GaAs-based nanoneedle light emitting diode and avalanche photodiode monolithically integrated on a silicon substrate

Monolithic integration of III-V compound semiconductor devices with silicon CMOS integrated circuits has been hindered by large lattice mismatches and incompatible processing due to high III-V epitaxy temperatures. We report the first GaAs-based avalanche photodiodes (APDs) and light emitting diodes, directly grown on silicon at a very low, CMOS-compatible temperature and fabricated using conventional microfabrication techniques. The APDs exhibit an extraordinarily large multiplication factor at low voltage resulting from the unique needle shape and growth mode.     

Recent progress on cooled avalanche photodiodes for single photon detection

Abstract

Recent results on the properties of cooled avalanche photodiodes for single photon detection are presented. Results from Hamamatsu silicon photodiodes, originally developed as radiation-hard photodetectors for high energy physics experiments, are extremely encouraging. Gains of approximately 10,000 can be achieved with the APD operating in proportional mode. Together with a low noise amplifier they allow photon counting with extremely high efficiency and very low noise making cold APDs almost ideal single photon detectors. Operation of APDs in Geiger mode is also reported, together with measurements of detection efficiency and noise as function of operating voltage. Prospects and hopes for future work are briefly summarized.     

Combinatorial Chance

This paper considers the maximum likelihood estimator (m.l.e.) of the scale parameter of the exponential distribution in a life-testing situation, where the stopping rule is a prestated time. The life-test is examined periodically and the number of items that have failed since the previous inspection are counted. Approximations to the m.l.e. are considered along with their properties.     

Carbon nanotube based photocathodes

This paper describes a novel photocathode which is an array of vertically aligned multi-walled carbon nanotubes (MWCNTs), each MWCNT being associated with one p-i-n photodiode. Unlike conventional photocathodes, the functions of photon-electron conversion and subsequent electron emission are physically separated. Photon-electron conversion is achieved with p-i-n photodiodes and the electron emission occurs from the MWCNTs. The current modulation is highly efficient as it uses an optically controlled reconfiguration of the electric field at the MWCNT locations. Such devices are compatible with high frequency and very large bandwidth operation and could lead to their application in compact, light and efficient microwave amplifiers for satellite telecommunication. To demonstrate this new photocathode concept, we have fabricated the first carbon nanotube based photocathode using silicon p-i-n photodiodes and MWCNT bunches. Using a green laser, this photocathode delivers 0.5?mA with an internal quantum efficiency of 10% and an I(ON)/I(OFF) ratio of 30.     

Accelerated Degradation Tests: Modeling and Analysis

High reliability systems generally require individual system components having extremely high reliability over long periods of time. Short product development times require reliability tests to be conducted with severe time constraints. Frequently few or no failures occur during such tests, even with acceleration. Thus, it is difficult to assess reliability with traditional life tests that record only failure times. For some components, degradation measures can be taken over time. A relationship between component failure and amount of degradation makes it possible to use degradation models and data to make inferences and predictions about a failure-time distribution. This article describes degradation reliability models that correspond to physical-failure mechanisms. We explain the connection between degradation reliability models and failure-time reliability models. Acceleration is modeled by having an acceleration model that describes the effect that temperature (or another accelerating variable) has on the rate of a failure-causing chemical reaction. Approximate maximum likelihood estimation is used to estimate model parameters from the underlying mixed-effects nonlinear regression model. Simulation-based methods are used to compute confidence intervals for quantities of interest (e.g., failure probabilities). Finally we use a numerical example to compare the results of accelerated degradation analysis and traditional accelerated life-test failure-time analysis.     

Improved distributed-index planar microlens and its application to 2-D lightwave components

A recent improvement of a 2-D array of distributed-index (DI) planar microlenses is presented to demonstrate a 2-D integrated optical component using a planar microlens array. These components are made by stacking planar microlens arrays and other planar optical devices. The improved planar microlens has f = 2.0 mm, a N.A. = 0.23, and its spherical aberration is very small. A fiber coupler is demonstrated. From a preliminary experiment, it is shown that the coupling loss of each channel is <0.5 dB for coupling 50-micron core DI fibers.     

