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We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal-organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the (¯201) orientation peaks of -Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 x1018 cm-3 and mobility of ~770 cm2V-1s-1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance-voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 x1013 cm-2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV-1. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices.

Epsilon-near-zero (ENZ) materials have been key players in recent photonic applications due to their versatility in growth, excellent compatibility, and ability to be dynamically modulated. From a foundation in the recently developed carrier kinetic models of nonlinearities in ENZ materials, we discuss our efforts to realize scalable and high-quality Al:ZnO (AZO) films via a unique atomic layer deposition (ALD) process, and the use of AZO in both switching and frequency shifting applications. Throughout, we highlight the advantages and challenges that exist and conclude with an outlook for ENZ materials in the area of nonlinear optics.

A mechanically robust metasurface exhibiting plasmonic colors across the visible and the near-IR spectrum is designed, fabricated, and characterized. Thin TiN layers (41 nm in thickness) prepared by plasma-enhanced atomic layer deposition (ALD) are patterned with sub-wavelength apertures (75 nm to 150 nm radii), arranged with hexagonal periodicity. These patterned films exhibit extraordinary transmission in the visible and the near-IR spectrum (550 nm to 1040 nm), which is accessible by conventional Si CCD detectors. The TiN structures are shown to withstand high levels of mechanical stresses, tested by rubbing the films against a lint-free cloth under 14.5 kPa of load for 30 minutes, while structures patterned on gold, a widely used plasmonic material, do not. The subwavelength nature of the plasmonic resonances, coupled with robustness and durability of TiN, makes these structures an attractive choice for use in nanoscale security features for heavily handled objects. Furthermore, ALD of these films enables scalability, which in conjunction with the cost-effectiveness of the process and material (TiN) makes the entire process industry friendly.

This article discusses challenges in designing optically transparent antennas and filters for smart city applications. The smart city concept seeks to alleviate urban challenges that include infrastructure and network capacity. The proposed frequencies for the next generation of wireless networks (5G) would result in shorter broadcast distances and network dead zones. Additional access points and signal repeaters embedded into the existing infrastructure, by inserting transparent antennas into windows via either meshed conductors or transparent conductive oxides (TCOs), would help to mitigate these issues. Glass-embedded frequency-selective surfaces (FSSs) can be used anywhere that requires microwave filtering and optical transparency. The cyberphysical system security in this forthcoming network also poses challenges to entities that require strict network security. This article focuses mainly on TCOs, particularly doped zinc oxide (ZnO), as promising material for transparent antennas and filters. To demonstrate the potential of ZnOs as highly transparent conductive materials for antenna and filter applications, we designed, fabricated, and tested a gallium-doped ZnO- (GZO) based optically transparent 2.4-GHz Wi-Fi antenna and two FSSs (bandpass and bandstop filters) operating in the 23-29-GHz frequency range. These results confirm the potential for ZnO-based TCOs as suitable alternatives to indium tin oxide (ITO) for microwave applications.

We report the direct current (DC) and microwave performance of BeMgZnO/ZnO heterostructure field effect transistors (HFETs) on sapphire substrates. The devices fabricated using Al2O3 as the gate dielectric with a gate length of 1.5 um and a gate width of 75 um exhibited a pinch-off voltage of −4.0 V and a maximum peak transconductance of 63 mS/mm. A current gain cutoff frequency fT of 5.0 GHz was achieved, highest among ZnO-based FETs. The corresponding electron velocity of above 1E7 cm/s estimated based on the gate transit time inches closer to the theoretical peak velocity in ZnO (3.5E7 cm/s). This value is significantly higher than the previously reported values in ZnO-based HFETs, which is attributed to the two-dimensional electron gas (2DEG) concentration at or near the resonance of longitudinal optical (LO)-phonon and plasmon frequencies as well as the improved quality of the heterostructure owing to optimized ZnO buffer growth and BeO and MgO alloying in the barrier. To probe the high-frequency response of the HFETs, extrinsic and intrinsic parameters of the small-signal equivalent circuit for the BeMgZnO/ZnO HFETs were investigated using the hybrid extraction method.

