Thermal interdiffusion in InGaAs/GaAs strained multiple quantum well infrared photodetector

RTA at 850 °C for 5 and 10 s is carried out to study the effect of interdiffusion on the optical and electrical properties of strained InGaAs/GaAs quantum well infrared photodetector. Photoluminescence measurement at 4.5 K shows that no strain relaxation or misfit dislocation formation occurs throughout the annealing process. Absorption and responsivity peak wavelengths are red shifted continuously without appreciable degradation in absorption strength. The normal incident absorption, which is believed to be the result of band-mixing effects induced by the coupling between the conduction and valence and is usually forbidden in conventional polarization selection rule, is preserved after interdiffusion. Responsivity spectra of both 0° and 90° polarization are of compatible amplitude and the shape of the annealed spectra becomes narrower. Dark current of the annealed devices is not very sensitive to temperature variation and is found to be an order of magnitude larger than the as-grown one at 77K.published_or_final_versio

Understanding of self-terminating pulse generation using silicon controlled rectifier and RC load

The article of record as published may be found at http://dx.doi.org/10.1063/1.4940305Recently a silicon controlled rectifier (SCR)-based circuit that generates self-terminating voltage pulses was employed for the detection of light and ionizing radiation in pulse mode. The circuit consisted of a SCR connected in series with a RC load and DC bias. In this paper, we report the investigation of the physics underlying the pulsing mechanism of the SCR-based. It was found that during the switching of SCR, the voltage across the capacitor increased beyond that of the DC bias, thus generating a reverse current in the circuit, which helped to turn the SCR off. The pulsing was found to be sustainable only for a specific range of RC values depending on the SCR’s intrinsic turn-on/off times. The findings of this work will help to design optimum SCR based circuits for pulse mode detection of light and ionizing radiation without external amplification circuitry.The National Consortium for MASINT research (NCMR)Sam BaroneThe National Consortium for MASINT research (NCMR

Impurity-free intermixing of InGaAs/GaAs-strained multiple quantum well infrared photodetectors

Interdiffusion effect has been investigated in highly strained InGaAs/GaAs multiple quantum well (MQW) IR photodetector. Impurity-free interdiffusion techniques was utilized via rapid thermal annealing (RTA) using electron- beam evaporated SiO2 cap layers at temperature 850 degrees C to study the optical and electrical properties of the interdiffused photodetector. Photoluminescence (PL) spectrum is blue shifted and PL linewidth remains almost the same, indicating no strain relaxation and deterioration of the heterostructure quality. Both transverse magnetic and transverse electric IR intersubband transitions are retained and observed after intermixing. The absorption peak wavelength is red shifted continuously from the as grown 10.20 to the interdiffused 10.5 and 11.17 micrometers , respectively, without appreciable degradation in absorption strength for 5 and 10 s annealing. Annealed responsivity spectra of both 0 degrees and 90 degrees polarization are of compatible amplitude and red shifted but with narrower spectra linewidth. Dark current of the annealed devices is found to be an order of magnitude large than the as-grown one at 77K.published_or_final_versio

Electronic phase shift measurement for the determination of acoustic wave DoA using single MeMS biomimetic sensor

The article of record as published may be found at http://dx.doi.org/10.1038/s41598-020-69563-1MeMS acoustic sensors have been developed to mimic the highly-accurate sound-locating system of the Ormia ochracea fly, which detects sound wavelengths much larger than its hearing organ. A typical ormia-based MeMS directional sound sensor possesses two coupled wings that vibrate in response to sound according to a superposition of its two main resonant modes, rocking and bending. Vibrations are transduced into electronic signals by interdigitated comb finger capacitors at each wing'[s end along with a capacitance measuring circuitry. A sensor designed to exhibit resonant modes closely placed in frequency, enhancing their coupling, was operated with a closed cavity behind the wings. Simultaneous and independent measurements of electronic signals generated at each of the single sensor wings were used to determine incident sound direction of arrival (DoA). DoA was found proportional to the phase shift between them and to the difference over the sum of their amplitudes as well. Single sensor phase shift DOA measurement presented a resolution better than 3(degrees) for sound pressure levels of 25 mPa or greater. These results indicate that a single sensor operating in closed- cavity configuration can provide hemispherical unambiguous direction of arrival of sound waves which wavelength is much larger than the sensor size.This work was supported by the Office of Naval Research (ONR) and the Consortium for Robotics and Unmanned Systems Education and Research (CRUSER)

Bio-Inspired MEMS Direction Finding Underwater Acoustic Sensor Operating in Neutral-Buoyant Configuration

