Positron annihilation spectroscopy has been applied to study the vacancy-type defects in a wide range of β-Ga₂O₃ bulk crystals and thin films. The experimental data show that all studied samples contain high concentrations of Ga vacancies in a split vacancy configuration. These split Ga vacancies are observed also with other experimental techniques, and theoretical calculations predict that their formation energies are lower than those of other vacancy configurations. The exact structure of the split Ga vacancies appears to vary across samples.

The interaction of transparent oxide semiconductors with light is critically important for a range of applications. Persistent effects could be exploited for holographic memory or optically defined circuits. Conversely, they may also be detrimental to device operation. Large, room-temperature persistent photoconductivity (PPC) was discovered in strontium titanate (SrTiO₃, STO) after annealing in a hydrogen-containing atmosphere. Barium titanate (BaTiO₃, BTO), a ferroelectric material, was recently found to also exhibit PPC. Room-temperature photodarkening was observed in Cu-doped gallium oxide (β-Ga₂O₃) after exposure to sub-bandgap light. Hydrogen is believed to play a central role in these persistent phenomena. In the proposed model, a photon excites substitutional hydrogen (a proton inside an oxygen vacancy), making the defect unstable. The proton leaves and binds to a host oxygen atom, forming an O-H bond that is observed with infrared spectroscopy. An oxygen vacancy is left behind. Because oxygen vacancies in STO and BTO are shallow donors, this process results in PPC. In β-Ga₂O₃:Cu, however, the oxygen vacancy neighbors a Cu acceptor. In that case, photoexcitation results in the rare Cu³⁺ state, which absorbs visible light. The effect can be “erased” by annealing at 300-400°C.

Gate leakage currents present a serious challenge for designing modern ultra-scaled metal-oxide-semiconductor (MOS) field effect transistors. While trap-assisted tunneling (TAT) has already been recognized as a major contribution to leakage currents in nanoelectronic devices, the microscopic nature of the traps acting as charge transition centers is still unclear. In this work we utilize a multi-scale modeling approach to link TAT to polaron states, which are acting similar to traps and are intrinsic to the amorphous gate dielectric. We first use density functional theory to study the electronic structure and the charge trapping dynamics of such polarons on an atomistic level in common gate dielectrics like SiO₂ or ZrO₂. From those calculations a nonradiative multiphonon model is derived to describe the charge hopping process between nearby polarons. Finally, the macroscopic gate leakage current is obtained from a Monte-Carlo device simulation, taking into account the stochastic distribution of trapping sites and their varying parameters due to the amorphous host material. By comparing the results of our simulation framework to experimental investigations on gate leakage currents for SiC/SiO2 and TiN/ZrO2 MOSCAPs, we provide compelling evidence that polarons are very likely the root cause for leakage currents in the studied devices. Our simulations further suggest that general features of these polarons, like the comparatively small relaxation energy, make them a universal source for steady-state leakage currents beyond the particular materials studied in this work.

We demonstrated a metal-organic chemical vapor deposition (MOCVD) of smooth and thick monoclinic phase-pure gallium oxide (Ga₂O₃) on c-plane sapphires using silicon-oxygen bonding (SiO_x) as a phase stabilizer. We were able to grow ~580nm thick β-Ga2O3 on sapphire by MOCVD at 700 oC through phase stabilization using silane. The samples grown with silane show a reduction in the surface roughness and resistivity from 10 nm to 5 nm and from 371 Ω.cm to 136 Ω.cm, respectively. X-ray diffraction (XRD) reveals a pure-monoclinic phase. Our findings indicate that a thick, phase-pure β-Ga2O3 can be grown on c-plane sapphire, which can lead to its growth on thermally conducting substrates which is critical for creating power devices with better thermal management.

Properties of monoclinic β-Ga2O3 are strongly dependent upon orientation. In the case of optical properties, polarization can reveal differences in optical bandgap and absorptions related to transition metal ions. This phenomenon is known as pleochroism and has been extensively studied in minerology. β-Ga2O3 bulk single crystals doped with Zn, Mn, Cr, or Cu were grown by the Czochralski and vertical gradient freeze methods. Ultraviolet-visible-near infrared spectroscopy and photoluminescence (PL) revealed polarization- and orientation-dependent optical absorptions in β-Ga2O3. Crystals were annealed in reducing and oxidizing environments in an attempt to alter the intensities of absorptions characteristic to the different transition metal oxidation states in a given ligand field. Visible pleochroism was strongest in (001) oriented Mndoped samples as shown by polarized optical microscopy. All samples were electrically insulating, indicative of acceptor doping, aside from Cr-doped samples where Cr acts as a deep donor.