Recently, materials with vanishing refractive index, near-zero-index (NZI), have garnered considerable amount of attention, primarily for their ability to exhibit enhanced light matter interaction, due to slow light affects. Furthermore, effects such as static light, enhanced nonlinearities and emission tailoring have made such materials a heavily researched area. Amongst them, transparent conducting oxides (TCOs), a class of materials that have vanishing index at technologically relevant near-IR spectral range, are increasingly being investigated, for their potential use in photonic circuits. Wide natural abundance of ZnO together with well-studied properties make ZnO-based TCOs, such as aluminum- and gallium-doped ZnO particularly attractive for NZI applications.

We report a plasmon-driven thermomechanical switch, which is actuated using the ohmic losses of plasmons as a highly concentrated and thermally isolated heat source. This device operates with sub-15ns switching time and sub-10mW power consumption.

Plasmonic-based integrated nanophotonic modulators, despite their promising features, have one key limiting factor of large insertion loss (IL), which limits their practical potential. To combat this, we utilize a plasmon-assisted approach through the lens of surface-to-volume ratio to realize a 4-slot based EAM with an extinction ratio (ER) of 2.62 dB/µm and insertion loss (IL) of 0.3 dB/µm operating at ∼1 GHz and a single slot design with ER of 1.4 dB/µm and IL of 0.25 dB/µm operating at ∼20 GHz, achieved by replacing the traditional metal contact with heavily doped indium tin oxide (ITO). Furthermore, our analysis imposes realistic fabrication constraints, and material properties, and illustrates trade-offs in the performance that must be carefully optimized for a given scenario.

Data usage across the internet is growing exponentially, fueled primarily by the move to cloud computing and penetration of streaming services into developing countries. To address the growing energy needs of data centers, we propose an all oxide plasmon assisted electro-optic modulator, which features enhanced light-matter interaction, and compact sizes as seen in plasmonic modulators while at the same time maintaining low insertion losses, as seen in photonic modulators. This is achieved by utilizing a device design that selectively engages and disengages the lossy plasmonic component, as the device switches from low transmission to high transmission modes.

The subwavelength nature of the plasmonic resonances, observed in patterned thin metallic films, makes it an attractive choice for use in application such as security features, product branding and data storage and imaging. However, these have largely been limited by the practical issues of cost and robustness arising from the use of gold, silver or aluminum. Here we pattern TiN thin films, a well explored alternative plasmonic material, with sub wavelength apertures, arranged with hexagonal periodicity, which exhibit extraordinary transmission in the visible and near IR spectrum. These TiN structures are shown to withstand different levels of mechanical stresses, while gold doesn’t, making TiN an attractive platform for use as security features.

Implantable or subcutaneous biosensors used for continuous health monitoring have a limited functional lifetime which requires frequent replacement and therefore may be highly discomforting to the patient and become costly. One possible solution to this problem is the use of biosensor arrays where each individual reserve sensor can be activated on-demand when the previous one becomes inoperative due to biofouling or enzyme degradation. Each reserve biosensor in the array is housed in an individiual Polydimethylsiloxane (PDMS) well and is protected from exposure to bodily fluids such a s interstitial fluid (ISF) by a thin-film nitrocellulose me mbrane. Controlled activation is achieved by decomposing over an individual sensor well. Electrically activated decomposition of the nitrocellulose membrane is caused by passing an electric current through a Au/Ti filament placed on top of the membrane. By applyingan energy of 7 mJ to the Au/Ti filament with cross-sectional area of $8\times 10^{7}\mathrm{cm}^{2}$ , a current density of ≈ 10 5 –10 6 A/cm 2 causes explosive decomposition of thin-film Au. Having a thermal decomposition temperature of ≈ 200°C, nitrocellulose is locally heated directly under the Au/Ti filament. This leads to opening of the nitrocellulose membrane allowing for exposure of biosensor to the biofluid.