Hybrid Light Emitters and UV Solar-Blind Avalanche Photodiodes based on III-Nitride Semiconductors

In the last two decades, remarkable progress has been achieved in the field of optoelectronic devices based on III-nitride semiconductors. In terms of photonics applications in the visible–UV spectral range, III-nitrides are one of the most promising materials. For instance, emerging gallium nitride (GaN)-based micro-light-emitting diode (LED) technology for high-resolution display, and UV photo-detection for environmental monitoring, health, and medical applications. In this work, hybrid micro/nano-LEDs with integration of II–VI quantum dots by means of lithography and nano-imprinting patterning techniques are demonstrated, and high-performance red/green/blue and white emissions are achieved. Consequently, plasmonic nanolasers are designed and fabricated using a metal-oxide-semiconductor structure, where strong surface plasmon polariton coupling leads to the efficient lasing with a low excitation threshold from the visible to UV tunable spectral range. Furthermore, performance-improved AlGaN UV solar-blind avalanche photodiodes (APDs) with a separate absorption and multiplication structure by polarization engineering are reported. These APDs deliver a record-high avalanche gain of up to 1.6 × 10⁵. These newest advances in nano/micro-LEDs, nanolasers, and APDs can shed light on the emerging capabilities of III-nitride in cutting-edge applications.     

Numerical Modeling of Silicon Photodiodes for High-Accuracy Applications Part II. Interpreting Oxide-Bias Experiments

The semiconductor device modeling program PC-1D and the programs that support its use in high-accuracy modeling of photodiodes, all of which were described in Part I of this series of papers, are used to simulate oxide-bias self-calibration experiments on three different types of silicon photodiodes. It is shown that these simulations can be used to determine photodiode characteristics, including the internal quantum efficiency for the different types of photodiodes. In the latter case, the simulations provide more accurate values than can be determined by using the conventional data reduction procedure, and an uncertainty estimate can be derived. Finally, it is shown that 0.9997 ± 0.0003 is a nominal value for the internal quantum efficiency of one type of photodiode over the 440 to 460 nm spectral region.     

Temperature–humidity induced mechanisms in plastic encapsulated bipolar transistors

In this article the disadvantages of well-known models for temperature–humidity induced failure mechanisms in plastic encapsulated microelectronic devices are shown. It is necessary to restrict the validity of these models. The advantage of bipolar transistors is that the failure mechanisms can be separated very easily. The most significant properties of polymers, plastication and glass transition, and also the diffusion of moisture will be described. The hydrolysis of chlorides is considered with respect to processes of polymeric physics and it is shown that chlorides form electrolytic distances and etchant inside the transistors. In this case the microelectronic devices change their electric characteristics and sometimes the electrical connection is interrupted. The model shows that the aggressiveness of the resin is affected by temperature and humidity and also how this aggressiveness affects the transistor. This model combines the mechanisms in the resin with the reactions of the devices. It provides a good basis for improving the reliability of microelectronic devices and for designing proper reliability tests.     

Avalanche photodiodes as large dynamic range detectors for synchrotron radiation

We investigated silicon-based avalanche photodiodes (APDs) as X-ray detectors in terms of their linearity, maximum counting rates, and dynamic range with 8.4 keV synchrotron radiation. Measurements resulted in counting rates that extend from the APD's noise level of 10⁻² Hz to saturation counting rates in excess of 10⁸ Hz. In addition, by monitoring the APD's noise level and photon counting efficiency between synchrotron bursts, we demonstrate nine orders of magnitude dynamic range.     