We discuss the potential of heterogenous integration of Ga₂O₃ with diamond for enabling energy-efficient kV-class power devices. The integration alleviates Ga₂O₃ material drawbacks such as its low thermal conductivity and inefficient hole conductivity. The benefits of heterogeneous integration are demonstrated through electrical and thermal simulations of a Ga₂O₃-Al₂O₃-diamond superjunction based Schottky barrier diode. The simulation studies show that the novel device has potential to break the RON-breakdown voltage limit of Ga₂O₃, while showing relatively low rise in temperature compared to conventional devices. First steps for the actual materials integration are taken with the epitaxial growth of Ga₂O₃ on single crystal diamond substrates.

There is a surge in interest for the ultra wide bandgap (Eg ~ 4.9 eV) semiconductor gallium oxide (Ga₂O₃). A key driver for this boom is that single crystal wide area bulk β-Ga₂O₃ substrates have become commercially available and that a variety of methods have been shown to give high quality epitaxial growth. Amongst a whole range of potential applications (power/switching electronics, solar transparent electrodes, etc.) extreme solar blindness photodetectors in β- Ga₂O₃, the more stable monoclinic phase of Ga₂O₃, offers the most exciting perspectives for deep ultraviolet observations below 250 nm. We present an overview of the complete realization process (epitaxy, photolithography, singulation and packaging), and space qualification (to TRL8) of a series of β-Ga2O3 photodetectors We insist on their remarkable solar blindness performance (factor 1000 or more between peak responsivity around 215-220 nm and 250 nm) and dynamical properties (rise and fall times < 5 ms), along with their enhanced responsivity, excellent thermal behaviour and radiation hard properties. 4 of these detectors have been integrated on the INSPIRE-SAT 7 nanosatellite expected to be launched in April 2023 to reach the TRL9 "demonstrated in flight" qualification.

Tailoring the surface work function and/or surface functional group of oxide active layers in an optoelectronic device is an important means for performance improvement. One way to proceed is to adsorb molecules with varying dipole moment strength and sign. We report on the surface modification of mesoporous TiO₂ using different self-assembled monolayers (SAMs) of acids. The energetics at the interface have been determined using a series of photoelectron spectroscopy techniques (UPS, IPES, XPS). We have shown that the observed changes in work function is correlated to the dipole moments of the respective acids, calculated by density functional theory. This interfacial engineering approach can be used to control the charge extraction from an optoelectronic device. A novel approach is proposed for boosting the performances of self-powered photodetectors. Visible-blind UVA photodetectors have been built by combining a mesoporous TiO₂ layer with a Spiro-OMeTAD layer. SAMs interlayer induces a step in the vacuum energy, the formed dipole field dramatically affects the charge transfer and then the photocurrent/photoresponse of the device. The effect of para-substituted benzoic acids and β-alanine on the functioning of triple cation perovskite solar cells is then developed. We show then a best improvement for 4-chlorobenzoic acid SAMs which is due to the reduction of interfacial states, to the improvement of the quality of the perovskite material and to a better structural continuity.

Obtaining p-type wide bandgap semiconductors operating in the deep UV (DUV) range (λ < 300 nm) is still challenging. However, as a part of this work, we developed novel p-type solution-processed wide bandgap semiconductors based on solution-processed manganese oxide quantum dots (MnO-QDs) with the gap energy exceeding 4 eV synthesized by ultrafast laser ablation, which can be adopted for flexible and solar-blind DUV optoelectronics. We conducted advanced optical, structural, and electrical characterizations, revealing unique properties of this material. Our findings show excellent band alignment between these QDs and other wide bandgap semiconductors, such as GaN and Ga2O3. The high performance of a solar-blind self-powered DUV photodetector based on p−n junction that comprises n-type wide bandgap semiconductors and p-type MnO-QDs is demonstrated.