Previously we have conducted researches on the molecular beam epitaxy (MBE) of Zn-polar BeMgZnO/ZnO heterostructure field effect transistor (HFET) structures on GaN templates, which exhibit both high two-dimensional gas (2DEG) density and high electron mobility with relatively low Mg contents via the strain modulation of Be and Mg co-incorporation. In this contribution, we report on the growth of the HFET structures directly on sapphire substrate by employing a buffer consisting of a rock-salt structure MgO layer, a low-temperature (LT) ZnO layer and a high-temperature (HT) ZnO layer. Compared with growth of O-polar on sapphire, in which a thin and wurtzite MgO buffer is deposited at high temperatures above 700 °C, the MgO buffer for Zn-polar growth has to be reduced to 450 °C, in order to obtain smooth interface and surface for the BeMgZnO/ZnO HFETs. The residual electron sheet concentration in Zn-polar ZnO layers is ~2×1012 cm-2 on GaN while semi-insulating Zn-polar ZnO layers on sapphire have been obtained via controlling the buffer growth conditions, which is vital to the realization of HFET device structures.

Photoluminescence (PL) was used to estimate the concentration of carbon in GaN grown by hydride vapor phase epitaxy (HVPE). The PL data were compared with profiles of the impurities obtained from secondary ion mass spectrometry (SIMS) measurements. Comparison of PL and SIMS data has revealed that apparently high concentrations of C and O at depths up to 1 µm in SIMS profiles do not represent depth distributions of these species in the GaN matrix but are rather caused by post-growth surface contamination and knocking-in impurity species from the surface. In particular, PL analysis supplemented by reactive ion etching up to the depth of 400 nm indicates that the concentration of carbon in nitrogen sites is below 2–5 × 1015 cm−3 at any depth of GaN samples grown by HVPE. We demonstrate that PL is a very sensitive and reliable tool to determine the concentrations of impurities in the GaN matrix.

The Portable In Vitro Exposure Cassette (PIVEC) was developed for on-site air quality testing using lung cells. Here, we describe the incorporation of a sensor within the PIVEC for real time monitoring of cellular oxidative stress during exposure to contaminated air. An electrochemical, enzymatic biosensor based on cytochrome c (cyt c) was selected to measure reactive oxygen species (ROS), including hydrogen peroxide and super oxides, due to the stability of signal over time. Human A549 lung cells were grown at the air���liquid interface and exposed within the PIVEC to dry 40 nm copper nanoparticle aerosols for 10 minutes. The generation of ROS compounds was measured during exposure and post-exposure for one hour using the biosensor and compared to intracellular ROS determined using the 2���,7���-dichlorodihydrofluoroscein diacetate (DCFH-DA) assay. A similar increase in oxidative stress upon aerosol exposure was measured using both the cyt c biosensor and DCFH-DA assay. The incorporation of a biosensor within the PIVEC is a unique, first-of-its-kind system designed to monitor the real-time effect of aerosols.

This study evaluated the cytocompatibility of single- and poly-crystalline ZnO thin films using extract and direct contact methods. Exposure to poly-crystalline ZnO extract resulted in reduced cell viability, on average 82%/70% as measured by MTS/LDH assays, respectively. Direct exposure to both single- and poly-crystalline ZnO thin films resulted in reduced cell viability, which was attributed to anoikis due to inhibition of cell adhesion to the substrate by zinc. Intracellular zinc imaging suggests that single crystalline ZnO thin films do not result in a significant change in intracellular zinc concentrations. Overall, the results suggest that single-crystalline ZnO thin films have better short-term (24 h) cytocompatibility and support their potential to serve as a biocompatible sensor material.

