Semiconductor Infrared Devices and Applications

Infrared (IR) technologies—from Herschel’s initial experiment in the 1800s to thermal detector development in the 1900s, followed by defense-focused developments using HgCdTe—have now incorporated a myriad of novel materials for a wide variety of applications in numerous high-impact fields. These include astronomy applications; composition identifications; toxic gas and explosive detection; medical diagnostics; and industrial, commercial, imaging, and security applications. Various types of semiconductor-based (including quantum well, dot, ring, wire, dot in well, hetero and/or homo junction, Type II super lattice, and Schottky) IR (photon) detectors, based on various materials (type IV, III-V, and II-VI), have been developed to satisfy these needs. Currently, room temperature detectors operating over a wide wavelength range from near IR to terahertz are available in various forms, including focal plane array cameras. Recent advances include performance enhancements by using surface Plasmon and ultrafast, high-sensitivity 2D materials for infrared sensing. Specialized detectors with features such as multiband, selectable wavelength, polarization sensitive, high operating temperature, and high performance (including but not limited to very low dark currents) are also being developed. This Special Issue highlights advances in these various types of infrared detectors based on various material systems

Single-source pulsed laser deposition of hybrid halide perovskites for solar cells

The world is rapidly shifting towards renewable and sustainable energy as we face concerns about climate change. In such times, the abundant energy from the sun is crucial in aiding this transition. The devices responsible for the conversion of solar energy into electricity are termed solar cells. Nowadays, the well-established photovoltaic (PV) industry belongs to silicon PV. Nevertheless, new materials are being researched to complement silicon PV technologies. Metal halide perovskites (MHPs) are one of the emerging solar cell technologies that have fascinated researchers due to their versatility in terms of both composition and fabrication methods, delivering power conversation efficiencies in pair-to-crystalline silicon cells, making them one of the best candidates for the next generation of photovoltaics. The construction of these emerging solar cell devices involves heterostructures containing an absorber material sandwiched between carrier-selective layers and electrodes. Challenges remain regarding upscalable fabrication methods compatible with integrating complex perovskite materials within heterostructures. Therefore, one of the main challenges addressed by the research within this PhD is the demonstration of an alternative physical vapor deposition (PVD) method known as pulsed laser deposition (PLD) for the growth of MHPs. The main motivation to employ PLD for growing MHPs is its unique capability to transfer highly complex chemical compositions from a single-source target to the substrate or a partial solar cell stack. In this thesis, we have demonstrated the utility of PLD as an alternative PVD method for depositing complex MHP thin films with precise stoichiometry. Notably, this method exhibits compatibility with heterostructures and potential for scalability. This compatibility can be further enhanced by improving the hardware configuration of the PLD for wafer-scale area coatings and superior deposition rates. Additionally, we demonstrate PLD as an appealing deposition method for studying the growth of low- and wide-bandgap MHP. These materials pose challenges with alternative deposition methods due to constraints regarding the solubility of different precursors, varying solvent evaporation rates, or difficulties in reproducibility arising from the need to control four or more sublimation sources with significant differences in volatilities. <br/

Coupling of strain and magnetism in manganite-based complex oxide heterostructures

Complex oxide thin films and heterostructures offer a wide range of properties originating from the intrinsic coupling between lattice strain and magnetic/electronic ordering. This article reviews experimental, phenomenological, and theoretical analyses of the coupling of strain with electronic and magnetic properties of mixed valence manganite heterostructures. The influence of epitaxial strain on the magnetic properties of manganite films is measured using macroscopic magnetization measurements and shown mixed reports suggesting, both, an increase and decrease in ferromagnetic phases on the application of the strain. Using polarized neutron reflectivity (PNR), a simultaneous measurement of transport and magnetic properties of manganite thin films showed direct evidence of modification in the magnetic properties on the application of bending strain. The coupling coefficient of strain and magnetism of manganite heterostructures was estimated using PNR, which not only helped to understand the correlation of elastic strain with magnetism but also explained the condition of magnetic phase order change in the phase-separated systems within a phenomenological Ginzburg Landau theory. An overview is also provided of the current perspectives and existing studies on the influence of strain on structure, electronic, magnetic, magnetic anisotropy, phase coexistence and magnetocaloric properties of mixed valence manganite heterostructures. Based on the understanding of a diverse range of perovskite functionalities, detailed perspectives on how the coupling of strain and magnetism open up pathways toward the emergence of novel device design features including the different ways of applying uniform strain, are discussed.Comment: arXiv admin note: text overlap with arXiv:1509.00912, arXiv:1009.4548 by other author