Reliability of plastic-encapsulated logic circuits

Families of plastic-encapsulated logic circuits have been subjected to a qualification procedure. The aim was to qualify them for use in telecommunication equipment in a central office environment. The qualification was based on a large number of reliability tests performed by the Ericsson failure analysis laboratory and by the vendors themselves. Reliability monitoring data from the testing of more than 150,000 devices during the period 1984 to 1985 have been analysed. Life tests, such as ‘high temperature operating life’, ‘high humidity operating life’, and temperature cycling have been performed. A comparison between life-test data and field data from telephone exchanges in service has also been made. An average activation energy of 0.5 eV has been shown to be useful in such a comparison for the best LS vendors and 0.3 eV for the best HCMOS vendors.     

Stability of interfaces in pseudomorphic ingaas hemts

Considerable progress is now reported on pseudomorphic InGaAs high mobility transistors (PM. HEMTs). However, structures which exhibit the best performances are thermodynamically metastable. The stabilities of commercially available devices have been studied. Investigations of both GaAs InGaAs and AlGaAs/InGaAs interface vicinities have been performed through deep level characterizations. Life-testing experiments have then been carried out in order to assess the stability of the InGaAs buried strained layer and related interfaces during operation. Deep level studies together with electrical parameter measurements indicate that interfaces of InGaAs strained quantum well HEMTs do not induce particular degradations after 3000 hours into biased ageing tests.     

Semiconducting glass design for device applications

A method is presented by which stable amorphous semiconductors can be chosen for switching device applications. This method is based on the empirical relationship observed between the glass transition temperature, the band gap and the mean coordination number of covalent amorphous semiconductors. In particular, it is shown that tetrahedrally coordinated glasses with band gaps in the range 0.6–1.2 eV are excellent candidates for high reliability materials. One such material, a-CdAs₂, was studied in some detail and was found to be very stable and very easy to fabricate in thin film form. Both negative resistance and threshold switching devices were successfully fabricated with this material, and preliminary results from accelerated life testing are promising.     

Factorial Experiments in Life Testing

This paper discusses procedures for analyzing factorial experiments, where the experiment deals with the life testing of components or equipment. These procedures assume an underlying general distribution of “times-to-failure”, of which the exponential, Weibull, and extreme value distributions are special cases. Statistical tests and confidence procedures are outlined, and an example illustrating the procedure for life-test results of glass capacitors is included. Small sample approximations, which are adequate for practical applications, are given for the proposed procedures. This is shown empirically by generating thousands of life-test experiments on an electronic computer. An empirical sampling investigation is given of the robustness of the proposed procedures. From the sampling results, it is concluded that these techniques are sensitive (non-robust) to departures from the original assumptions on the probability distribution of failure-times. An investigation is also given of a transformation which appears to give robust results. These same techniques carry over exactly to the situation where one is analyzing an array of variance estimates from an underlying normal population.     

Homogenous concept for the coupling of active and passive single-mode devices by utilizing planar gradient-index lenses and silicon-V grooves

A new concept for a common interface between passive and active single-mode devices is proposed. The submicrometer alignment accuracy necessary for efficient coupling of single-mode devices is extended to the range of some 10 mum by beam expansion with planar gradient-index microlenses; the increased angular sensitivity is satisfied by the use of planar surfaces. The imaging system is used off axis, resulting in a suppression of backreflections in the range >60 dB. Of many possible variations of components (fibers, waveguides, optoelectronic integrated circuits, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodiodes), the coupling of fibers and waveguides is examined in detail. Expected coupling efficiency and sensitivity to lateral misalignment are calculated by use of a modified beam-propagation method. In this way, the overall performance of the connector can be compared with existing connector concepts, and the feasibility of the concept is proven. Experimental results for the fiber-fiber connector are given.     

