Photonic device package design, assembly and encapsulation

This paper presents a novel rectifier array for a wide dynamic range of RF-dc conversion. The rectifier array consists of multiple rectifier cells optimized for operation at different power levels and uses an adaptive power distribution method to divide the RF input power among these rectifier cells according to the RF power levels. The adaptive power distribution takes advantage of the power-dependent input impedances of the rectifier cells and is implemented with passive devices. This method both improves the rectification efficiency and minimizes the impedance mismatch as the input power level varies, and therefore, significantly enhances the dynamic range. The rectifier array can be designed using either the same type or different types of rectifying devices and can be expanded by including more cells in the network to further increase the dynamic range. In this paper, three different implementations of such rectifier array circuits are described, including a two-diode rectifier array designed with the same type of diodes, a two-diode rectifier array designed with different types of diodes, and a three-diode rectifier array with different types of diodes. The performances of these circuits are validated with measurement and compared with each other. Significant enhancement of dynamic range over conventional rectifiers is demonstrated.

A novel pulse generator scheme using a fast recovery pseudospark switch and a stack of high-power semiconductor diodes was tested. The prototype pulse generator is able to drive capacitive loads of over 150 nF, at peak voltages of up to 40 kV, pulse duration of 6 to 15 /spl mu/s (FWHM, full width at half maximum), and repetition rates of up to 80 pps. Nominal pulse current is between one and 1.5 kA peak. The main limitation in lifetime is caused by the high peak current load in the semiconductor diodes during flashover in the ESP. Diode current can reach up to 8 kA in some cases. A variety of different types of diodes has been investigated, with different physical constructions, i.e. fast high-power press-pack types as well as smaller type, fast, stud-mount diodes. Although the larger press-pack diodes experienced a considerably longer absolute lifetime in these experiments as expected, the comparison of lifetime versus current/charge density on the chip reveals advantages of the stud-mount design (with the diode chip soldered to the substrate) over the press-pack design. The experimental results are discussed in terms of an optimization strategy to achieve the highest power density at minimum cost and volume.

Advances in infrared (IR) detector technologies over the last decade have led to compact low-cost thermal imaging systems that have become almost ubiquitous. They are now used in such market applications as automotive, security and construction. Terahertz (THz) imagers can take advantage of the state-of-the-art in the infrared domain to reduce their size and cost. Such an example is the IRXCAM-THz-384 Terahertz camera whose electronics core is based on the IRXCAM camera core and whose detector has been specifically designed and optimized for the THz. The 384 x 288 35- micron-sized pixel detectors of both cameras are uncooled microbolometers. A micro-electronics core is currently being developed for both platforms that will yield ultra-compact IR and THz cameras. While IR systems are passive and thus do not require an illumination source, the THz system does. Thus, the THz source must be included when talking about overall imaging system size and cost. There are a wide variety of THz sources, from quantum cascade lasers on the optical side of the radiation spectrum to different types of diodes on the electromagnetic micro-wave side. When considering a source for a given application, the output wavelength, output power, size, weight and cost are primary factors that must be taken into account. This paper presents a description of a compact real-time imaging system at 750 μm wavelength. An overview of the motivation for the wavelength choice is discussed, a description of the imaging components is given and finally image results are presented.

The present and the potential performances of opto-electronic elements such as a laser diode (LD), a photo diodes (PD) and an optical waveguide for optical interconnects are described. The fabrication and the integration technologies of the opto-electronic chips are also mentioned. The topics to be highlighted include: (1) the state of the art of vertical cavity surface emitting laser diodes for optical interconnects, (2) the performance analysis of the optical interconnects with integrated optical waveguides and free space optics, and (3) opto-electronic integration technology: hybrid-integration technique, receiver and transmitter design for on-chip and intra-chip optical interconnects.

