This PDF file contains the front matter associated with SPIE Proceedings Volume 12887, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The heterojunction of polycrystalline Li-doped IrO₂, grown by pulsed laser deposition, and (100)-oriented Si is investigated to develop CMOS-integrated compact optoelectronics. The grown films exhibited p-type conductivity with a bandgap value of around 3.15 eV. Energy-dispersive x-ray spectroscopy mapping confirmed the films’ composition. The hetero-integration of wide-bandgap metal oxides on Si extends the scalability of CMOS-compatible optoelectronics and power electronics, paving the way for enhanced optoelectronic processes and miniaturized photonic circuits.

As an emerging candidate material for photovoltaic applications, metal halide perovskites are well-known for their high power conversion efficiency and fabrication convenience. Mixed-halide perovskites, specifically those with bromide (Br) and iodide (I) anions, are a popular choice for the light-absorbing layer due to their wide bandgap, a critical consideration as perovskite-based tandem solar cells make a major effort towards commercialization. However, the photo-induced halide phase segregation in mixed halide perovskites under illumination can severely damage the device lifetime, so it is of great importance to realize appropriate strategies to slow down or inhibit this photo-segregation phenomenon. In this work, we applied both doping (using Cu and Li-Cu dopants) and surface modification (using two different phosphonic acid-based self-assembled monolayers) strategies to the nickel oxide (NiOx) hole transporting layer (HTL) under perovskite films in solar cell devices to adjust its hole collection capability and carefully examine the photo-segregation process via in situ UV-visible absorption spectrum monitoring. This enables us to elucidate the relationship between the properties of HTL and the photo-segregation process and work towards an optimal HTL. Hole trapping, leading to iodide oxidation and extraction, is a major pathway leading to halide ion mobility. We expect the existence of a HTL can prevent accumulation of holes in the bulk perovskite film and thus slow down the process of photo-segregation. Obtained results for both 2D and 3D mixed halide perovskite films are discussed in detail.

So-called split Ga vacancies, where a next-nearest-neighbor Ga atom relaxes strongly creating a structure with two "half-Ga vacancies" are the main defect observed with positron annihilation in almost all as-grown β-Ga₂O₃, irrespective of doping or conduction type. Unrelaxed Ga vacancies are observed in some samples subjected to high-energy particle irradiation. It also appears to n-type doping with Si promotes the formation of unrelaxed Ga vacancies. In spite of the high concentrations of the Ga vacancy related defects in the as-grown materials, the electrical compensation appears not to be directly affected by the vacancies.

Gallium oxide (Ga₂O₃) is a promising ultra-wide bandgap (UWBG) semiconductor that was quickly recognised as a suitable material for fabrication of optoelectronic devices or high-power rectifiers and switches, potentially greatly exceeding the capabilities of mainstream Si, GaN, and SiC. Despite many advantageous material properties, large-area bulk Ga₂O₃ substrates remain expensive, and Ga₂O₃ itself suffers from low lattice thermal conductivity – crucial for an efficient heat extraction from the active device area, generated by Joule losses during the on-state operating conditions. Heteroepitaxy of Ga₂O₃ films offers a possible route for a low-cost production of Ga₂O₃-based power or optoelectronic devices if e.g. sapphire substrates are used, or much improved thermal performance if highly-thermally-conductive substrates such as SiC or polycrystalline diamond are used. In this work we use liquid-injection metalorganic chemical vapour deposition (LI-MOCVD) to grow thin Ga₂O₃ films on sapphire and 4H-SiC and to fabricate depletion-mode metal-oxide-semiconductor field-effect transistors (MOSFETs). Structural and transport properties of the Ga₂O₃ films and devices prepared on both substrates are analysed. Then, thermal properties of grown Ga₂O₃ films, and Ga₂O₃/SiC and Ga₂O₃/sapphire interfaces are presented and implications for Ga₂O₃-based devices are outlined.