Ultraviolet (UV) photodetectors have gained vast technological interest over the past few years due to its wide band of applications in the emerging areas of intersatellite communications, astronomical studies, and biological applications. The present challenge in UV-detector development is to improve its photosensitivity, selectivity and response time with low power consumption, which create motivation to design and fabricate the self-powered heterojunctions devices. In this work, n­type Er-doped ZnO nanowires are grown on p-type Si to make a heterojunction device by using double-step chemical bath deposition (CBD) process. The crystalline nature, morphology, optical parameters are studied in detail by using SEM, XRD, CL and UV-Vis, respectively. The XRD results confirm the growth of vertical nanowires with (002) dominant planes and such peak shifts with the increasing Er-doping, which indicates the structural modifications and strain generation due to the substitutions of Er in ZnO lattice. The optical bandgaps of the Er-doped and undoped ZnO nanowires are estimated from UV-Vis absorbance, and corresponding change in optical properties with increasing doping concentrations are studied in detail. Room temperature CL spectra confirms the reduction of oxygen vacancy related surface defects in the nanowires with increasing Er doping concentrations due to the higher bond-dissociation energy between Er-O than Zn-O. The electrical properties of the undoped and Er-doped ZnO nanowires/Si heterojunctions are investigated by measuring I-V and such results exhibit superior heterojunction properties in terms of rectification ratio, ideality factor and barrier height. Finally, selective Er-doped ZnO nanowires heterojunction shows best self-powered photoresponse under relatively low power UV illumination and such improvement in responsivity, photo-to-dark current ratio and response speed of heterojunctions is attributed to the reduction of oxygen vacancy related defects due to Er-incorporation. Therefore, current work provides an insight into the development of self-powered UV detectors by employing a cost-effective doing technique.

In persistent luminescence materials, energy can be stored by controlled traps/defects under brief irradiation, namely few minutes under various wavelengths ranging from X-rays to natural daylight. This energy is then released at room temperature for several hours via light emission once the excitation is stopped. The paper is focused on the analysis of the persistent luminescence properties on single crystals of Ce³⁺ and Cr³⁺ co-doped gadolinium-yttrium-aluminum-gallium garnets of general formula Y_3-xGd_xAl₂Ga₃O₁₂ (YGAGG), to promote new applications of the persistent materials. Extending the range of excitation by using X-rays excitation is also proposed.

β-Ga₂O₃ is a wide bandgap semiconductor that is attractive for various applications, including power electronics, transparent conductive electrodes, etc. Electrical and optical properties of Ga₂O₃ are affected by the presence of dopants/contaminants and/or intrinsic defects. Here, we investigate the electrical and optical properties of transition metals like Co and Cr since they are often unintentionally present during the growth or used as intentional dopants. This is done by using magnetic resonance spectroscopy and magneto-optical characterization techniques. We determine spin- Hamiltonian parameters of the Cr³⁺ ground-state and first excited-state as well as the spin-Hamiltonian parameters of Co²⁺.

Prism-based surface plasmon resonance (SPR) optical sensors are extensively used in a variety of applications. In implementing a multilayer sensing structure, SPR phenomena are employed to detect gases in the proposed research. A BK7 glass prism is used as a sensing structure with decomposition on nano thin films based on different materials: silver (Ag), titanium dioxide (TiO2), and graphene. The methane gas is applied to the graphene sensing layer of the multilayer optical sensor. As the methane gas concentration rises around the sensor, the SPR angle varies, indicating that the refractive index of graphene layer is changed significantly due to absorption of the increasing methane gas concentration. The methane gas concentration measurement is based on an angle interrogation technique. TiO2, graphene, and Ag layers of different thicknesses have been optimised for sensor performance.

This experimental work presented the reduced graphene oxide (rGO) immobilized etched fiber Bragg grating (eFBG) sensor to improve refractometric sensitivity. The effectiveness of the proposed sensor is evaluated with cigarette smoke as well as incense smoke by monitoring the shift in the resonant peak of the reflection spectra of the sensor with the interrogator. An increase in the interaction of the evanescent field adsorbing with the smoke caused by the rGO layer increases the sensing performance. Raman spectroscopy, XRD, and field emission scanning electron microscope are used for characterization of the sensor.