For American Physical Society March Meeting 2020, Session on Detectors, Sensors, and TransducersAPS March Meeting 2020MEMS acoustic sensors were developed based on the mechanically coupled auditory structure of the Ormia Ochracea fly in order to enhance underwater directional sound-sensing technologies. MEMS directional acoustic sensors consists of two wings connected by a bridge in the middle. The entire mechanical structure is connected to a substrate using two torsional legs. The mechanical vibrations under sound excitation is transduced to an electrical signal using interdigitated comb finger capacitors attached to the edges of the wings. This presentation covers the design, fabrication, and characterization of Ormia-based MEMS directional acoustic sensor operated underwater as an inertial sensor. The sensors were designed using FE modeling tools and fabricated using commercially available MEMSCap SOIMUMPS processes. Characterization was performed in air and underwater, showing the predicted frequency and directional responses. For underwater operation, the sensors were housed in a near-neutral-buoyant, hermetically sealed enclosure. Results indicate that the MEMS acoustic sensor's microphone characteristics are preserved when operated as accelerometers, and they have a great potential to be used for underwater applications in a neutral-buoyant configuration.GIMSOffice of Naval ResearchGIM

Bi-material terahertz sensors using metamaterial structures

The article of record as published may be found at http://dx.doi.org/10.1364/OE.21.013256In this paper we report on the design, fabrication and characterization of terahertz (THz) bi-material sensors with metamaterial absorbers. MEMS fabrication-friendly SiOx and Al are used to maximize the bimetallic effect and metamaterial absorption at 3.8 THz, the frequency of a quantum cascade laser illumination source. Sensors with different configurations were fabricated and the measured absorption is near 100% and responsivity is around 1.2 degrees which agree well with finite element simulations. The results indicate the potential of using these detectors to fabricate focal plane arrays for real time THz imaging.ONR and NR

Thermal Re-emission Model

Starting from a continuum description, we study the non-equilibrium roughening of a thermal re-emission model for etching in one and two spatial dimensions. Using standard analytical techniques, we map our problem to a generalized version of an earlier non-local KPZ (Kardar-Parisi-Zhang) model. In 2+1 dimensions, the values of the roughness and the dynamic exponents calculated from our theory go like $\alpha \approx z \approx 1$ and in 1+1 dimensions, the exponents resemble the KPZ values for low vapor pressure, supporting experimental results. Interestingly, Galilean invariance is maintained althrough.Comment: 4 pages, minor textual corrections and typos, accepted in Physical Review B (rapid

Fabrication of MEMS Directional Acoustic Sensors for Underwater Operation

The article of record as published may be found at https://doi.org/10.3390/s20051245In this work, microelectromechanical systems (MEMS)-based directional acoustic sensors operating in an underwater environment are explored. The studied sensors consist of a free-standing single wing or two wings pivoted to a substrate. The sensors operate in a narrow frequency band determined by the resonant frequency of the mechanical structure. The electronic readout of the mechanical response is obtained using interdigitated comb finger capacitors attached to the wings. The characteristics of MEMS sensors immersed in silicone oil are simulated using finite element modeling. The performance of the sensors is evaluated both in air and underwater. For underwater testing and operation, the sensors are packaged in a housing containing silicone oil, which was specially developed to present near unity acoustic transmission. The measurements show that the resonant frequency of the sensors obtained in air shifts to a lower frequency when immersed in silicone oil, which is primarily due to the mass loading of the liquid. The peak sensitivity of the MEMS sensors is approximately 6 mV/Pa or −165 dB re 1 V/μPa, and the directional response shows a dipole pattern. The signal-to-noise ratio was found to be about 200 or 23 dB at 1 Pa incident sound pressure. The results show the potential of MEMS sensors to be used in underwater applications for sound source localization

Bulk dynamics for interfacial growth models

We study the influence of the bulk dynamics of a growing cluster of particles on the properties of its interface. First, we define a {\it general bulk growth model} by means of a continuum Master equation for the evolution of the bulk density field. This general model just considers arbitrary addition of particles (though it can be easily generalized to consider substraction) with no other physical restriction. The corresponding Langevin equation for this bulk density field is derived where the influence of the bulk dynamics is explicitly shown. Finally, when it is assumed a well-defined interface for the growing cluster, the Langevin equation for the height field of this interface for some particular bulk dynamics is written. In particular, we obtain the celebrated Kardar-Parisi-Zhang (KPZ) equation. A Monte Carlo simulation illustrates the theoretical results.Comment: 6 pages, 2 figure