Metal-semiconductor interfaces to Ga₂O₃ have been demonstrated to be highly sensitive to device processing conditions. Liftoff processing leads to inconsistency in ohmic contact formation and quality due to apparent chemical modification of the surface layer, which is not affected by most traditional surface cleanings but can be removed by Ga-flux polishing. Metal-first processing on as-grown material, which avoids exposure of the Ga₂O₃ surface to photoresist prior to metal deposition, has been shown to form reliable, low-resistance ohmic contacts. Investigation of the chemical composition of contacts to material that has been modified by liftoff and cleaned by Ga-flux polishing by x-ray photoelectron spectroscopy (XPS) reveals slight variations in the oxidation states of the Ti and Ga in the contacts that indicate the nature of the surface chemistry modification.

Development of β-Ga₂O₃ power devices has been accelerating over the past few years. In particular, 4-inch device-quality β-Ga₂O₃ epi wafers have become commercially available, and low-loss trench MOS-type SBDs, and normally-off MOSFETs have been demonstrated. In this paper, we will explain recent progress in crystal growth techniques for β-Ga₂O₃ and power devices based on this material.

β-Ga₂O₃ is an ultrawide bandgap semiconductor that shows promise for high-power, deep-UV, and extreme environment applications. Hydrogen can affect the conductivity of β-Ga₂O₃ through the introduction of shallow donors and the passivation of deep acceptors. This work is a study of the interaction of H with VGa deep acceptors as well as other impurities in β-Ga₂O₃ by IR spectroscopy and complementary theory.

We report on the growth and characterization of κ-Ga₂O₃ films grown at varying temperatures in the range of 450-700 ˚C by mist-CVD. All of the films are single-crystalline and phase-pure except for the two samples grown at 550 ˚C and 600 ˚C, which have (2̅ 01)-oriented β-Ga₂O₃ incorporated in them. Unlike the phase-pure films which exhibit hexagonal-shaped grains, the mixed-phase samples have rough and partially coalesced films with irregular-shaped grains due to the presence of two Ga₂O₃ phases growing along two different crystallographic orientations. Moreover, we found that annealing the κ-Ga₂O₃ films at 700 ˚C in ambient air led to improved crystalline quality and reduced grain size.

Gallium oxide is being widely studied, mainly for high-power electronics applications. It is a very promising material for photonic/optoelectronic applications, such as solar-blind UV detectors and light emitters. In this work, we study the temperature-dependent behavior of the optical properties of microcavities based on luminescent β-Ga₂O3:Cr nanowires that emit an intense red-infrared band. Two distributed Bragg reflectors (DBR), when milled with a focused ion beam (FIB) and separated some microns, result in an optical microcavity that confines the light longitudinally. Both chromium R lines and Fabry-Perot spectral resonances (FPSR) are observed to shift as temperature varies, making these DBRs a valuable thermometer in a wide temperature range, due to both luminescent and interferometric transducing mechanisms. The underlying origin of this shift, in the case of the FPSR, is mainly the variation of the refractive index with temperature and the thermal expansion of the cavity. Ellipsometry studies carried out at different temperatures in bulk β-Ga₂O₃ yielded the dispersion relations for the three main crystal axes, i.e. its temperature-dependent anisotropic refractive index. These results were implemented in finite-difference time-domain (FDTD) simulations to compare the expected spectral shift of the FPSR in the modelled system with the experimental shift in the DBR cavities, as obtained experimentally by micro-photoluminescence. The results from these two approximations, and a third one based on solving the relevant analytical equations, are compared.

An accurate modeling of the current conduction through the gate stack is needed to identify the residual conduction paths, to improve the behavior of the device in future iterations of the technological process. Models available in the literature are applied to the study of experimental gate leakage measurements in gallium oxide MOSFETs in a wide temperature range, from cryogenic temperature up to 350 K. Experimental results show a dominant Poole-Frenkel mechanism at high temperature and high bias, and Fowler-Nordheim tunneling at low temperature. A suitable rate equation was developed to model the time-dependent behavior of the gate leakage with applied bias. The gate leakage model was implemented in TCAD, and is able to reproduce the experimental behavior from the milliseconds to the hundreds of seconds range.

