Papers by Debiprasad Panda
Quantum Dots, Nanostructures, and Quantum Materials: Growth, Characterization, and Modeling XVII, 2020
We are studying here the heterogeneously coupled Submonolayer (SML) on Stranski-Krastanov (SK) qu... more We are studying here the heterogeneously coupled Submonolayer (SML) on Stranski-Krastanov (SK) quantum dot (QD) heterostructures. The consolidation in SML on SK heterostructure has been observed by varying growth rate as 0.05 and 0.1 ML/sec. The barrier thickness between SK and SML QDs has also been varied as 5, 7.5, and 10 nm. Pphotoluminescence(PL) study shows transition of carriers with dot size distribution. The peak from SK QDs is prominent in PL spectra of both growth rate samples. The absence of SML peak from the PL might be due to the tunnelling of carriers from SML to SK QDs, which follows the SK ground energy states for recombination. SML peak is visible only in low growth rate sample for barrier thickness of 10 nm, as with higher barrier thickness there is reduction in the probability of tunnelling of carriers. Samples with lower growth rate shows bimodal dot size distribution at barrier thickness 7.5nm, whereas higher growth rate samples shows monomodal dot size distribution. Compressive strains were extracted from high-resolution X-Ray diffraction (HRXRD) measurement. From the HRXRD measurement, it has been found that the strain decreases with increasing barrier thickness. Low growth rate samples have less strain as compared to high growth rate samples. In the lower growth rate samples, PL peak is red shifted as compared to higher growth rate samples due to less strain in the heterostructures and larger size QDs. Therefore, this study will be useful for advanced optoelectronic applications.
Low-Dimensional Materials and Devices 2019, 2019
Hybrid coupled quantum dot (QD) structures have a high absorption coefficient along with the mini... more Hybrid coupled quantum dot (QD) structures have a high absorption coefficient along with the minimum cumulative strain in the heterostructure compared to that in the homogeneously coupled heterostructure of only Stranski-Krastanov (SK) QDs. Here, we are introducing a theoretical analysis of the hybrid heterostructure consisting of six submonolayer (SML) stacks above SK QDs with a various capping layer combinations. Sample A (InGaAs-InGaAs) has both SK and SML capping layers of InGaAs. Similarly, Sample B (InGaAsInAlGaAs), sample C (InAlGaAs-InGaAs), and sample D (InAlGaAs-InAlGaAs) have variations in the capping composition of SK and SML dots. The barrier thickness between SML stacks and SK dots is taken to be 7.5nm, and the capping layer thickness of the SK dot is 3nm. The number of SML stacks and barrier thickness has been optimized from our previous experimental work. Hydrostatic and biaxial strains of four samples are analyzed and compared. It has been found that sample D shows the lowest magnitude of hydrostatic strain in both SML and SK dots, suggesting better carrier confinement in both QDs. Moreover, Sample D has the highest biaxial strain in the SK dot indicating the maximum splitting of the valence band which leads to a lower band gap in the sample. Thus, after optimizing all the performance parameters, we found that Sample D could be the potential candidate for optoelectronic device applications.
Inorganic Chemistry Frontiers, 2021
Methods for the straightforward, room temperature synthesis of UO2+x nanoparticles and thin films... more Methods for the straightforward, room temperature synthesis of UO2+x nanoparticles and thin films using solution processable, molecular uranium(IV) compounds is described. Ultra-small uranium dioxide nanoparticles are synthesized from the hydrolysis...