Organic semiconductor-based solar photovoltaic cells and sensors are scalable, printable, solution processable, bendable and light-weight. Furthermore, organic semiconductors require low energy fabrication process, hence can be fabricated at low cost as light-weight solar cells and sensors, coupled with the ease of processing, as well as compatibility, with flexible substrates. Organic semiconductors have been identified as a fascinating class of novel semiconductors that have the electrical and optical properties of metals and semiconductors. The continuous demand to improve the properties of organic semiconductors raises the quest for a deep understanding of fundamental issues and relevant electronic processes. Organic semiconductor thin film is sandwiched between two metal electrodes of indium tin oxide (ITO) and aluminum to form organic photovoltaic solar cell. Several types of organic semiconductors have been utilized as the photoactive layer in the solution processable organic solar cells. The performance of the fabricated solar cells can be improved by dissolving the material in the right choice of solvent, annealing of organic thin film, slowly forming the thin film and introducing an infra-red absorbance layer. Besides, organic semiconductor-based sensors can be fabricated utilizing either in a sandwidch type or planar type device. Some of these techniques and the experimental results are presented.

The photoelectric effect has been utilized in a wide range of optoelectronic sensors and solar energy conversion devices. To respond to today’s colossal energy demand there is a need for doing better than using this effect via the utilization of simple semiconductor homojunction based devices, since such structures cannot use all photons available for conversion into electricity. Actually, it is the inefficient response of the material to the various solar photons and the behaviour of photo-generated carriers that bar photovoltaic (PV) cells from fully harvesting the solar energy impinging on its surface. It is well known that there is no semiconductor that can be deployed for making a simple and low cost p-junction based solar cell that converts the entire solar spectrum. Hence, the development of efficient photovoltaic devices has been going through various technology pathways, one of which has led to a variety of multi-junction and cell stacks, i.e., tandem cells; each sub-cell is dedicated to converting a portion of the solar spectrum. Moreover, the conventionally chosen three sub-cell tandem scheme is being extended to stacks with larger number of subcells, regardless of the viability of the production technology. During the last five decades, several theoretical PV energy conversion efficiency thresholds have been established, each being for one type of PV device design. However, none has been reached in spite of the deployed tremendous efforts; the implementation turns out to be challenged by some specific constrains. High efficiencies attained thus far incorporated advances in material refinement, sophisticated cell design, state of the art fabrication technologies, and more importantly a relatively good understanding of the complicated and intertwined physics of charge carrier generation, recombination, and transport. However, for making new generation of high efficiency solar cells, new physics and technology paradigms have to be discovered. Current barriers to high conversion efficiencies are due to current understanding of the physics of photoelectric effect and related phenomena. Breaking those barriers, which would impact photovoltaic technologies, needs refinement of the physics of photoelectric effect with consideration of new materials and new device designs. For instance, development of “ideal” third generation solar cells requires understanding of the early stage of light-matter interaction mechanisms that occur at the nanoscale domains and the related quantum effects. Actually, the improved understanding of these phenomena is repositioning the used linear photoelectric effect occurring in homogenous and continuous planar shallow structure to one that occurs in a volumic

Broadband light-concentration with near-surface distribution by silver capped silicon nanowire for high-performance solar cells

My research projects are focused on application of photonics, optics and micro- fabrication technology in energy related fields. Photonic crystal fabrication research has the potential to help us generate and use light more efficiently. In order to fabricate active 3D woodpile photonic structure devices, a woodpile template is needed to enable the crystal growth process. We developed a silica woodpile template fabrication process based on two polymer transfer molding technique. A silica woodpile template is demonstrated to work with temperature up to 900 C. It provides a more economical way to explore making better 3D active woodpile photonic devices like 3D photonic light emitting diodes (LED). Optical research on solar cell testing has the potential to make our energy generation more e cient and greener. PL imaging and LBIC mapping are used to measure CdTe solar cells with different back contacts. A strong correlation between PL image defects and LBIC map defects is observed. This opens up potential application for PL imaging in fast solar cell inspection. 2D laser IV scan shows its usage in 2D parameter mapping. We show its ability to generate important information about solar cell performance locally around PL image defects.

