Associated Factors of Worrying About Loneliness Before Death.

Human beings' welfare is closely related to their social relationships, and lack of that relationship could result in social isolation and loneliness. Various types of loneliness have been discussed in the literature, but a sense of loneliness before death has received no attention. Thus, this study is conducted to better understand the mechanism and nature of that type of loneliness. The response of this study was "Do you worry that you may be alone when you are dying?". After highlighting the most important features, to examine the true associations between various factors and a sense of loneliness, the pairwise interactions across various variables were considered. It was found, for instance, while attending religious service, having higher subjective life condition, and being older are negatively associated with the response, belief that success depends on God and higher income are positively associated with that feeling. Also, while married people are less worried about loneliness before death, this interacts with a myriad of factors. Similarly, positive associations were found across responses and a higher concern that those close with us won't be with us, or those who we care about might not remember us after death.

Students' negative emotions and their rational and irrational behaviors during COVID-19 outbreak.

The pandemic has posed an intense threat to the mental health of younger adults. Despite significant efforts in studying various aspects of COVID-19, there is a dearth of evidence on how negative emotions are associated with behaviors. A comparison across associated factors to different negative emotions by means of a unified model is especially missing from the literature. This study was conducted by using the results of a survey conducted across 2,534 students enrolled in 7 states in the US. Various feelings such as sad, irritable, stress and guilt were analyzed in a unified model by means of seemingly unrelated regression (SUR). Questions were asked related to rationally limiting the spread of virus, and questions related to behaviors that seem to be extreme. Irrational behaviors, such as limiting exercise at home due to COVID-19 could be due to experiencing negative emotions, which distort the meaning of events for the students. That behavior, for instance, was found to be positively associated with various negative feelings. In addition, the results highlighted significant differences across emotions in terms of demographic characteristics such as gender and age, and various precautionary actions that students take, such as limiting outdoor activities or limiting social gathering. For instance, it was highlighted while avoiding a large group of people, in spite of its importance in curbing the spread of virus, is negatively associated with various negative emotions, taking a possible nonconsequential precaution of completely limiting all people outside the immediate family result in a higher level of negative emotions. Also, it was found that having a higher body mass index (BMI), self-rated worse health conditions, and limiting outdoor activities have detrimental effects on the mental health of students.

Mid-wavelength infrared avalanche photodetector with AlAsSb/GaSb superlattice.

In this work, a mid-wavelength infrared separate absorption and multiplication avalanche photodiode (SAM-APD) with 100% cut-off wavelength of ~ 5.0 µm at 200 K grown by molecular beam epitaxy was demonstrated. The InAsSb-based SAM-APD device was designed to have electron dominated avalanche mechanism via the band structure engineered multi-quantum well structure based on AlAsSb/GaSb H-structure superlattice and InAsSb material in the multiplication region. The device exhibits a maximum multiplication gain of 29 at 200 K under -14.7 bias voltage. The maximum multiplication gain value for the MWIR SAM-APD increases from 29 at 200 K to 121 at 150 K. The electron and hole impact ionization coefficients were derived and the large difference between their value was observed. The carrier ionization ratio for the MWIR SAM-APD device was calculated to be ~ 0.097 at 200 K.

Band-structure-engineered high-gain LWIR photodetector based on a type-II superlattice.

The LWIR and longer wavelength regions are of particular interest for new developments and new approaches to realizing long-wavelength infrared (LWIR) photodetectors with high detectivity and high responsivity. These photodetectors are highly desirable for applications such as infrared earth science and astronomy, remote sensing, optical communication, and thermal and medical imaging. Here, we report the design, growth, and characterization of a high-gain band-structure-engineered LWIR heterojunction phototransistor based on type-II superlattices. The 1/e cut-off wavelength of the device is 8.0 µm. At 77 K, unity optical gain occurs at a 90 mV applied bias with a dark current density of 3.2 × 10-7 A/cm2. The optical gain of the device at 77 K saturates at a value of 276 at an applied bias of 220 mV. This saturation corresponds to a responsivity of 1284 A/W and a specific detectivity of 2.34 × 1013 cm Hz1/2/W at a peak detection wavelength of ~6.8 µm. The type-II superlattice-based high-gain LWIR device shows the possibility of designing the high-performance gain-based LWIR photodetectors by implementing the band structure engineering approach.

