Solid state image sensor research Final technical report

Fifty-element linear arrays of InAs photodiode

High-temperature optically activated GaAs power switching for aircraft digital electronic control

Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas

Infrared receivers for low background astronomy: Incoherent detectors and coherent devices from one micrometer to one millimeter

The status of incoherent detectors and coherent receivers over the infrared wavelength range from one micrometer to one millimeter is described. General principles of infrared receivers are included, and photon detectors, bolometers, coherent receivers, and important supporting technologies are discussed, with emphasis on their suitability for low background astronomical applications. Broad recommendations are presented and specific opportunities are identified for development of improved devices

Light Generation and Harvesting in a Van der Waals Heterostructure

Two-dimensional (2D) materials are a new type of materials under intense study because of their interesting physical properties and wide range of potential applications from nanoelectronics to sensing and photonics. Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have been proposed as promising channel materials for field-effect transistors (FETs). Their high mechanical flexibility, stability and quality coupled with potentially inexpensive production methods offer potential advantages compared to organic and crystalline bulk semiconductors. Due to quantum mechanical confinement, the band gap in monolayer MoS2 is direct in nature, leading to a strong interaction with light that can be exploited for building phototransistors and ultrasensitive photodetectors. Here, we report on the realization of light-emitting diodes based on vertical heterojunctions composed of n-type monolayer MoS2 and p-type silicon. Careful interface engineering allows us to realize diodes showing rectification and light emission from the entire surface of the heterojunction. Electroluminescence spectra show clear signs of direct excitons related to the optical transitions between the conduction and valence bands. Our pn diodes can also operate as solar cells, with typical external quantum efficiency exceeding 4%. Our work opens up the way to more sophisticated optoelectronic devices such as lasers and heterostructure solar cells based on hybrids of two-dimensional (2D) semiconductors and silicon.Comment: Submitted versio

Moderate temperature detector development

The development of (Hg, Cd)Te detectors for 8 to 12 micrometer wavelength regions capable of achieving significantly improved sensitivity at noncryogenic temperatures is discussed

State-of-the-art all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths

Silicon-based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics. In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption - due to its bandgap of 1.12 eV. Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 1.1 μm, in recent years tremendous advances have been made in the field of all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths. By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well-established technologies, and are opening new and intriguing perspectives. In this paper, a review of the state-of-the-art is presented. Devices based on defect-mediated absorption, two-photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared

Performance and Degradation Analysis of Operating PV Systems

The environmental concerns together with the decrease in technology cost lead the solar market to growth rapidly along the last decade. The photovoltaic (PV) systems are one of the solar energy alternatives and the silicon solar cells are currently the most widespread technology. Photovoltaic (PV) modules are considered the most reliable component of a photovoltaic system. The reliability and lifetime depends on the modules energy conversion performance and degradation modes. The analysis of monitoring data give insights about the PV system performance along its service time. The comparison between this data and mathematical models configure a way to predict the futures and new PV installations performance. The goal of this study is to understand the PV systems performance and degradation along its lifetime. A mathematical model was employed to predict the power output of a real, relatively new operating PV system with respect to environmental parameters temperature, irradiance and cloud coverage. The model used is based on one diode ideality factor and takes into account the parasitic series resistance. The results have been compared with the actual PV output data collected for the year 2014 and show good correlation. As the model predicts the system power output assuming the system in new conditions, the deviation in performance of the real data in comparison to the modeling results need to be further investigated for systems in service for longer time. For this propose, the study presents a condensed review of various causes of degradation in silicon PV modules and techniques to observe and investigate these degradation mechanisms. Major effects on output performance exhibit increase in observed ideality factor n2 and recombination current J02 primarily caused by decrease in minority carrier lifetime, shunts and increase in series resistance. The study further, investigates the governing degradation modes on a ten years old PV crystalline silicon module operating under the similar weather conditions and the resultant effect on its performance. IR imaging for hot spot detection has been employed in examining on this PV module that shows localized damaged regions. PV I-V characteristics reveal some cells performing poorly in the panel due to these degradations. This work may lead to future work on developing models that include dynamic changes in cell/module parameters and techniques to mitigate / inspect / monitor degradation in real time

Development of a unique laboratory standard indium gallium arsenide detector for the 500 to 1700 micron spectral region, phase 2

In the course of this work, 5 mm diameter InGaAs pin detectors were produced which met or exceeded all of the goals of the program. The best results achieved were: shunt resistance of over 300 K ohms; rise time of less than 300 ns; contact resistance of less than 20 ohms; quantum efficiency of over 50 percent in the 0.5 to 1.7 micron range; and devices were maintained and operated at 125 C without deterioration for over 100 hours. In order to achieve the goals of this program, several major technological advances were realized, among them: successful design, construction and operation of a hydride VPE reactor capable of growing epitaxial layers on 2 inch diameter InP substrates with a capacity of over 8 wafers per day; wafer processing was upgraded to handle 2 inch wafers; a double layer Si3N4/SiO2 antireflection coating which enhances response over the 0.5 to 1.7 micron range was developed; a method for anisotropic, precisely controlled CH4/H2 plasma etching for enhancement of response at short wavelengths was developed; and electronic and optical testing methods were developed to allow full characterization of detectors with size and spectral response characteristics. On the basis of the work and results achieved in this program, it is concluded that large size, high shunt resistance, high quantum efficiency InGaAs pin detectors are not only feasible but also manufacturable on industrial scale. This device spans a significant portion of visible and near infrared spectral range and it will allow a single detector to be used for the 0.5 to 1.7 micron spectral region, rather than the presently used silicon (for 0.5 to 1.1 microns) and germanium (0.8 to 1.7 microns)

Gated lateral silicon p-i-n junction photodiodes

Research in silicon photonics has recently seen a significant push to develop complete silicon-based optical components for optical communications. Silicon has shown its potential to overcome the bandwidth limitations of microprocessor interconnect, whereas, the silicon platform has already displayed the benefits of low manufacturing costs and CMOS compatibility. The work on “gated lateral silicon p-i-n junction photodiodes” has demonstrated the silicon potential, to detect optical radiations, compatibility to standard CMOS process flow and tuneable spectral response. The lateral structure of gated p-i-n junction photodiodes contributes to high responsivity to short wavelength radiations in these single and dual gate devices. The final objective of this work was to develop high responsivity, CMOS-compatible silicon photodiodes, where the spectral response can be modulated. The lateral p-i-n junction architecture led to high responsivity values, whereas, the MOS gate structure became the basis for tuneable spectral response. The MOS gate structure, made the devices appear as a transistor to the surrounding circuitry and the gate structure in dual gate devices can be used to modulate the spectral response of the device. Single gate devices showed higher responsivity values and comparatively high blue and ultraviolet (UV) response as compared to conventional photodiodes. Surface depletion region in these devices is utilized by placing a MOS gate structure and by patterning an integrated metal grating to detect polarized light. Single and dual gate devices with two variations were fabricated to characterise the device response. Novel lateral architecture of p-i-n junction photodiodes provides a surface depletion region. It is generally anticipated that photodetectors with surface depletion region might produce higher noise. In these devices the surface depletion region has a lateral continuation of gate dielectric which acts as a passivation layer and thus considerably reduced the noise. Physical device modelling studies were performed to verify the experimentally obtained results, which are provided in the relevant measurement chapters. In these devices the speed of operation is a compromise over the high responsivity, CMOS compatibility and tuneable spectral response