Photonic devices such as solar cells and photodetectors that produce electricity play a vital role in our daily life for applications such as fibre optic communication systems, process control, and also in defence related applications. Today, two-dimensional perovskites that belong to the class of emerging materials show promising energy applications. 2D perovskites have been investigated for their exceptional properties such as high optical absorption coefficients, structural diversity and tuneable bandgaps which allow their application as active light absorbing materials to develop solar cells and photodetectors. Carbon-based nanomaterials have also found applications as transparent electrodes, charge acceptors and photosensitive layers in solar cells and photodetectors due to properties such as excellent electrical conductivity, high optical transparency, high surface area and remarkable mechanical strength. There has been growing interest in research on devices using these materials to improve their feasibility, ease of production and performance. With the growing urgency of switching to alternate sources of energy and increasing demands for highly accurate and fast sensors, the development and application of such novel materials are essential. Hence, the current state of understanding of these materials and their applications in the field of solar cells and photodetectors are summarized in this review article.

Current–voltage characteristics of electrovoltaic and electrophotovoltaic cells

Applications of functionalized transition metal complexes in photonic and optoelectronic devices

Dielectric colloidal nanospheres (NSs) are promising candidates for light management in photonic devices such as solar cells (SCs). NS arrays can direct the broad incident solar radiation into a set of tighter foci, at which light intensity becomes considerably concentrated, enabling higher photovoltaic conversion efficiency. Furthermore, the NS arrays acting as an effective medium on the SC surface can reduce reflectance and facilitate improved forward scattering. Therefore, uniform arrays of NSs located on top of the SC can behave as antireflection coatings or as microlenses, which can be regarded as a surface distributed light concentrator within the framework of concentrated photovoltaics. Fabrication of NS‐based light‐trapping structures is low‐cost and less complicated than common alternatives such as vacuum evaporated multilayer antireflection coatings. In this work, experimental demonstration and computational confirmation on the shape adjustment of such NS structures for improved light harvesting and efficiency enhancement in Si SCs are studied. The light conversion efficiency of Si solar cells is shown to improve by more than 27% with shape adjustment of NS arrays.

The development of the physical current source with enhanced efficiency based on photoelectric effect is discusses in this article. This source intended for direct conversion of light energy into electricity by modified silicon elements. The 10% efficiency of the silicon solar cell was accepted as basic specifications to assess the efficiency of the developed model. The rationale for the selected materials and structures as well as description of the main stages of manufacturing technology and processing of solar cells (SC) were made.

Advancements in micro/nanofabrication have enabled the realization of practical micro/nanoscale photonic devices such as absorbers, solar cells, metalenses, and metaholograms. Although the performance of these photonic devices has been improved by enhancing the design flexibility of structural materials through advanced fabrication methods, achieving large-area and high-throughput fabrication of tiny structural materials remains a challenge. In this aspect, various technologies have been investigated for realizing the mass production of practical devices consisting of micro/nanostructural materials. This review describes the recent advancements in soft lithography, colloidal self-assembly, and block copolymer self-assembly, which are promising methods suitable for commercialization of photonic applications. In addition, we introduce low-cost and large-scale techniques realizing micro/nano devices with specific examples such as display technology and sensors. The inferences presented in this review are expected to function as a guide for promising methods of accelerating the mass production of various sub-wavelength-scale photonic devices.

We report here electrical properties of low-temperature-stacked electrodes for large-area flexible photonic devices, based on single-crystalline InP nanomembrane (NM) transfer and stacking processes. Au, Al and ITO electrodes were investigated. An excellent ohmic contact was demonstrated on the stacked InP NM–ITO electrode, with a measured contact resistivity of 0.45 Ω cm2. Two types of flexible InP solar cells were also fabricated and characterized, based on the stacked InP NM–ITO and InP NM–Al contacts, respectively. The efficiency of solar cells with ITO as back contact is five times higher than that with Al as back contact. Such low-temperature energy-efficient NM transfer and electrode-stacking techniques can be applied to a wide range of flexible thin film photonic devices.