Type-II superlattices base visible/extended short-wavelength infrared photodetectors with a bandstructure-engineered photo-generated carrier extractor.

Visible/extended short-wavelength infrared photodetectors with a bandstructure-engineered photo-generated carrier extractor based on type-II InAs/AlSb/GaSb superlattices have been demonstrated. The photodetectors are designed to have a 100% cut-off wavelength of ~2.4 µm at 300K, with sensitivity down to visible wavelengths. The photodetectors exhibit room-temperature (300K) peak responsivity of 0.6 A/W at ~1.7 µm, corresponding to a quantum efficiency of 43% at zero bias under front-side illumination, without any anti-reflection coating where the visible cut-on wavelength of the devices is <0.5 µm. With a dark current density of 5.3 × 10-4 A/cm2 under -20 mV applied bias at 300K, the photodetectors exhibit a specific detectivity of 4.72 × 1010 cm·Hz1/2/W. At 150K, the photodetectors exhibit a dark current density of 1.8 × 10-10 A/cm2 and a quantum efficiency of 40%, resulting in a detectivity of 5.56 × 1013 cm·Hz1/2/W.

nBn extended short-wavelength infrared focal plane array.

An extended short-wavelength nBn InAs/GaSb/AlSb type-II superlattice-based infrared focal plane array imager was demonstrated. A newly developed InAs0.10Sb0.90/GaSb superlattice design was used as the large-bandgap electron barrier in this photodetector. The large band gap electron-barrier design in this nBn photodetector architecture leads to the device having lower dark current densities. A new bi-layer etch-stop scheme using a combination of InAs0.91Sb0.09 bulk and AlAs0.1Sb0.9/GaSb superlattice layers was introduced to allow complete substrate removal and a shorter wavelength cut-on. Test pixels exhibit 100% cutoff wavelengths of ∼2.30 and ∼2.48 µm at 150 and 300 K, respectively. The devices achieve saturated quantum efficiency values of 59.7% and 63.8% at 150 and 300 K, respectively, under backside illumination and without any antireflection coating. At 150 K, photodetectors exhibit dark current density of 8.75×10-8 A/cm2 under -400 mV applied bias, providing specific detectivity of 2.82×1012 cm·Hz1/2/W at 1.78 µm. At 300 K, the dark current density reaches 4.75×10-2 A/cm2 under -200 mV bias, providing a specific detectivity of 8.55×109 cm·Hz1/2/W 1.78 µm.

Type-II superlattice-based extended short-wavelength infrared focal plane array with an AlAsSb/GaSb superlattice etch-stop layer to allow near-visible light detection.

A versatile infrared imager capable of imaging the near-visible to the extended short-wavelength infrared (e-SWIR) is demonstrated using e-SWIR InAs/GaSb/AlSb type-II superlattice-based photodiodes. A bi-layer etch-stop scheme consisting of bulk InAs0.91Sb0.09 and AlAs0.1Sb0.9/GaSb superlattice layers is introduced for substrate removal from the hybridized back-side illuminated photodetectors. The implementation of this new technique on an e-SWIR focal plane array results in a significant enhancement in the external quantum efficiency (QE) in the 1.8-0.8 µm spectral region, while maintaining a high QE at wavelengths longer than 1.8 µm. Test pixels exhibit 100% cutoff wavelengths of ∼2.1 and ∼2.25 µm at 150 and 300 K, respectively. They achieve saturated QE values of 56% and 68% at 150 and 300 K, respectively, under back-side illumination and without any anti-reflection coating. At 150 K, the photodetectors (27 µm×27 µm area) exhibit a dark current density of 4.7×10-7 A/cm2 under a -50 mV applied bias providing a specific detectivity of 1.77×1012 cm·Hz1/2/W. At 300 K, the dark current density reaches 6.6×10-2 A/cm2 under -50 mV bias, providing a specific detectivity of 5.17×109 cm·Hz1/2/W.

Bias-selectable nBn dual-band long-/very long-wavelength infrared photodetectors based on InAs/InAs1-xSbx/AlAs1-xSbx type-II superlattices.

