Research and development of semiconducting HgCdTe material and devices commenced in 1959 [1]. Due to its outstanding natural properties, such as tuneable band gap and high quantum efficiency, HgCdTe has dominated the high performance end of the infrared detector market for decades. In this paper, we present recent advances in the material growth and device fabrication of HgCdTe infrared imaging focal plane arrays (IRFPAs) at The University of Western Australia (UWA). Also presented are some of the major achievements and future outlook.
It is well known that optical feedback in a laser system, such as the semiconductor laser-based one shown schematically in fig.1, can either stabilise or destabilise its output power and spectral characteristics. Semiconductor lasers have a level of sensitivity to optical feedback that is far greater than most lasers [1-3]. The current interest in using semiconductor laser with optical feedback systems, including versions implemented as integrated devices, in, for example, random number generation, reservoir computing and secure communications [1-3], sustains vigorous research activity in the field. The high, and increasing, potential for making strong connections between the predictions of increasingly sophisticated theoretical models of these complex systems and experimental measurements also reinforces the sustained activity in the field.
A low cost thermography system capable of submilliKelvin resolution has been developed and will be described through this work. The instrument is applied to the study of low thermal conductivity porous silicon films, which is a challenge given that thermography has previously been developed to study only thin (released) films or highly conducting films on insulating substrates. Our preliminary results indicate that the system is capable of measuring porous silicon thin films on highly conducting substrates, but requires application of the pertinent underlying physics for parameter determination.
Power-over-fibre (POF) has been demonstrated for remotely powering microelectronic devices in hazardous environments [1] and in telecommunication and smart grid applications [2]. The technique can also be used for supplying power to surveillance cameras which reduces their vulnerability to tampering [3]. Ultimately, POF will have significant applications in the development and implementation of all-optical sensor networks. However, there is a limit to the amount of power that can be transmitted via the optical fibre due to processes such as stimulated Brillouin scattering (SBS) [4]. As such, the aim of this study is to optimise the power delivered to different parts of an optical fibre network, in order to minimise the effects of processes such as SBS. This can be achieved by enhancing the performance of the photovoltaic microcell (also called a photovoltaic power converter, PPC) and tailoring it to match the power requirements of sensors or actuators scattering throughout the network.
In this work we present the theoretical optical modelling of full width at half maximum and free spectral range of the microelectromechanical systems (MEMS) based based Fabry Perot filters. These filters use silicon and silicon oxide based distributed Bragg reflectors. We also show the impact of variation of silicon thin film properties and structural deformation on the performance of filters. Finally we present fabrication and optical characterization of the fixed cavity SWIR wavelength range FP filters. The fabricated filters showed 39 nm FWHM and above 80% transmittance.
Porosity gradients are a key factor limiting the application of porous silicon (PS) in micromachined structures. In this work, the in-depth porosity profile of PS was studied by measuring the average porosity for samples grown at both constant current density and varied current density; the latter designed to compensate vertical porosity gradient effects. For constant current density, the results showed that the porosity increases from the top surface toward the Si/PS interface. This result is applicable to samples less than 4-μm thick. The varied current density investigations with current density reduced over the duration of anodisation indicated that two recipes at ΔI=10 & 12 mA/cm 2 resulted in a relatively low porosity gradient and low tensile residual stress. Using these two recipes, released MEMS-based PS microstructures were fabricated. The results showed that the recipe using a current density variation of ΔI=10 mA/cm 2 (where Iinitial=20 mA/cm 2 and Ifinal=10 mA/cm 2 ) was the best approach to produce microstructures with a peak to valley (PV) flatness of 200 nm. This study provides a pathway to create released, MEMS-based resonant cavity optical devices using only a single material (Si) platform.