Gallium Oxide (Ga₂O₃) has attracted great attention due to its predicted high critical electric field, and consequentially its expectation to have impact for high voltage power devices. However, from a device design and reliability perspective, it has certain drawbacks: Ga₂O₃ has a relatively low thermal conductivity, potentially causing excessively high device temperatures, accelerating device degradation; usable p-doping is unavailable, preventing the use of advanced devices designs such as superjunctions which require both n- and p-doping. It is critically important to address these limitations for Ga₂O₃ to compete with SiC which is Ga₂O₃’s direct competitor, where advanced device concepts such as superjunctions are in process being explored, and prototype devices have already been realized. For Ga₂O₃, one possible solution is heterogeneous integration with other wide or ultra-wide bandgap materials which can be p-doped. Selecting materials with higher thermal conductivity would also address thermal management. Nickel Oxide has been explored as a p-type material and successful Gallium Oxide / Nickel Oxide high voltage proto-type devices have been demonstrated. However, Nickel Oxide’s has a low thermal conductivity, so enabling devices which can handle high current densities may be a challenge. Based on these criteria, diamond and SiC are primary candidates for integration with Ga₂O₃. We report here on integration by metal organic chemical vapor deposition (MOCVD) of Ga₂O₃ with diamond and SiC. We also explore direct bonding as an alternative heterogenous integration method.

We report the miniaturization of Ag/BiFeO₃/ITO resistive random access memory (ReRAM) in the form of long-period waveguide grating, all fabricated entirely on z-cut lithium niobate (LiNbO₃) substrate. The electric characterization vividly reveals a selector-like threshold-switching (TS) characteristic. It is well accepted that there are two filament formation mechanisms governing the operation of Ag/BiFeO₃/ITO ReRAM, a two-side TS characteristic is typically generated when the positive and negative bias voltages are applied during the cycles. It is reasonable to believe the TS characteristic exists because the Joule heat produced during device operation cannot be dissipated effectively, resulting in the rupture of the conductive filament. To mitigate this shortcoming, replacing the BiFeO₃ (BFO) layer of the original grating shape with a planar-layer structure is beneficial for heat dissipation, and this, in turn, would help to improve the characteristics of the ReRAM device by delivering the memory-switching characteristics as intended. As already mentioned, this ReRAM structure with the ITO bottom electrode fabricated over the lithium niobate waveguide can jointly serve as the long-period waveguide grating. Furthermore, when the Ag/BFO/ITO ReRAM structure's device area shrinks to 200 μm², the growth path of the silver conductive filament is confined immediately above the lithium niobate waveguide. The corresponding spectral measurement shows that as the increasing number of ReRAM grating fingers are in the set state (silver conductive filaments formed), the energy of the transmission dips would decrease gradually in return, and during the reset state, the energy of the transmission dip would rise accordingly.

The top cladding is an important factor when designing photonic devices. It has implications on waveguide properties such as mode guidance and optical loss. Silicon dioxide (SiO₂) is a commonly used cladding material for photonic devices as it has low optical loss and also enables a large refractive index contrast between the waveguide core and cladding. We performed an investigation into the material properties of SiO₂ thin films deposited by different methods, namely, plasma-enhanced chemical vapor deposition (PECVD) undoped silicate glass (USG), high density plasma (HDP), PECVD tetraethyl orthosilicate (TEOS), and low pressure chemical vapor deposition (LPCVD) TEOS. Material properties including refractive index, surface roughness, absorption, and film stress were characterized for the different SiO₂ cladding samples. Our results show that the surface roughness of HDP films was around 55 times better than that of USG films. In terms of film stress however, USG films had the lowest, whereas PECVD TEOS films were found to have the highest film stress, more than twice of that of the USG films. These findings indicate that when deciding on a particular deposition method for the SiO₂ cladding, besides considerations of thermal budget and device application, an equally important compromise needs to be made to give a balance among the various material properties.