Microwave noise is used to study high-electric-field electronic properties of ZnO channels with electron densities in the range from 1017 to 1019 cm–3. The strong source of noise is observed to superimpose onto the standard hot-electron noise governed by the hot-electron energy relaxation. At a given current, the excess noise temperature Δ T n increases with the channel length, and values up to and above 10 000 K are reached. The steep dependence Δ T n ∝ I 12 on the current I approximately holds for the longest channels. The source of noise in question is suppressed in ZnO epilayers at high electron densities and in a ZnO/MgZnO heterostructure with two-dimensional electron gas. The observed results are evaluated and discussed in terms of the self-formation of high field domains. The estimated domain voltage U d increases with the current; the dependence is close to U d ∝ I 6. The domain self-formation is additionally confirmed by measuring the spectral density of current fluctuations; the usual hot-electron noise turns into shot noise as the current increases. The Fano factor demonstrates an increasing number of nearly ballistic electrons that traverse the self-supporting domain.

Owing to its large bandgap covering the UV region of the optical spectrum, the quaternary BeMgZnO is of interest, particularly the collective effect Be and Mg fluxes on the solid composition. Incorporation of Be, Mg, and Zn in the wurtzite BeMgZnO quaternary alloy was found to depend strongly on the reactive-oxygen to metal flux ratio during growth by plasma-assisted molecular beam epitaxy under metal-rich conditions. For a given set of metal fluxes, reducing the VI/II (oxygen to metal flux) ratio from 1.0 to 0.6 increased the bandgap from 4.0 eV to 4.5 eV and decreased the c lattice parameter from 5.08 A to 5.02 A. The corresponding change in composition from Be 0.07 Mg 0.21 Zn 0.72 O to Be 0.10 Mg 0.34 Zn 0.56 O was consistent with a systematic reduction in the Zn incorporation coefficient from 0.23 to 0.12, while those of Be and Mg remained at ∼1. This behavior was explained by the substantially lower formation enthalpies of wurtzite BeO and MgO, −5.98 eV and −5.64 eV, respectively, compared to that of ZnO, −3.26 eV, determined using first principles calculations, as well as the high equilibrium vapor pressure of Zn, which results in re-evaporation of excessive Zn from the growing surface, details of which are the topic of this manuscript.

Accumulation of non-equilibrium hot longitudinal optical (LO) phonons limits the electron drift velocity for electronic devices operating under high electric field. Ultrafast decay of hot phonons can take place via plasmon-LO phonon resonance, which leads to fast electron energy relaxation and hence high electron drift velocity and optimum operation of the devices. This need motivates us to create heterostructures with 2DEG density close to the plasmon-LO phonon resonance region. Through incorporating a few percent of Be into the BeMgZnO barrier to switch the strain sign in the barrier from compressive to tensile, we have achieved 2DEG densities over a wide range in Zn-polar BeMgZnO/ZnO heterostructures with moderate Mg content (below 30%) grown by molecular beam epitaxy. We have obtained electron mobility of 250 cm2/Vs at room temperature (293 K) and 1800 cm2/Vs at 13 K in Be0.02Mg0.26ZnO/ZnO heterostructures. Via capacitance-voltage (CV) spectroscopy, we have explored the depth profiles of the apparent carrier density of samples grown under different conditions. The correlations between electrical properties and MBE growth parameters of Zn-polar BeMgZnO/ZnO heterostructures are discussed.

Patterned titanium nitride films grown via PE-ALD exhibit plasmonic colors along with being scratch resistant and durable making them an attractive choice for applications that require robust materials such as security holograms and labels.

We demonstrate high plasmonic quality TiN on Si (001) via PE-ALD. Employment of an MgO buffer improved the figure of merit (FoM) at 1550 nm from 2.0 to 2.5 and the peak FoM from 2.4 to 2.8.