High-temperature, chemically harsh processes underpin a wide range of applications ranging from power generation, infrastructure monitoring, chemical manufacturing, and many others. For such processes, in situ sensor data is a valuable tool for both optimization and safety, however, traditional sensor platforms can be limited in terms of stability at high temperatures or under highly corrosive, reducing, or oxidizing chemical conditions. Optical fiber-based sensing offers a unique tool for this type of harsh environment sensing application. Off-the-shelf silica fiber itself is highly stable up to ~800 °C, under a wide range of chemical conditions; while single crystal optical fiber expands this operational range even further, to temperatures well above 1000 °C. Work will be presented on the utilization of n-type semiconducting oxide thin films on single crystal sapphire fiber for the evanescent field-based sensing of reducing gas streams at temperatures up to 900 °C. The role of oxygen defects on the electrical and optical properties of the relevant films will be discussed, providing a theoretical background for the observed sensing response, time-dependence, and stability. Doped SrTiO3 systems (La_xSr_1-xTiO₃) will be discussed for hydrogen sensing at high temperatures. Strategies and challenges associated with pushing sensor and single crystal fiber performance above 1000 °C will also be discussed.

As an emerging energy conversion technology, electrochromism has attracted immense interest due to its various applications including variable optical filters, bistable displays and energy-efficient smart windows. Although the current electrochromic devices do not consume energy while maintaining their colored or colorless states, their bistable operation requires external electrical energy to be consumed during switching. As such, a novel design of Zn anodebased electrochromic devices was recently developed as a key strategy to partially retrieve the consumed electrical energy. Compared to conventional electrochromic devices, Zn anode-based electrochromic devices exhibit a rapid spontaneous switching behavior due to the high value of redox potential difference between a metal anode and an electrochromic cathode, thus providing the most energy-efficient consumption during operation. Moreover, Zn-based electrochromic devices enable independent operation of top and bottom electrochromic electrodes, thus providing additional configuration flexibility of the devices through the utilization of dual electrochromic layers under the same or different color states. As such, the color overlay effect can greatly broaden the color palettes via altering the coordinate of the 2D CIE color space. These key issues of Zn anode-based electrochromic devices make them very promising for the future development of electrochromic devices.

Giant room temperature persistent photoconductivity in hexagonal boron nitride under UVC irradiation has been demonstrated. Scanning lasers dots on sample surface at two different wavelengths (213 and 266 nm) have been used to induce such effect, the former being more efficient. Conductivity has been increased by 6 orders of magnitude upon illumination. Such increase persists significantly for at least 6 months. Decrease of photoinduced current has been shown to be 10% more important for samples irradiated under vacuum than for those irradiated under atmospheric pressure. Type of photoinduced carriers were investigated using p-hBN/n-AlGaN junctions through C/V measurements. P-type carriers are believed to be generated by 213 nm illumination whereas 266 nm laser is supposed to trigger n-type carriers.

We present a novel ultra-wide bandgap alloy system based on rutile-structured oxides (SnO₂-GeO₂-SiO₂), and clearly show their superior points from a point of view of both experiments and first-principles calculations. Experimentally, we demonstrate that mist-CVD method is effective for the fabrication of r-Ge_xSn_1−xO₂ alloy films. The r-Ge_xSn_1−xO₂ alloy films (x≤0.96) are composed of single-crystalline compounds, while phase separation is found in the r-GeO₂ films. The lattice parameters of r-GexSn1−xO2 alloy films decrease with an increase in fraction of Ge. Additionally, the bandgaps increase as the fraction of Ge increases. The compositional dependence of lattice parameters and bandgaps determined experimentally for the r-Ge_xSn_1−xO₂ alloy films is in good agreement with those derived by the calculations. Our measurements of electrical properties indicate that the r-Ge_xSn_1−xO₂ (x≤0.57) films are n-type semiconductors. Finally, we suggest band alignments calculated for r-Ge_xSn_1−xO2 and r-GexSi_1−xO₂ alloys. The results suggest a possibility of p-type doping in r-GeO2 and highly Ge-rich r-GexSn_1−xO₂. It is also suggested that it is preferable to use r-SiO₂ and highly Si-rich r-Ge_xSi_1−xO₂ as a blocking layer for other rutile-structured devices.