In this study, three different shapes (traditional, spiral, and enclosed) of interdigitated electrodes are designed and implemented on BFO photodetectors (PD). The electrode material used is indium tin oxide or ITO. As the dielectric layer, BFO is sputtered onto the silicon substrate via a radio frequency magnetron sputtering machine and annealed with a furnace tube. Eight experiments are planned according to the procedures set forth by the binary design of experiments (DOE) to optimize the PD fabrication steps. The three process parameters contemplated are annealing gases (nitrogen or oxygen), annealing temperature (300 and 550ºC), and sputtering argon flow rate (5 and 10 sccm). It can be found that regardless of the shape of interdigitated electrodes used, the responsivity and detectivity obtained from Run 3 (annealing temperature of 300ºC, argon flow of 10 sccm, and nitrogen annealing gas) are relatively large. In contrast, the corresponding values are all comparatively small in Run 5 (annealing temperature of 300ºC, argon flow of 5 sccm, and oxygen annealing gas). Furthermore, the interaction between the annealing temperature and the different annealing gases, as well as the argon flow alone, have noticeable influences on the responsivity and detectivity of the BFO photodetectors with the traditional interdigitated and spiral interdigitated electrodes. As for the PDs with the enclosed electrodes, the interaction between the annealing temperature and the different annealing gases also undeniably impacts the resultant responsivity and detectivity.

The development of solar cells with a low ecological footprint requires the optimization of semiconductor thin films having different and complementary optoelectronic properties: transparent electrode (TCO: transparent conductive oxide), window, buffer and absorber layers. Oxide semiconductors have two crucial advantages for this purpose: they can be developed using low-cost techniques such as ultrasonic spray pyrolysis (USP), and their optoelectronic properties can be extensively modulated through the chemical composition to adapt them to each of the layers. ZnMgAlO thin films have been developed by USP by optimizing the most impacting growth parameters: concentrations and pH of the precursors solution, substrate temperature, flow rate, nozzle speed, dwell time and shaping air pressure. In addition, a post-deposition annealing process has been developed by optimizing the annealing temperature, duration and nitrogen flow. The thickness can be easily adjusted by the deposition parameters from 50 nm to 700 nm and films investigated in the present study have a thickness of 200 nm. X-ray diffraction (XRD) analysis evidenced single-phase wurtzite structure with a strong preferred <002> orientation. A grain size varying from 40 nm to 70 nm was achieved, thus being in the upper range of the state of the art. Optical transmission results are well correlated with XRD data and indicate the bandgap increases linearly with the magnesium composition, an Urbach energy of about 70 meV, and a transparency of more than 90 % in the visible region. A Mg-modulable electrical resistivity of 10⁻² Ω · cm to 10² Ω · cm was obtained with a mobility of approximately 5 cm²V⁻¹s⁻¹. The incorporation of aluminum into ZnMgO was achieved for the first time by USP and making possible to adjust the resistivity for application as a TCO. These results show the full potential of ZnMgAlO for application in all-oxide solar cells.

Layer transfer technique of epitaxial (00l) oriented rutile TiO₂ films sputtered on sapphire substrates using epitaxial ZnO sacrificial layer was developed. It was demonstrated that obtaining an epitaxial structure for rutile layer transfer can be challenging, due to required control of variety of parameters – surface roughness, growth rate, deposition temperature, interface stresses and lattice matching. It was shown that ZnO, directly grown on M-sapphire substrates, promotes polycrystalline rutile growth. Therefore, 50 nm thick (00l) rutile seed layer with controlled surface roughness grown on M-sapphire substrate was needed to promote the epitaxial (101" 3) ZnO growth, which then allowed to obtain epitaxial (00l) rutile layer suitable for the layer transfer process. The examined structural quality, evaluated by means of X-ray diffraction and Raman spectroscopy, showed that the transferred rutile films exhibit promising properties for photonic applications.

