) gratings, was quantitatively analyzed based on a figure of merit related to the sharpness and depth of the coupling resonance. Conformal spray-deposited FTO would be useful in mid- and long-wave infrared plasmonic channel wave guides

Long-Wavelength Infrared Surface Plasmons On Ga-Doped Zno Films Excited Via 2D Hole Arrays For Extraordinary Optical Transmission

Extraordinary optical transmission (EOT) through highly conductive ZnO films with sub-wavelength hole arrays is investigated in the long-wavelength infrared regime. EOT is facilitated by the excitation of surface plasmon polaritons (SPPs) and can be tuned utilizing the physical structure size such as period. Pulse laser deposited Ga-doped ZnO has been shown to have fluctuations in optical and electrical parameters based on fabrication techniques, providing a complimentary tuning means. The sub-wavelength 2D hole arrays are fabricated in the Ga-doped ZnO films via standard lithography and etching processes. Optical reflection measurements completed with a microscope coupled FTIR system contain absorption resonances that are in agreement with analytical theories for excitation of SPPs on 2D structures. EOT through Ga-doped ZnO is numerically demonstrated at wavelengths where SPPs are excited. This highly conductive ZnO EOT structure may prove useful in novel integrated components such as tunable biosensors or surface plasmon coupling mechanisms. © 2013 SPIE

Heteroepitaxial Growth Of Opgap On Opgaas For Frequency Conversion In The Ir And Thz

Abstract: For the first time thick orientation-patterned GaP (OPGaP) was repeatedly grown heteroepitaxially on OPGaAs templates as a quasi-phase matched medium for frequency conversion in the mid and longwave IR, and THz regions. The OP templates were fabricated by wafer-bonding and in a MBE-assisted polarity inversion process. Standard low-pressure hydride vapor phase epitaxy (LP-HVPE) was used for one-step growth of up to 400 μm thick device quality OPGaP with excellent domain fidelity. The presented results can be viewed as the missing link between a welldeveloped technique for preparation of OP templates, using one robust nonlinear optical material (GaAs), and the subsequent thick epitaxial growth on them of another material (GaP). The reason for these efforts is that the second material has some indisputable advantages in point of view of thermal and optical properties but the preparation of native templates encounters challenges, which makes it difficult to obtain high quality homoepitaxial growth at an affordable price. Successful heteroepitaxial growth at such a relatively high lattice mismatch (- 3.6%) in a close to equilibrium growth process such as HVPE is noteworthy, especially when previously reported attempts, for example, growth of OPZnSe on OPGaAs templates at about 10 times smaller lattice mismatch (+ 0.3%) have produced only limited results. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP, is a solution that will accelerate the development of high power, tunable laser sources for the IR and THz region, which are in great demand on the market

High Extinction Ratio Terahertz Wire-Grid Polarizers With Connecting Bridges on Quartz Substrates

A terahertz (THz) wire-grid polarizer with metallic bridges on a quartz substrate was simulated, fabricated, and tested. The device functions as a wide-band polarizer to incident THz radiation. In addition, the metallic bridges permit the device to function as a transparent electrode when a DC bias is applied to it. Three design variations of the polarizer with bridges and a polarizer without bridges were studied. Results show the devices with bridges have average s-polarization transmittance of less than -3 dB and average extinction ratios of approximately 40 dB across a frequency range of 220-990 GHz and thus are comparable to a polarizer without bridges