The silicon suboxide SiOx (x<2.0) offers promising application possibilities ranging from electrodes in lithium-ion batteries used widely in electrical vehicles and portable devices to sensing applications. Therefore, a low cost, environmental friendly and high performance oxide materials are required for an appropriate operation of any electronic gadget. In this work, we report on the physical and electrical properties of a suboxide formed as a seed layer during the formation of a dielectric layer, namely the ammonium silicon hexafluoride. The measurement results reveal interesting properties, which are required to be understood clearly before any application. The results have been analyzed using state-of-the-art techniques and compared with the developments of SiOx obtained by related techniques. In this presentation, a comprehensive review of the physical and electrical properties is given in order to clarify the origin of the observed features. At the end of the paper, a lookout is provided for the possible applications of this special SiOx dielectric seed layer.

This is a study of the potential of IBS for the production of high-quality ITO layers for optical applications with additional electrical requirements. The electrical properties of ITO layers combined with underlying optical interference layers and their optical properties and surface roughness are presented.

Process improvement for the manufacture of effective high performance gallium oxide (Ga2O3) based semiconductor devices is imperative in consolidating Ga2O3 as a singularly promising material for cost effective, mass-producible, and robust manufacturing. Other wide bandgap silicon alternatives (i.e., SiC and GaN) are impeded by high costs and complicated, time-consuming adjustments. Beginning with a bandgap of 4.7eV, Ga2O3 offers an unparalleled solution when growth parameters are tuned and controlled using deep reinforcement learning agents. Ga2O3 wafer production employs (non-exclusively) the scalable and cost-effective Czochralski method for ingot growth and MOCVD process for epitaxy growth, making it a viable candidate for high volume commercial radiofrequency device manufacture. As crystal quality and electron transport depend on reactor temperature, vertical gas and precursors flows, chamber pressure, and a host of kinetic parameters during growth, it follows that the configuration space for Ga2O3 deposition is expansive and costly to explore. Enhancing growth rate of Ga2O3 films without compromising crystal quality can be accomplished through implementing insights offered by ancillary deep learning models. Artificial intelligence techniques that take programmed reactor settings, sensor-read environmental conditions, resulting crystallographic defectivity, and overall outgoing quality as inputs can infer processing improvements upstream using neural networks trained by skilled engineers. My stipulations call for a hardware accelerated deep learning controller (DLC) that digests the multimedia output of reactors, MOCVD systems, and metrology tools to optimize Ga2O3 crystal quality and ultimately increase die yields, reduce waste, accelerate product development, decrease time to market, and eliminate need for labor-exhaustive testing.

Perovskite materials, despite displaying remarkable properties, suffer from the use of toxic lead and poor stability towards moisture and thermal stresses. These strongly hinder their future development. Recently, a new family of 3D perovskites, deficient in lead and iodide, the d-HPs, has been discovered. They involve large organic cations that circumvent the Goldschmidt tolerance factor. In the present study, we report that a new cation, the iodoethylammonium I-(CH₂)₂-NH₃⁺ (IEA⁺), allows the synthesis of d-HP thin films based on the 3D MAPbI₃ perovskite. This new compound has been tested for solar cell application. A final power conversion efficiency of 9.54 % was achieved.

The potential utility of two-dimensional transition-metal dichalcogenides (TMDs) in electronics, thermoelectrics, and spintronics have sparked an increase in scientific interest in the same. In accordance with this, we have done a study on VS₂ based device, using first principle Density Functional Theory (DFT) calculations combined with Non-equilibrium Green’s Function (NEGF) formalism to investigate spin transport properties. We constructed a toy-model of a 2-terminal VS₂ based device using MATLAB, and further applied a tunneling potential barrier across the channel and measured current through the same, on applying voltage across the terminals. Using the data obtained, we analyzed the spin filtering effect in the device by considering spin splitting in presence of magnetic field, and plotting the spin polarization (SP) and the magnetoresistance (MR) against bias voltage, respectively. The SP is observed to be 36% for a ballistic device between a bias range of 0.3 and 0.5V, which increases to 63% on applying a potential barrier of height twice the Fermi level of VS₂. For a ballistic device, we observed an increase in MR from 60% to 76% for large barrier height, within the same bias range as earlier. In each case, the peak value of current per unit cross sectional area of the device was found to be of the order of 10A/μm². Using these findings, we can conclude that our modeled VS₂ device exhibits properties to be used as a promising candidate for spintronic applications.