Titanium nitride (TiN) is highly attractive for plasmonics and nanophotonics applications owing to its gold‐like but tunable optical properties. Its prodigious potential for plasmonics has been demonstrated on sapphire or bulk MgO. For a transformational impact, high optical quality TiN on Si is required instead, which would support the integration of nanophotonics with the complementary metal‐oxide‐semiconductor (CMOS) electronics. However, TiN grown on Si, even at elevated temperatures, lacks the optical quality needed, imposed by the large lattice mismatch between them. Here, a novel approach is reported wherein a thin MgO interlayer is inserted between TiN and Si. The improved crystalline quality enabled by MgO for TiN on Si(001) leads to a significant enhancement of the plasmonic figure of merit (FOM = −ε′/ε″) from 2.0 to 2.5 at telecommunication wavelength (peak FOM of 2.8), which is comparable to the widely accepted ultimate FOM obtained on bulk MgO grown under similar conditions. The TiN/MgO/Si structure enables the hybrid‐plasmonic‐photonic waveguide platform with sufficiently low losses, and thus long propagation lengths, for nanophotonic devices while providing additional practical advantages such as serving as a self‐aligned robust etching mask. Thus, the much‐anticipated potential of TiN on Si platform for CMOS compatible plasmonics is brought closer to reality.

Typical guided-mode resonance (GMR) transmission filter design, which is based on a single ridge per period, necessitates multiple etching/fabrication steps for implementing an array of filters (having different transmission bands) on the same substrate. To address this problem, we demonstrate dual-period narrow bandpass GMR filters that offer more degrees of freedom, two periods and two fill-factors, for tuning the filter characteristics and achieving wider stop bands without changing the grating height. A set of six transmission filters with well-separated passbands in the short-wave infrared region was designed using COMSOL Multiphysics simulations and produced on the same silicon-on-quartz wafer in a single fabrication run. The 90 µ m × 90 µ m size filters exhibited passbands as narrow as 15 nm with peak-wavelength tunability over 200 nm, flat stop bands as wide as ∼ 400 n m , and peak transmittance reaching 87%. The experimental transmission spectra were in good agreement with the corresponding simulations. These findings pave the way for the realization of pixel size filter arrays for multispectral image sensors.

Major technological breakthroughs are often driven by advancements in materials research, and optics is no different. Over the last few years, near-zero-index (NZI) materials have triggered significant interest owing to their exceptional tunability of optical properties and enhanced light-matter interaction, leading to several demonstrations of compact, energy-efficient, and dynamic nanophotonic devices. Many of these devices have relied on transparent conducting oxides (TCOs) as a dynamic layer, as these materials exhibit a near-zero-index at telecommunication wavelengths. Among a wide range of techniques employed for the deposition of TCOs, atomic layer deposition (ALD) offers advantages such as conformality, scalability, and low substrate temperature. However, the ALD process often results in films with poor optical quality, due to low doping efficiencies at high (>1020cm−3) doping levels. In this work, we demonstrate a modified ALD process to deposit TCOs, taking Al:ZnO as an example, which results in an increase in doping efficiency from 13% to 54%. Moving away from surface saturation for the dopant (aluminum) precursor, the modified ALD process results in a more uniform distribution of dopants (Al) throughout the film, yielding highly conductive (2.8×10−4 Ω-cm) AZO films with crossover wavelengths as low as 1320nm and 1370nm on sapphire and silicon substrates, respectively.