The conducting properties of crystal topological insulators and Weyl semimetals within the plasma mechanism of superconductivity have been considered. Such compounds A2B3, AB2, AB are bismuth selenide Bi2Se3 and telluride Bi2Te3, antimony telluride Sb2Te3 and their solid solutions, tungsten telluride WTe2, magnesium diboride MgB2, tantalum arsenide TaAs, tantalum phosphide TaP, niobium arsenide NbAs, niobium phosphide NbP. The equation has been proposed 2 AB = A2 + B2 + ▴Φ. Square plasma electron energies Φ² (ρ, s, M, q, β), square electron splitting energies ▴Φ² in (eV)² were calculated, where Φ² (ab), Φ² (a), Φ² (b) – square electron energy AB, A, B, ▴Φ² is square energy splitting of compounds into diatomic molecules at absolute zero Tc = 0, respectively, ρ is the density, s is the number of valence electrons, M is the molecular (atomic) mass, q and β are parameters. ▴Φ² (Bi2Se3) = 765.70143384 ▴Φ² (Bi2Te3) = 672.88715592 ▴Φ² (Sb2Te3) = 704.74855610 ▴Φ² (WTe2) = 367.01888428 ▴Φ² (MgB2) = 435.17777627 ▴Φ² (TaAs) = ▬102.44793138 ▴Φ² (TaP) = ▬246.35400903 ▴Φ² (NbAs) = ▬83.59742866 ▴Φ² (NbP) = ▬241.26056837. β = 2.5, q (Bi2Se3) = 1.02608569, Tc = ▬ 7.3039932 K β = 2.5, q (Bi2Te3) = 0.997794409, Tc = 0.61756548 K β = 2.5, q (Sb2Te3) = 1.015846129, Tc = ▬ 4.43691612 K According to our calculations, superconductivity of doped A2B3 topological insulators was found above absolute zero temperature. Additional restrictions are caused by strong spin-orbit coupling. Theoretical calculations are confirmed by known experimental data.

p-NiO/n-Ga₂O₃ heterostructures were formed on single crystal (-201) β (monoclinic) Ga₂O₃ and r-sapphire substrates by Pulsed Laser Deposition. Ring mesa layer stacks were created using a shadow mask during growth. X-Ray diffraction studies were consistent with the formation of (111) oriented fcc NiO on the bulk Ga₂O₃ and randomly oriented fcc NiO on (102) oriented β-Ga₂O₃/r-sapphire. RT optical transmission studies revealed bandgap energy values of ~3.65 eV and ~5.28 eV for the NiO and Ga₂O₃ on r-sapphire. p-n junction devices were formed by depositing gold contacts on the layer stacks using shadow masks in a thermal evaporator. Both heterojunctions showed rectifying I/V characteristics. On bulk Ga₂O, the junction showed a current density over 16mA/cm² at +20V forward bias and a reverse bias leakage current over 3 orders of magnitude lower at -20V (1 pA). On Ga₂O₃/r-sapphire the forward bias current density at +15V was about an order of magnitude lower than for the p-NiO/bulk n-Ga₂O₃ heterojunction while the reverse bias leakage current at -15V (~ 20 pA) was an order of magnitude higher. Hence the NiO/bulk Ga₂O₃ junction was more rectifying. Upon illumination with a Xenon lamp a distinct increase in current was observed for the IV curves in both devices (four orders of magnitude for -15V reverse bias in the case of the p-NiO/bulk n-Ga₂O₃ heterojunction). The p-NiO/n-Ga₂O₃/r-sapphire junction gave a spectral responsivity with a FWHM value of 80nm and two distinct response peaks (with maxima at 230 and 270nm) which were attributed to carriers being photogenerated in the Ga₂O₃ underlayer. For both devices time response studies showed a 10%/90% rise and fall of the photo generated current upon shutter open and closing which was relatively abrupt (millisecond range), and there was no evidence of significant persistent photoconductivity.