Epitaxial PbZrxTi(1-x)O3 bilayers grown on silicon; giant electromechanical effects and their origin

This thesis investigates the crystallography, domain morphology and electromechanical behaviour of epitaxial PbZrxTi(1-x)O3 (PZT) bilayer heterostructures deposited on silicon. As a first step, PZT bilayers are deposited on SrTiO3 crystalline substrates by pulsed laser deposition, and their high temperature crystallography is investigated by X-ray diffraction (XRD). The profile of rhombohedral and tetragonal PZT structures with temperature shows excellent bulk-like behaviour with clear crystallographic phase transformations and coefficients of thermal expansion that are comparable with literature. Comparisons to theoretical relaxed films reveal how strain within the system is enough to modify the thermal properties of the films including increasing the Curie temperature for extended operation temperatures in practical applications. Next, thin films of tetragonal PbZr0.3Ti0.7O3 (PZT-T) of varying thickness are deposited above a 40 nm rhombohedral PbZr0.54Ti0.46O3 (PZT-R) film, all grown on silicon (100) substrates. XRD is performed on the samples and compared to the crystallographic dataset for bilayers on SrTiO3 substrates. XRD and transmission electron microscopy provide evidence that the PZT-T layer has a modified, pseudo-tetragonal structure due to substrate induced strain but maintains its in-plane a-axis orientation. The structure is observed to pass through a ferroelectric-paraelectric phase transformation with an increased Curie temperature. The domain morphology, characterised by piezoresponse force microscopy, reveals that the unequal lattice parameters of the pseudo-tetragonal structure are insufficiently different to reorient the polarisation. Instead, the film is arranged as ferroelastic a1/a2 tetragonal nanodomains within a larger array of mosaic superdomains. This remains unchanged with reduced film thickness, except for a smaller periodicity of the a1/a2 twins. Interestingly, the domain pattern gives rise to a series of topological defects including vortex/anti-vortex pairs at the surface and multi-phase coexisting core structures within the bulk of the PZT-T film. Finally, the electromechanical properties of the thin films on silicon are investigated, in both an out-of-plane and in-plane configuration. Ferroelectric polarisation switching experiments show a square hysteresis loop of saturation ~32 μC/cm2 and clear capacitance switching peaks. The experiments show that capacitance is doubled when measured in-plane, compared to out-of-plane, since ferroelectric properties are a function of electrode spacing, rather than film thickness, which can be three orders of magnitude larger. Single frequency piezo-hysteresis loops provide evidence of a ~250% improvement of the effective d33 response compared to a standard rhombohedral PZT film on SrTiO3 substrate. This is attributed to the coexisting multi-phases and mobile topological defects which demonstrate the ability to migrate the film surface or annihilate one another in the presence of a local bias. An improvement of this magnitude demonstrates the opportunity to implement bilayer technology while exploiting a functional silicon substrate for enhanced, industry-ready, smart material applications

High-Temperature Photovoltaic Effect in Heterojunction

We fabricated a heterojunction of La0.4Ca0.6MnO3/SiO/n-Si and investigated its electronic transport and ultraviolet photovoltaic properties at higher temperature up to 673 K. The rectifying behaviors vanished with the energy-band structure evolvement from 300 to 673 K. Under irradiation of a 248 nm pulse laser, the peak values of open-circuit photovoltage and short-circuit photocurrent decreased drastically. This understanding of the temperature-related current-voltage behavior and ultraviolet photodetection of oxide heterostructures should open a route for devising future microelectronic devices working at high temperature. PACS: 73.40.Lq, 71.27.+ a, 73.50.Pz