The almost periodic streaming motion of accelerated electrons under moderate electric fields coupled with almost periodic emission of longitudinal optical (LO) phonons is studied in a gallium nitride quantum-well—a promising pathway for terahertz (THz) oscillations. The optimal conditions for the LO-phonon-terminated streaming depend, among others, on the density of the electron gas, the low-field electron mobility, the lattice temperature, and the electric field in a very specific way. The present manuscript exploited the electron noise temperature measured at an X band frequency as a marker for the oscillations at THz frequencies. The idea was tested on a deterministic model for a GaN two-dimensional electron gas (2DEG) through calculation of the electron noise temperature spectra in the Langevin approach for the frequency range from 1 GHz to 10 THz. The noise temperature at 10 GHz was found to be in a strong anticorrelation with the THz peaks in the noise temperature spectrum. In particular, a weaker dependence on the applied electric field at 10 GHz implies stronger THz oscillations. In an experiment, the microwave hot-electron noise measurements were carried out for AlGaN/AlN/GaN heterostructures with the 2DEG channel at 10 GHz under pulsed electric field conditions in order to mitigate the effect of Joule heating of the channel. The plateau-like behavior of the noise temperature, in its dependence on the electric field, was obtained for the 2DEG channels with rather low electron densities ( 2.5 × 10 12 cm − 2) in a good agreement with the model. The aforementioned plateau in the electron noise temperature observed at 10 GHz can be used as an indicator for the THz oscillations.

To integrate plasmonic devices into industry, it is essential to develop scalable and CMOS compatible plasmonic materials. In this work, we report high plasmonic quality titanium nitride (TiN) on c-plane sapphire grown by plasma-enhanced atomic layer deposition. TiN with low losses, high metallicity, and a plasma frequency below 500 nm was achieved at temperatures less than 500 °C by exploring the effects of chemisorption time, substrate temperature, and plasma exposure time on the material properties. A reduction in chemisorption time mitigates premature precursor decomposition at TS > 375 °C, and a trade-off between reduced impurity concentration and structural degradation caused by plasma bombardment is achieved for 25 s plasma exposure. 85 nm thick TiN films grown at a substrate temperature of 450 °C, compatible with CMOS processes, with 0.5 s chemisorption time and 25 s plasma exposure exhibited a high plasmonic figure of merit ( | e ′ / e ′ ′ |) of 2.8 and resistivity of 31 μ Ω cm. As a result of the improved quality, subwavelength apertures were fabricated in the TiN thin films and are shown to exhibit extraordinary transmission.

Growth of ZnO directly on c-plane sapphire, with a large in-plane lattice mismatch of 18%, is relatively well understood for O-polar variety. However, the two-dimensional (2D) growth of Zn-polar ZnO on c-sapphire, needed for 2D electron gas formation, with low background electron density is in its infancy. While Zn-polar ZnO can be grown on GaN with the resulting small lattice mismatch (1.8%), the parallel conduction through GaN (bulk and/or surface) in fabricated BeMgZnO/ZnO heterostructure field effect transistors (HFETs) limits its utility for the time being. In this contribution, the authors report on the growth of high-quality Zn-polar BeMgZnO/ZnO HFET structures directly on sapphire substrates, in an effort to avoid the aforementioned parallel conduction, by employing an MgO and low-temperature ZnO buffer stack. The residual 2D equivalent concentration in the HFET structure on GaN is ∼2 × 1012 cm−2, which is detrimental, while highly resistive (>100 Ω.cm) Zn-polar ZnO layers with smooth surfaces on c-sapphire have been obtained via controlling the buffer stack growth conditions, which is vital to the realization of HFET device structures. Compared with the highest room temperature electron mobility of ∼250 cm2/V s in BeMgZnO/ZnO HFETs on GaN templates, a slightly lower electron mobility of ∼220 cm2/V s was achieved on c-sapphire due to a somewhat lower overall crystalline quality.