In optics, inorganic coatings such as TiO₂, ZrO₂, HfO₂, La₂O₃, and Ta₂O₅ surpass their organic or hybrid counterparts in terms of performance. They have the highest refractive index and remain unaffected by environmental degradation issues like yellowing. However, existing methods for creating inorganic coatings are limited to two approaches. The first involves costly and time-consuming techniques like physical vapor deposition (PVD) or chemical vapor deposition (CVD). The second approach, sol-gel synthesis, necessitates high temperatures that are incompatible with many substrates, resulting in rough surfaces and cracked samples. Phosio has introduced a platform technology for producing inorganic coatings with tunable refractive indices (ranging from n=1.30 to n=2.35). These coatings possess atomic smoothness and require minimal processing temperatures as low as 150°C. Furthermore, these materials can be cured with UV light and are compatible with nanoimprint lithography, all while maintaining environmental stability. In this manuscript, we share our journey to the process of achieving increased film thickness while ensuring the absence of cracks.

In this report, we present a remarkably sensitive and stable gas sensor based on solution-processed p-type copper aluminum oxide (CuAlO₂), which can sense O₃ gas at room temperature. In addition, the sensitivity can be further enhanced through exposure to ultraviolet (UV) radiation. The optimal gas response of 12.32 can be achieved under UV illumination of 20 mW/cm² at room temperature. More importantly, the CuAlO₂ sensor exhibits outstanding long-term stability, with a deterioration of only ~10% over a period of 90 days. These results strongly suggest that solution-processed CuAlO₂ is a promising candidate for gas sensors designed to operate at room temperature.

Heterogenous photocatalysis has emerged as a sustainable and environmentally benign strategy since it converts solar energy into chemical energy. Though more research is exploring the magnetic field effect on photocatalysis, the mechanism is still ambiguous. Magnetic field-assisted and electric-assisted photocatalytic reactions were investigated in this study. In the first magnetic field-assisted experiment, the magnetic field effect on heterogenous photocatalysis was explored with TiO₂ and Pt/TiO₂. Isopropanol photocatalytic oxidation reaction was conducted. Two levels of dissolved oxygen concentration, magnitude of magnetic flux density and temperature were studied. The magnetic field positive effect was prominent, especially under higher dissolved oxygen concentration and greater magnitude of a magnetic field. For Pt/TiO₂ photocatalyst at 10°C and dissolved oxygen concentration over 20 ppm, 450 Gauss increased isopropanol photooxidation by 10%, while 900 Gauss enhanced by 21%. For TiO₂ photocatalyst at 10°C dissolved oxygen concentration over 20 ppm, 450 Gauss has no prominent effect, while 900 Gauss enlarged 18% isopropanol photooxidation. The statistical analysis demonstrated that dissolved oxygen with magnetic flux density interaction and DO were the top two influencing elements. The hyperfine mechanism results from the interaction between the electron spins with nuclear spins in atoms. It depends on the elements and the dwelling time of unpaired electrons with its nucleus. The mechanism would contribute to singlet (S) ⇄ triplet (T) intersystem crossing. It was possibly because the net Lorentz force acting on paramagnetic oxygen molecule and singlet-triplet intersystem crossing by magnetic field led to the enhancement of the photooxidation of isopropanol.