Charging persistent luminescence materials using an infrared laser as a power source and an upconversion process allows expanding the potential applications for these materials. In bioimaging at the nanoscale, it allows increasing recharge ability capacity, as the excitation wavelength is fully inside the biological window. In this work, we propose a novel approach to this phenomenon using energy transfer on associated materials. For this purpose, we have synthesized β- NaGd_0.8Y_0.17Er_0.03F₄ nanoparticles, known for their efficient upconversion, and Zn_1.33Ga_1.335Sn_0.33Cr_0.005O₄ nanoparticles known for their persistent luminescence properties, and we have associated them through a dry impregnation method. The obtained hybrid material presents persistent luminescence after charging with a 980 nm laser. A mechanism is proposed to explain the energy transfer process.

Hydrogen is considered fuel for the future, but its properties make it dangerous to use without protection from leaks and explosions, meaning that hydrogen gas sensors are necessary for safe use and storage of this important gas. Gas sensors based on semiconducting material like ZnO have been studied intensively, especially multiple methods of improving their parameters with doping, functionalization, etc. In this work, ZnO was doped with Eu during electrodeposition (ranging from 2 μM to 22 μM) and functionalized with Pd nanoparticles on its surface. The effects of doping and functionalization were studied, observing an improvement in response value (S) to 100 ppm hydrogen gas up to S~3965 at 150 °C of Pdfunctionalized ZnO:Eu nanosensor compared to S~150-200 to non-functionalized ZnO:Eu with similar doping concentration. The obtained results on a single Pd-functionalized ZnO:Eu nanowire-based nanosensor can be used for further improvement of synthesis parameters that can lead to the production of low-cost and highly efficient ZnO:Eu Pdfunctionalized miniaturized gas sensors, selective to H₂ gas, even at room temperature, for personal, industrial, safety and environmental use.

Graphene/oxide composite structures can be employed for advanced applications owing to their synergistic properties. We prepared mesoporous TiO₂ layers including (i) graphene oxide and (ii) reduced graphene oxide at various concentrations. The films deposited on glass were tested for photocatalytic degradation, in water and under UV light, of sulfathiazole, a model compound of an eco-persistent antibiotic. The results show the high photocatalytic activity of the TiO2 layers. Moreover, a significant improvement in the photodegradation rate is found for graphene oxide with an optimum concentration of 2 wt. %. It is assigned to a favorable energy level combination that favors the photogenerated charge separation and increases the lifetime of the electron/hole pairs.

ZnO is a fascinating large gap (3.37 eV) semiconductor, which exhibits intrinsically n-type conductive due to its native defects such as zinc interstitials and oxygen vacancies and such n-type related defects tend to compensate the p-type acceptor defects. However, the generation process of p-type defects is more challenging for developing a good quality homojunction optical device. Here we have studied the effect of ex-situ atmospheric annealing on conductivity of ZnO films. The ZnO films were deposited using RF sputtering on Si substrate temperature at 400°C substrate temperature and 2.2E-2 mbar gas pressure. The films were deposited in oxygen-rich ambient to achieve less oxygen vacancy defects in the film. The ex-situ atmospheric annealing is performed at higher temperature of 900 and 1000ºC. The effects of this postdeposition annealing on the electrical, structural, elemental and optical properties of ZnO thin films were investigated in detail. The X-ray Diffraction (XRD) results exhibited the hexagonal wurtzite structure (002) orientation. After annealing, the XRD peak is shifted at higher 2-thetha value, which indicates a reduction in lattice constant. Further, X-ray photoelectron spectroscopy (XPS) had been done and such XPS results confirmed that simultaneous generation of acceptor defects and reduction of oxygen vacancy related donor concentrations. The electrical properties of films were studied using hall measurement system. These electrical parameters were purposive to inspect the effect of ex-situ atmospheric annealing temperatures on conductivity of films. The Hall measurement confirmed that 1000ºC annealed films achieve p-type conductivity with high reproducibility and such p-type behavior exhibits high mobility. Thus, temperature induced conductivity reversal could be a potential and cost-effective technique to achieve highly stable p-type ZnO films.