Remote Sensors with Self‐Test: New Opportunities to Improve the Performance of Physical Transducers

When addressing the question on how to operate sensors in a remote environment, i.e., in non‐accessible places, the issue of reliability becomes of extreme importance. Especially in the case where miniaturisation is essential, often the physical geometries become that small that the sensor performance degrades to yield only very weak signal levels. Matching circuits are an essential element. Monitoring physical quantities from a remote and difficult to access location requires high standards for the sensors and their circuits involved: it is essential that the data remains reliable at all times. This is a hard requirement, and many sensors used in such applications cannot cope with such severe specifications, as there are: low drift, high stability in time, immunity to cross sensitivies, etc. This paper focuses on a double solution: first by adding circuitry improving the intelligence of the entire sensor system. Secondly, it is shown how the sensor design in itself can be modified to improve the interface circuit performance. An essential element is the addition of built‐in self‐test features to verify the correct operation of the sensor at any given moment in time. Crucial in these novel developments is that the measurand itself is used to verify the operation of the sensor, and not a related actuation as is done in many existing devices.     

Macroscopic assembly of indefinitely long and parallel nanowires into large area photodetection circuitry

Integration of nanowires into functional devices with high yields and good reliability turned out to be a lot more challenging and proved to be a critical issue obstructing the wide application of nanowire-based devices and exploitation of their technical promises. Here we demonstrate a relatively easy macrofabrication of a nanowire-based imaging circuitry using a recently developed nanofabrication technique. Extremely long and polymer encapsulated semiconducting nanowire arrays, mass-produced using the iterative thermal drawing, facilitate the integration process; we manually aligned the fibers containing selenium nanowires over a lithographically defined circuitry. Controlled etching of the encapsulating polymer revealed a monolayer of nanowires aligned over an area of 1 cm(2) containing a 10 × 10 pixel array. Each light-sensitive pixel is formed by the contacting hundreds of parallel photoconductive nanowires between two electrodes. Using the pixel array, alphabetic characters were identified by the circuitry to demonstrate its imaging capacity. This new approach makes it possible to devise extremely large nanowire devices on planar, flexible, or curved substrates with diverse functionalities such as thermal sensors, phase change memory, and artificial skin.     

High‐Performance Photovoltaic Detector Based on MoTe2/MoS2 Van der Waals Heterostructure

Van der Waals heterostructures based on 2D layered materials have received wide attention for their multiple applications in optoelectronic devices, such as solar cells, light‐emitting devices, and photodiodes. In this work, high‐performance photovoltaic photodetectors based on MoTe₂/MoS₂ vertical heterojunctions are demonstrated by exfoliating‐restacking approach. The fundamental electric properties and band structures of the junction are revealed and analyzed. It is shown that this kind of photodetectors can operate under zero bias with high on/off ratio (>10⁵) and ultralow dark current (≈3 pA). Moreover, a fast response time of 60 µs and high photoresponsivity of 46 mA W^?1 are also attained at room temperature. The junctions based on 2D materials are expected to constitute the ultimate functional elements of nanoscale electronic and optoelectronic applications.     

Organic Microcavity Photodiodes

The interaction of light and matter lies at the heart of the principle of optoelectronic devices. By tuning the strength of the electric field component of the light wave, one can gain control over this interaction. A simple way of achieving this is by employing microcavities, which are one‐dimensional photonic structures. These give rise to an effective quantization of the light field in one direction. The largest enhancements in the strength of light–matter coupling are achieved for cavities with dimensions on the order of the effective wavelength of light. As organic materials have the very large oscillator strengths required for light–matter coupling, as well as excellent thin film forming properties, they are ideal materials with which to exploit tunable electron–photon coupling. We demonstrate the influence of the optical field strength in organic microcavity photodiodes. Besides allowing tunability of the response spectrum by varying the effective resonator thickness, a large increase in the photocurrent sensitivity is observed below the absorption threshold of the optically active material. The microcavity induced field enhancement plays a particularly important role under two‐photon excitation. In this case we observe a 500‐fold increase in the photocurrent response with respect to a non‐cavity device. This opens up a range of applications for organic microcavity photodiodes as nonlinear detector elements.