Type-II superlattices (T2SLs) are a class of artificial semiconductors that have demonstrated themselves as a viable candidate to compete with the state-of-the-art mercury-cadmium-telluride material system in the field of infrared detection and imaging. Within type-II superlattices, InAs/InAs1-xSbx T2SLs have been shown to have a significantly longer minority carrier lifetime. However, demonstration of high-performance dual-band photodetectors based on InAs/InAs1-xSbx T2SLs in the long and very long wavelength infrared (LWIR & VLWIR) regimes remains challenging. We report the demonstration of high-performance bias-selectable dual-band long-wavelength infrared photodetectors based on new InAs/InAs1-xSbx/AlAs1-xSbx type-II superlattice design. Our design uses two different bandgap absorption regions separated by an electron barrier that blocks the transport of majority carriers to reduce the dark current density of the device. As the applied bias is varied, the device exhibits well-defined cut-off wavelengths of either ∼8.7 or ∼12.5 µm at 77 K. This bias-selectable dual-band photodetector is compact, with no moving parts, and will open new opportunities for multi-spectral LWIR and VLWIR imaging and detection.

Impact of scaling base thickness on the performance of heterojunction phototransistors.

In this letter we report the effect of vertical scaling on the optical and electrical performance of mid-wavelength infrared heterojunction phototransistors based on type-II InAs/GaSb/AlSb superlattices. The performance of devices with different base thickness was compared as the base was scaled from 60 down to 40 nm. The overall optical performance shows enhancement in responsively, optical gain, and specific detectivity upon scaling the base width. The saturated responsivity for devices with 40 nm bases reaches 8845 and 9528 A W-1 at 77 and 150 K, respectively, which is almost five times greater than devices with 60 nm bases. The saturated optical gain for devices with 40 nm bases is measured as 2760 at 77 K and 3081 at 150 K. The devices with 40 nm bases also exhibit remarkable enhancement in saturated current gain, with 17690 at 77 K, and 19050 at 150 K.

High performance bias-selectable three-color Short-wave/Mid-wave/Long-wave Infrared Photodetectors based on Type-II InAs/GaSb/AlSb superlattices.

We propose a new approach in device architecture to realize bias-selectable three-color shortwave-midwave-longwave infrared photodetectors based on InAs/GaSb/AlSb type-II superlattices. The effect of conduction band off-set and different doping levels between two absorption layers are employed to control the turn-on voltage for individual channels. The optimization of these parameters leads to a successful separation of operation regimes; we demonstrate experimentally three-color photodiodes without using additional terminal contacts. As the applied bias voltage varies, the photodiodes exhibit sequentially the behavior of three different colors, corresponding to the bandgap of three absorbers. Well defined cut-offs and high quantum efficiency in each channel are achieved. Such all-in-one devices also provide the versatility of working as single or dual-band photodetectors at high operating temperature. With this design, by retaining the simplicity in device fabrication, this demonstration opens the prospect for three-color infrared imaging.

Effect of geometric parameters on the performance of p-type junctionless lateral gate transistors.

This paper examines the impact of two important geometrical parameters, namely the thickness and source/drain extensions on the performance of low doped p-type double lateral gate junctionless transistors (DGJLTs). The three dimensional Technology Computer-Aided Design simulation is implemented to calculate the characteristics of the devices with different thickness and source/drain extension and based on that, the parameters such as threshold voltage, transconductance and resistance in saturation region are analyzed. In addition, simulation results provide a physical explanation for the variation of device characteristics given by the variation of geometric parameters, mainly based on investigation of the electric field components and the carries density variation. It is shown that, the variation of the carrier density is the main factor which affects the characteristics of the device when the device's thickness is varied. However, the electric field is mainly responsible for variation of the characteristics when the source/drain extension is changed.

Gate length variation effect on performance of gate-first self-aligned In0.53Ga0.47As MOSFET.

