We propose a Nanodiamond based Biological Physical Unclonable Function for securing in-vivo and in-vitro biosensing devices connected to Internet-of Things healthcare systems for remote patient monitoring . We take advantage of nontoxic biocompatibility and antibacterial activity of nanodiamond films and cavities that can produce strong pseudo-random electromagnetic responses upon electrical or laser triggering due to the fluorescence coming from multiple color centres coupled to such cavities. Such quantum-photonic randomness provides robustness against modelling and side-channel attacks employing machine learning by remote-hackers and can be used to generate a framework of securing biomedical Internet of Things devices and architecture.
In spite of numerous advantages offered by Quantum Dot (QD) based imaging systems in infrared photo-detection, the physical realization of such systems has always been a challenging task. In this study, we aim to analyze the effects of growth rate variation on the structural and optical properties of self-assembled InAs/GaAs Stranski-Krastanov (SK) QDs grown on semi-insulating GaAs substrate using MBE (Molecular Beam Epitaxy). Five samples grown at a substrate temperature of 490°C with varying growth rates (0.025ML/s, 0.05ML/s, 0.075ML/s, 0.1ML/s, 0.15ML/s) were investigated using PL spectroscopy, and AFM measurements. PL spectroscopy showed a blue shift in the ground state peak wavelength with an increase in growth rate which was further corroborated by AFM measurements, showing reduced dot-size with an increased growth rate. AFM measurements showed an increase in dot density with an increased growth rate suggesting increased tendency towards nucleation. Integrated PL intensity witnessed an initial increase with an increased growth rate before achieving its maxima for sample grown at 0.075ML/s, rendering the sample grown at 0.075ML/s best in terms of optical activity. These observations provided key insights into the growth kinetics operating during dot-formation through SK growth mode by evaluating the competition between the forces due to surface diffusion and nucleation.
InAs/GaAs Quantum Dots have piqued the interest of researchers owing to the advantages they offer in the fabrication of highly efficient optoelectronic devices. In this study, we aim to examine the consequence varying V-III ratio on optical and structural behavior of self-assembled InAs/GaAs Stranski-Krastanov (SK) Quantum Dots grown on GaAs substrate using Molecular Beam Epitaxy (MBE). Three samples consisting of three layers of vertically stacked Quantum Dots with three different V-III ratios (48, 60 and 80 respectively) grown at a substrate temperature of 490°C have been thoroughly examined using PL spectroscopy and HR-XRD. The best optical response is seen in the sample with 80 as VIII ratio. A higher As vapor pressure during growth seems to suppress the surface migration of Indium atoms leading to bigger dot size, increased PL intensity and more uniform distribution rendering better optical response. The absence of satellite peaks in HR-XRD measurements of sample with lower V-III ratio indicates significant density of point-defects. HRXRD analysis reveals an increase in perpendicular strain with greater V-III ratio. Reduced FWHM in sample with higher V-III ratio is in accordance with suppressed Indium diffusion and strain propagation across multi-layered nanostructure contributing to greater uniformity in dot-size. PL spectrum of sample with least V-III ratio shows sharp peaks around 900 nm indicating incomplete dot-formation at such low ratios leaving significant part of wetting layer exposed. Our investigation provides interesting insights into kinetics of nanostructure growth which will prove to be helpful in fabrication of optimized nanostructures.
The effect of substrate temperature variation on properties of InAs/GaAs Quantum Dots has been studied. Increase in substrate temperature during growth leads to blue-shift in the PL spectrum which becomes fairly evident after a threshold substrate temperature. Beyond the threshold substrate temperature (beyond 500°C), the effects due to Indium desorption cannot be neglected and hence they contribute to poor optical quality of dots as evident from reduced integrated PL intensity on increasing substrate temperature. AFM measurements also corroborate these findings showing reduced dot size and higher dot density after threshold substrate temperature. We suggest an optimum substrate temperature around 480 ″C for growth process.
Modulation doping or localization of carriers in the detector or solar cell structure is an interesting technique which has piqued the interest of researchers. In this study, we demonstrate the effect of modulation doping on InAs/GaAs p-i-p QDIP grown on semi-insulating GaAs substrate using MBE. The active region consists of 10 layers of 2.7 ML InAs quantum dots followed up with 60 nm GaAs capping layer. In the GaAs capping, a modulation p-doping of 3 nm was introduced at 7, 12 and 17 nm from the InAs dot layer thus forming sample A, B and C, respectively. The ground state emission peak at 19 K from photoluminescence (PL) spectroscopy was measured at 1055.5, 1057.5 and 1062 nm for sample A, B and C respectively. Activation energies calculated from temperature dependent PL spectra were 157.57, 167.18 and 146.63 meV for the respective samples. The fabricated single pixel detectors exhibited spectral response peak from 1 to 3.5 μm in short wave infrared (SWIR) region for all the samples. The spectral response peaks observed were at 2.01 and 2.43 μm for device A, at 1.83 μm for device B and at 1.77 μm for device C. Highest operating temperature obtained from device A, B and C were 100K, 150K and 200K, respectively. The peak responsivities observed at 100K were 0.503, 0.154 and 0.33 A/W for the device A, B and C, respectively. Optimizing the position of localized carriers introduced in the active region can achieve the tunability in detection peak.
Quantum dots based infrared photodetectors (QDIPs) having intra-valence band transitions and holes as majority carriers have been explored in this work. Here, we are demonstrating the effect of modulation doping on p-i-p QDIP (InAs/GaAs) grown using molecular beam epitaxy (MBE). The active region of the detector consists of 10 layers of selfassembled InAs quantum dots (2.7 ML) capped with GaAs layers and embedded in between p-type (beryllium-doped) GaAs layers. The performance of InAs/GaAs p-i-p QDIP (device A) was compared with modulation doped InAs/GaAs QDIP (device B). In the case of device B, modulation doping with p-type GaAs was introduced after growing 7nm of GaAs capping. The ground state emission peak at 10 K from photoluminescence spectroscopy was measured at 1060.5 nm and 1055.5 nm with a thermal activation energy of 222.93 meV and 157.57 meV for sample A and B, respectively. The measured dark current density at 75 K was 0.448 and 1.012 A/cm2 at -1 V for device A and B, respectively. Spectral response peak in short wave infrared region (1.5 to 2.5 μm) were observed from both devices but in the case of device B, the spectral peaks were visible in mid wave infrared regime as well. At 75 K, the peak responsivity value measured was 35.11 A/W (at -1.5 V) and 0.333 A/W (at -1.5 V bias) for device A and B, respectively. High temperature of operation upto 200 K was observed from Device A whereas Device B exhibited response up to 125 K. Modulation doping close to the InAs quantum dots deteriorates the device performance.
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