We compared spectral response of a PbSe thin film photoconductor using FTIR with either a current or voltage preamplifier from 77K to 340K. The voltage preamplifier had a series load resistor; the current preamplifier did not. A photoconductor’s resistance changes with incident light, thus its measured response in terms of amps or volts per watt of incident light depends on the preamplifier circuit configuration. However, commercial descriptions of spectral response often only present data for a single circuit configuration. This leads to different “apparent” spectral response curves for different circuits with the same device. We investigated how accurately we could predict the response trend of a voltage preamplifier circuit or a current preamplifier circuit using dark resistance (Rdark) and light resistance (Rlight) measurements. We were able to predict the temperature at which maximum response occurs within ~25K, suggesting that this approach can be useful to predict the response of a PbSe photoconductor in various circuits with a limited set of measurements.

The discovery of ferroelectricity in Hafnia (HfO₂) and Zirconia (ZrO₂) in 2011 raises the question of using these materials in photonic applications due to their compatibility with silicon. In this study, we used first-principles calculations to investigate and report on the electro-optic properties of the ferroelectric orthorhombic Pbc2₁ and rhombohedral R3m phases of ZrO₂ and HfO₂. We considered three main contributions to the Pockels effect: electronic, ionic, and piezoelectric. The highest Pockels coefficient of approximately 12 pm/V was found in pure ZrO₂. We discuss the potential ways to increase the electro-optic response of ZrO₂/HfO₂-based materials and the experimental challenges of stabilizing the ferroelectric phase in these materials.

Here we present all-oxide thin film tunable capacitors (varactors) grown epitaxially on silicon substrates, using a SrTiO₃ buffer layer. In the all-oxide varactors, a highly conducting oxide SrMoO₃ bottom electrode is covered with a functional 100nm BaxSr_1−xTiO₃ tunable dielectric layer. A combined Au/Pt layer is used as a top electrode. The microwave properties show a tunability of 2 at 10V bias voltage and a high quality factor Q(0V) = 45 at 1 GHz. Further improvement of the electric performance of the all-oxide varactors is feasible by the optimization of the growth process of the oxide layers and extending the SrMoO₃ thicknesses beyond the skin depth at frequencies relevant for the considered application. The all-oxide varactors on Si are suitable for the high performance agile devices with low tuning voltages and ultra-low power consumption.

With this work we seek to cover a key space in the study of new materials for IR plasmonics: their integration on functional substrates. We show that Cd(Zn)O, a promising semiconductor oxide characterized by its low losses, can be grown in a polycrystalline form on a GaAs substrate. Despite this polycrystallinity, its plasmonic response can be described based on the physics of a homogeneous thin layer. With this study, we validate Cd(Zn)O for future integrated plasmonic systems on GaAsbased photonic devices.

In this study, two different metal electrode patterns are adopted, namely, the straight and curved electrodes, each of which contains 5 different numbers of pairs of interdigitated electrodes. The foregoing design is meant to investigate the resultant photocurrent and dark current magnitudes and the associated hysteresis loops by exposing samples of different numbers of pairs of electrodes to different incident light polarizations. Both linearly and circularly polarized lights are used as incident lights for the measurement of photocurrent. Regardless of its handedness, it is found that the device with curved interdigital electrodes can generate higher photocurrent, vis-à-vis ones with straight interdigitated electrodes. In particular, the device with 8 pairs of curved interdigitated electrodes could have the current enhanced by up to 60%. Finally, among all the photodetectors tested, the highest responsivity of up to 2.15 A/W has also been achieved.

Surface Acoustic Wave (SAW) technique is one of the most promising MEMS-based detection systems for gas sensing. It depends on the modulation of SAW to detect the target gases. The benefits of an acoustic wave hydrogen sensor include high sensitivity, simplicity, stability, quick response time, etc. The SAW sensor converts an input electrical signal into an acoustic wave which can be easily influenced under mass loading. The change in amplitude, phase, frequency or time-delay between the input and output electrical signals can be used to measure the presence of hydrogen. In the present work, the SAW sensor was designed and fabricated for a resonant frequency of 100 MHz on a Lithium Niobate substrate with palladium (Pd) thin film as the sensing layer. The sensor exhibited linear shift in resonant frequency as a function of hydrogen concentration.

This PDF file contains the front matter associated with SPIE Proceedings Volume 12422, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.