Within electron plasma model, a complex crystal of ABСD as a result of phase separation into four subsystems is considered. During the phase transition in the ABCD crystal, the valence bond breaking associated with the crystal lattice destruction. It is caused by the balance energies of the A-B-C-D and A-A, B-B, C-C, D-D bonds. The basic principle of the phase transition is caused by bonds being broken and dumbbell configurations of atoms are formed. The pairing of electrons is guided by a plasma mechanism. Free electrons couple to lower system energy. When molecules are formed from individual atoms by dumbbell configuration, energy is released. The energy balance is caused by a change in the distances between atoms A-A, B-B, C-C, D-D, with decreasing temperature. It is necessary, that square electron dense plasma energy in the initial phase was essentially much less, than the one in the local phase. This is the condition for the superconducting phase transition in the crystal ABCD. The electron dense plasma parameters in crystals Pd7Se2, Cu3Au, GeNb3, FeSe, MgB2, YBa2Cu3O7, Bi2Sr2Ca2Cu3O10+x, Tl2Ba2Ca2Cu3O10, HgBa2Ca2Cu3O8+x were calculated. q (abcd) = 2β Φ² (abcd) / (Φ²(a)+ Φ²(b)+ Φ₂(c)+ Φ²(d)), where parameters are square Φ² (M, ρ, s, q, β), square Φ² (аbcd), square Φ² (а), square Φ² (b), square Φ² (c), square Φ² (d) are square electron energy in square eV² crystal abcd, a, b, c, d respectively, Tc is the phase transition temperature, ρ is density, s is valence electron number, M is molecular (atomic) mass, q and β are interaction constants. The equations of the superconducting phase transition curve Tc (q) are derived within the known experimental data and our theoretical parameters. A method for finding the phase transition temperature of a crystal was proposed. From the Tc (q) equation, the parameters of superconductors CuS, LiFeAs, complex oxides of titanium and bismuth, taking into account doping with SrTiO3, BaTiO3, Li2TiO3, BaBiO3, BaKBiO3, were determined.

In this work, zinc oxide (ZnO) and tungsten trioxide (WO₃) thin films were grown by a pulsed laser deposition (PLD) technique at an elevated substrate temperature of 400ºC. The PLD technique involves using a high-intensity laser to vaporize and deposit material onto an n-type silicon (Si) substrate. The field emission gun scanning electron microscopy (FEG-SEM) was employed to visualize and characterize the morphology of the two samples viz., ADW4 and ADZn4. The grazing incidence x-ray diffraction (GIXRD) was used to assess the crystallite structure of the two thin films based samples. The study found that ADW4 exhibited a significantly smaller average crystallite size (6.48 nm) compared to ADZn4 (16.22 nm). The smaller crystallite size of ADW4 is noteworthy and indicates the potential presence of quantum confinement effects, which are crucial in the development of optoelectronic devices such as light-emitting diodes (LEDs), and photodetectors. The room-temperature photoluminescence (RTPL) emission peak for ADW4 and ADZn4 was found to be at 323 nm (3.84 eV) and 379 nm (3.27 eV), respectively, under an excitation wavelength of 300 nm. The RTPL spectra revealed that the peak at around 323 nm for ADW4 gradually shifted towards the ultra-violet (UV) region compared to ADZn4 (379 nm). Significantly, such blue emission is shifted towards the UV-A region in ADW4 suggesting that it could be used to produce UV-A LEDs, which have applications in disinfection, water purification, and UV curing processes.

ZnO layers were grown on (100) and (111) oriented YSZ substrates by pulsed laser deposition (PLD). X-ray diffraction studies revealed growth of wurtzite ZnO with strong preferential (0002) orientation. The ZnO layer on YSZ (111) showed distinct Pendellosung fringes and a more pronounced c-axis orientation (rocking curve of 0.08°). Atomic force microscopy revealed RMS roughnesses of 0.7 and 2.2nm for the ZnO on the YSZ (111) and YSZ (100), respectively. YSZ was then grown on the ZnO buffered YSZ (111) substrate by PLD. XRD revealed that the YSZ overlayer grew with a strong preferential (111) orientation. The YSZ/ZnO/YSZ (111) top surface was temporary bonded to an Apiezon wax carrier and the sample was immersed in 0.1M HCl so as to preferentially etch/dissolve away the ZnO underlayer and release the YSZ from the substrate. XRD revealed only the characteristic (111) peak of YSZ after lift-off and thus confirmed both the dissolution of the ZnO and the preservation of the crystallographic integrity of the YSZ on the wax carrier. Optical and Atomic Force Microscopy revealed some buckling, roughening and cracking of the lifted YSZ, however. XRD suggested that this may have been due to compressive epitaxial strain release.