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

International audience; In semiconductor heterojunction, polarity critically governs the physical properties, with an impact on electronic or optoelectronic devices through the presence of pyroelectric and piezoelectric fields at the active heteropolar interface. In the present work, the abrupt O-polar ZnO/Ga-polar GaN heterointerface was successfully achieved by using high O/Zn ratio flux during the ZnO nucleation growth. Atomic-resolution high-angle annular dark-field and bright-field transmission electron microscopy observation revealed that this polarity inversion confines within one monolayer by forming the (0001) plane inversion domain boundary (IDB) at the ZnO/GaN heterointerface. Through theoretical calculation and topology analysis, the geometry of this IDB was determined to possess an octahedral Ga atomic layer in the interface, with one O/N layer symmetrically bonded at the tetrahedral site. The computed electronic structure of all considered IDBs revealed a metallic character at the heterointerface. More interestingly, the presence of two-dimensional (2D) hole gas (2DHG) or 2D electron gas (2DEG) is uncovered by investigating the chemical bonding and charge transfer at the heterointerface. This work not only clarifies the polarity control and interfacial configuration of the O-polar ZnO/Ga-polar GaN heterojunction but, more importantly, also gives insight into their further application on heterojunction field-effect transistors as well as hybrid ZnO/GaN optoelectronic devices. Moreover, such polarity control at the monolayer scale might have practical implications for heterojunction devices based on other polar semiconductors.

This contribution presents the design and simulation of finite size narrow band transmission filters for applications in realtime and remote short wave infrared (SWIR) spectroscopy and imaging. The results can ultimately be extended to hyperspectral imaging that has gained interest in many fields ranging from agriculture to surveillance. As chemical compounds possess unique set of sharp spectral signatures, they can be differentiated using wideband spectral scanning. However, such standard approaches require bulky instruments and long acquisition times together with post-processing of acquired data. These technological bottlenecks result in a diminished usefulness of such systems in scenarios demanding short response times, such as law enforcement, homeland security, and military applications. To overcome these limitations, narrow-band and pixel-size filters can be incorporated to focal plane arrays for real-time spectral imaging systems. In this study, we explored several designs of narrow-band, finite-sized (

This study evaluated the cytocompatibility of single- and poly-crystalline ZnO thin films using extract and direct contact methods. Exposure to poly-crystalline ZnO extract resulted in reduced cell viability, on average 82%/70% as measured by MTS/LDH assays, respectively. Direct exposure to both single- and poly-crystalline ZnO thin films resulted in reduced cell viability, which was attributed to anoikis due to inhibition of cell adhesion to the substrate by zinc. Intracellular zinc imaging suggests that single crystalline ZnO thin films do not result in a significant change in intracellular zinc concentrations. Overall, the results suggest that single-crystalline ZnO thin films have better short-term (24 h) cytocompatibility and support their potential to serve as a biocompatible sensor material.

We investigate and find that the quality of titanium nitride grown at 350°C and 375°C using atomic layer deposition on silicon and sapphire substrates respectively are approaching the metallicity of sputtered films.

Owing to its suitable material properties, such as large direct bandgap (3.37 eV) and large exciton binding energy (60 meV) and ease of production compared to other compound semiconductors, ZnO has been at the focus of momentous interest for potential applications in optical devices, transparent ohmic contacts, transparent thin film and heterostructure transistors, chemical/bio sensors, and piezotransducers. However, lack of reproducible and sufficient p-type conductivity in ZnO has so far prevented its introduction to the commercial light emitter applications. Like other semiconductor systems, advanced deposition methods such as molecular beam epitaxy (MBE) has allowed invaluable insight into the growth dynamics and fundamental properties of ZnO thanks to its fine control over growth parameters. This chapter discusses MBE growth of ZnO and related materials and the progress in the development of high-quality epitaxial layers and ZnO-based devices after reviewing the growth-related material properties such as crystal structure, lattice parameters, and thermal properties. In addition to bandgap engineering, doping and heterostructure devices, mainly optical emitters and transistors based on ZnO, are discussed. It has been shown that ZnO could address niche applications such as transparent contacts and thin film transistors and polariton lasers. Moreover, further improvements in p-type conductivity in ZnO by codoping using MBE might pave the way for high-efficiency ZnO light emitting devices.

We investigate the quality of atomic layer deposited Titanium nitride thin films and find metallicity close to high quality sputtered films on both sapphire and silicon for a deposition temperature of 375°C.