Single crystal isotopically pure 28Si cylindrical Whispering Gallery (WG) mode resonators have been machined from a rod of isotopically pure crystal. Before machining, the rod was loaded into a cavity with the best Bragg confined modes exhibiting Q-factors above a million for frequencies between 10 and 15 GHz. Electron Spin Resonance spectroscopy revealed a very narrow linewidth spin transition, with g-factor of 1.995±0.008. Analysis determined an upper limit to the linewidth of 7 kHz and a concentration of less than 10 11 spins/cm 3 (10 parts per trillion). After machining into WG mode resonators, the measured frequencies of the fundamental mode families were used to determine the relative permittivity of the material near 4 K and 20 mK to be 11.488±0.024, with the precision limited only by the dimensional accuracy of the resonator. However, the Q-factors were degraded to below 40,000. Raman spectroscopy revealed strain induced broadening on the radial surface of the crystal as a result of the machining. After an acid clean and etch, followed by annealing, the surface damage was repaired. Subsequently, high Q-factors were also restored. The next step will be to purposefully implant ions to try and realise narrow linewidth spin ensembles with clock transitions, which will couple to high-Q WG modes inside the crystal.
This paper presents a simple method to extract the damping ratio of bilayer cantilevers using the static deflection profile of the released cantilevers. The extracted damping ratio is used to build a second order dynamical model of the cantilever. The model is validated by comparing the measured step response with the response predicted by the second order dynamical model.
Copper iodide (CuI) is a p-type transparent conductor that can be synthesized and doped at low temperature (≤ 100 °C) while maintaining its high-conductivity and high optical transmittance (> 75 %). The realization of such simultaneously high conductivity and transparency makes CuI useful for applications in both active and passive flexible electronics. However, a few of the major disadvantages of CuI include its optical and electronic stability at ambient atmosphere and reduced transparency with iodine doping. In this report, instead of using pure CuI, we fabricate CuI-TiO 2 composite thin films which are highly transparent and stable at ambient conditions whilst maintaining degenerate p-type conductivity. The CuI-TiO 2 composite film is >80 % transparent (450- 2000 nm range), highly conducting ( ~ 77 S/cm), heavily doped (> 1.2 × 10 20 /cm 3 ), with a mobility of ~ 3.5 cm 2 V -1 s -1 .
we have used the classical Hall Effect to electrically characterize indium tin oxide (ITO) films grown by two different techniques on silica substrates. ITO films have the unique property that they can be both electrically conducting (and to be used for a gate electrode for example) as well as optically transparent (at least in the visible part of the spectrum). In the near infrared (NIR) the transmission typically reduces. However, the light absorption can in principle be compensated by growing thinner films.
Thermal to electrical energy conversation by Seebeck element was enhanced by up to ∼ 50% by dispersing 50nm diameter Au nanoparticles over the black-Si light harvesting surface at an optimized concentration. Size of Au nanoparticles is the defining factor for the spectral position of the extinction maximum at which the cumulative absorption of black-Si (without nanoparticles) can be augmented resulting in an increase of voltage produced by a Seebeck element. Black-Si with reflectivity of 1–2% over the entire visible spectral range is a promising material for extending the operational range of solar and thermal energy converters into longer wavelength regions. Numerical simulations reveal efficient localization of light energy absorption inside black-Si.
Simulations of quantum-dot cellular automata (QCA) on classical computers are highly limited due to the exponential growth in resources required for the numerical simulation of quantum mechanics involving networks of finite state nodes. Recent advancements in computing based on networks of flux-qubits, and in particular the platform technology developed by D-Wave Systems Inc., have made it possible to explore QCA networks that are intractable on classical machines. However, the embedding of such networks onto the available processor architecture is a key challenge in setting up such simulations. In this work, two approaches to embedding QCA circuits are characterized: a dense placement algorithm that uses a routing method based on negotiated congestion; and a heuristic method implemented in D-Wave's SAPI package. Both embedding methods are characterized using a set of basic QCA benchmark circuits of various sizes and complexities. When including diagonal interactions only in the case of an inverter, both methods were able to embed a 4-bit 2-1 multiplexer circuit containing 192 non-driver QCA cells onto the 512 qubit D-Wave Vesuvius chip architecture. Including diagonal interactions for all cells, both methods successfully embedded a serial adder circuit containing 126 non-driver cells.