A multi-gate n-type In0.53Ga0.47As MOSFET is fabricated using gate-first self-aligned method and air-bridge technology. The devices with different gate lengths were fabricated with the Al2O3 oxide layer with the thickness of 8 nm. In this letter, impact of gate length variation on device parameter such as threshold voltage, high and low voltage transconductance, subthreshold swing and off current are investigated at room temperature. Scaling the gate length revealed good enhancement in all investigated parameters but the negative shift in threshold voltage was observed for shorter gate lengths. The high drain current of 1.13 A/mm and maximum extrinsic transconductance of 678 mS/mm with the field effect mobility of 364 cm(2)/Vs are achieved for the gate length and width of 0.2 µm and 30 µm, respectively. The source/drain overlap length for the device is approximately extracted about 51 nm with the leakage current in order of 10(-8) A. The results of RF measurement for cut-off and maximum oscillation frequency for devices with different gate lengths are compared.

Impact of parameter variation in fabrication of nanostructure by atomic force microscopy nanolithography.

In this letter, we investigate the fabrication of Silicon nanostructure patterned on lightly doped (10(15) cm(-3)) p-type silicon-on-insulator by atomic force microscope nanolithography technique. The local anodic oxidation followed by two wet etching steps, potassium hydroxide etching for silicon removal and hydrofluoric etching for oxide removal, are implemented to reach the structures. The impact of contributing parameters in oxidation such as tip materials, applying voltage on the tip, relative humidity and exposure time are studied. The effect of the etchant concentration (10% to 30% wt) of potassium hydroxide and its mixture with isopropyl alcohol (10%vol. IPA ) at different temperatures on silicon surface are expressed. For different KOH concentrations, the effect of etching with the IPA admixture and the effect of the immersing time in the etching process on the structure are investigated. The etching processes are accurately optimized by 30%wt. KOH +10%vol. IPA in appropriate time, temperature, and humidity.

Electrical property comparison and charge transmission in p-type double gate and single gate junctionless accumulation transistor fabricated by AFM nanolithography.

The junctionless nanowire transistor is a promising alternative for a new generation of nanotransistors. In this letter the atomic force microscopy nanolithography with two wet etching processes was implemented to fabricate simple structures as double gate and single gate junctionless silicon nanowire transistor on low doped p-type silicon-on-insulator wafer. The etching process was developed and optimized in the present work compared to our previous works. The output, transfer characteristics and drain conductance of both structures were compared. The trend for both devices found to be the same but differences in subthreshold swing, 'on/off' ratio, and threshold voltage were observed. The devices are 'on' state when performing as the pinch off devices. The positive gate voltage shows pinch off effect, while the negative gate voltage was unable to make a significant effect on drain current. The charge transmission in devices is also investigated in simple model according to a junctionless transistor principal.

Preparation, characterization and thermal degradation of polyimide (4-APS/BTDA)/SiO(2) composite films.

Polyimide/SiO(2) composite films were prepared from tetraethoxysilane (TEOS) and poly(amic acid) (PAA) based on aromatic diamine (4-aminophenyl sulfone) (4-APS) and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride) (BTDA) via a sol-gel process in N-methyl-2-pyrrolidinone (NMP). The prepared polyimide/SiO(2) composite films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA) and the formation of SiO(2) particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO(2) particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO(2) composite films were investigated using TGA in N(2) atmosphere. The activation energy of the solid-state process was calculated using Flynn-Wall-Ozawa's method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions.

Pinch-off mechanism in double-lateral-gate junctionless transistors fabricated by scanning probe microscope based lithography.

A double-lateral-gate p-type junctionless transistor is fabricated on a low-doped (10(15)) silicon-on-insulator wafer by a lithography technique based on scanning probe microscopy and two steps of wet chemical etching. The experimental transfer characteristics are obtained and compared with the numerical characteristics of the device. The simulation results are used to investigate the pinch-off mechanism, from the flat band to the off state. The study is based on the variation of the carrier density and the electric-field components. The device is a pinch-off transistor, which is normally in the on state and is driven into the off state by the application of a positive gate voltage. We demonstrate that the depletion starts from the bottom corner of the channel facing the gates and expands toward the center and top of the channel. Redistribution of the carriers due to the electric field emanating from the gates creates an electric field perpendicular to the current, toward the bottom of the channel, which provides the electrostatic squeezing of the current.