We have studied the anisotropic Zeeman splitting of ID holes formed on a (100) GaAs/AlGaAs heterostructure on a single cooldown. The strong spin-orbit coupling of holes and ID confinement gives rise to a highly anisotropic spin-splitting. In measuring quantum point contacts on the high symmetry (100) plane, we eliminate the effects of crystal anisotropy on our direct transport measurements of the Zeeman spin-splitting. We find that g||⊥QPC <; g||||QPC <; g⊥ (100) where g|| refers to the in-plane g-factors parallel and perpendicular to the QPC, and g⊥(100) refers to the g-factor perpendicular to the 2D interface. We compare our data with existing theories and show that there are aspects of hole spin-splitting which remain to be understood.
This paper presents the results of experimental work on a low temperature through-wafer reactive ion etching (RIE) technique obtained in the course of development of a process that can be used in small sample processing for microelectromechanical systems (MEMS). Low temperature RIE are a crucial step for many dry MEMS fabrication processes, where can be used to fabricate silicon vias, trenches, and to perform dry release of membranes and other devices. The through-wafer etch developed here can be used also to separate fabricated devices, especially when it is desirable to produce non-rectangular shapes, which cannot be cut using a dicing saw. The presented process works with large silicon wafers as well as with small samples. In this work we developed a method which allows for stabilization of the sample temperature at the correct level during the entire process, which allows through wafer etch of thick silicon samples. The results obtained indicate that there is no universal process suited to all applications. Here we present three different recipes suitable for various applications.
We have studied the electronic transport characteristics of nanowire field effect transistors (NWFETs) made from phase-pure wurtzite (WZ) and zinc blende (ZB) InAs nanowires (NWs). The electronic characteristics were obtained at temperatures between 4 and 300 K. The ZB NWFETs exhibited a greater sensitivity to the surrounding atmosphere than WZ NWFETs. The WZ NWFETs had a higher mobility than ZB NWFETs at a given temperature. We also found that WZ NWs had a higher carrier density than ZB NWs at most temperatures, presumably due to differences in carbon incorporation during growth.
The role of ultra-thin buffer layer of C60 in recently developed high contrast-ratio tandem organic light emitting devices (HCT-OLEDs) is experimentally investigated. The strong photon emission of Al/C60/ N, N'-di(naphthalene-1-yl)- N, N'- diphenylbenzidine/tris8-hydroxyquinoline-aluminum/LiF/Al verifies the efficient hole-injecting role of Al (7 nm)/C60 (2.5 nm). When the applied voltage is higher than 15 V, abrupt drop in current is experienced and the peak of the electroluminescence spectrum vanishes as a result of the phase tuning structure of the HCT-OLED. This demonstrates that the Al/C60 anode performance is unstable under high voltage operation. Such instability causes HCT-OLED power efficiency to drop significantly, necessitating more stable buffer layers to be used instead of C60 in order to realise viable HCT-OLEDs for display applications.
Multicarrier transport planar fully-depleted silicon-on-insulator MOSFETs has been investigated employing magnetic-field dependent geometrical magnetoresistance measurements and high-resolution mobility spectrum analysis. The results indicate that electronic transport in the 10 nm thick Si channel layer is due to two distinct and well-defined electron species. According to self-consistent Poisson-Schrödinger calculations, the two distinct electron species detected correspond to carriers in distinct energy sub-bands arising from strong carrier confinement and volume inversion. The mobility peak of the dominant carrier was found to occur under gate bias conditions that result in a minimum perpendicular effective electric field.
Control of stress in porous silicon (PS) through porosity changes was studied using X-ray diffraction rocking curve measurements. The effect of thermal annealing on the stress was also investigated, which showed the ability to achieve compressive or tensile films in a reversible manner. The effect of stress on the resonant frequency of PS microbeams was studied to understand the impact of PS film stress when used as the structural layer in a microelectromechanical systems sensor. The results indicated that stress is a significant factor in determining resonant frequency, shifting it by up to a factor of 3.6 from the zero stress state, illustrating the need for accurate control.
Electrical contacts between metals and semiconductors are fundamentally important for practical semiconductor devices. This work reports the electrical characterization of nanowire arrays fabricated by a top-down approach, where electron beam lithography (EBL) and a highly anisotropic Cl2/H2/Ar inductively coupled plasma (ICP) reactive ion etching (RIE) is utilised to generate vertical arrays of InP nanowire arrays. Preliminary results show ohmic behavior from these arrays.