Superlattices and Microstructures, 2020
Currently, a number of promising strategies and approaches to cancer treatment include differenti... more Currently, a number of promising strategies and approaches to cancer treatment include differentiation therapy. However, theoretical and methodological foundations of this field are not yet well developed. The objective of this study was to determine the effects of a mixture of polyclonal activators (PAs; phytohaemagglutinin, concanavalin A and lipopolysaccharide) on cytokine production by biopsy samples of invasive breast carcinoma of no special type (IBC-NST) having various differentiation abilities and metastatic potentials as well as on differentiation status of the IBC-NST biopsy samples. We used ELISAs to investigate spontaneous and PA-stimulated cytokine production in the IBC-NST biopsy samples; from these data, we calculated a cytokine production stimulation index (SIPA). The effect of PAs on tumour cell differentiation was determined via a differentiation stimulation index (DSI). DSI was found to vary within the range 1.0-5.0. After treatment with PAs, in the IBC-NST biopsy samples of group I (DSI <1.25), the production of IL-2, IL-6, IL-8, IL-17, IL-18, IL-1β, IL-1Ra, TNF-α and GM-CSF increased; in the biopsy samples of group II (DSI >1.25), the production of IL-6, IL-1β, IL-1Ra, TNF-α, G-CSF and GM-CSF significantly increased, while the production of VEGF-A decreased. Receiver operating characteristic (ROC) analysis of SIPA revealed that increased production of IL-18 in the IBC-NST biopsy samples after exposure to PAs may block the PA-driven, cytokine-mediated differentiation of moderately differentiated into highly differentiated tumour cells. The ROC analysis also uncovered an association between the responses of tumour cells to PAs and lymph node metastasis observed in the patients. The findings suggest that there is a need for research aimed at finding new drugs for differentiating cancer therapy and at searching for targeted inducers of cytokine production or specific suppressors of their induction.
Journal of Luminescence, 2021
Abstract Strain-coupled multilayer Quantum Dot (QD) structures draw a great attention these days ... more Abstract Strain-coupled multilayer Quantum Dot (QD) structures draw a great attention these days because of their superior optical and device performance. However, these coupled multilayer QD structures have limitations such as non-uniform QD size distribution, defects, and dislocations due to the propagation of strain in QD layers. Furthermore, the carrier relaxation lifetime must be improved in these coupled QD structures for sought-after device performance. This study serves for three main purposes. Firstly, we have utilized a growth strategy to maintain the overgrowth percentage such that the Stranski-Krastanov (SK) QD dimensions in every layer is same for all the multilayer structures. Secondly, these multilayer SK QDs are made to electronically couple with the Sub-monolayer (SML) QDs in such a way that the carrier relaxation lifetime can be increased, that could ameliorate the photoconductive gain and the responsivity. Lastly, the amount of cumulative strain generated inside QDs can be reduced by the incorporation of In0.15Ga0.85As strain reducing layer (capping layer) in a multilayer structure. Five different multilayer structures with single (x1), bi (x2), penta (x5), hepta (x7), and ten-layers (x10) of SK QDs electronically coupled to six stacks of SML QDs are used in this study. Photoluminescence (PL) studies reveal that the SK QD dimensions is maintained to be the same in all multilayer structures due to the proposed growth strategy, which is also observed through transmission electron microscopy (TEM) images. Photoluminescence excitation (PLE) analysis shows the match of excited states of SK QDs to the ground state of the SML QDs, aiding the carrier tunnel phenomena. The ω/2Ө measurements from high resolution X-ray diffraction (HRXRD) is carried out to calculate the overall strain in the grown heterostructures. The optical properties and the strain components obtained from the nextnano simulation tool are in good agreement with the experimental results. Thus, coupled multilayer QD structures with a growth strategy in the current study would be more suitable for the realization of quantum dot infrared photodetectors and intermediate band solar cell applications accommodated with high device efficiency.
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XVI, 2019
Modulation doping or localization of carriers in the detector or solar cell structure is an inter... more 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, Nanostructures, and Quantum Materials: Growth, Characterization, and Modeling XVII, 2020
Self-assembled InAs quantum dot (QD) based heterostructures have been emerged as a potential cand... more Self-assembled InAs quantum dot (QD) based heterostructures have been emerged as a potential candidate for optoelectronic device application over last decade due to the three dimensional carrier confinement. Here, we qualitatively demonstrate the effect of growth rate of both QD and capping layer on the photoluminescence (PL) result of MBE grown InAs/GaAs QD heterostructures. The investigated samples are having 2.7 monolayer (ML) near-surface InAs QDs. The InAs QDs in samples A and B are grown with growth rates of 0.2 and 0.1 ML/sec respectively, whereas growth rate of the GaAs capping layer is kept constant (0.62 μm/hr) in both samples. In sample C, QD and capping layer are grown at 0.2 ML/sec and 1.13 μm/hr, respectively. Sample B exhibited lower full-width half maximum of ground peak (36 nm) as compared to sample A (40 nm). This indicates better homogeneity in dot size distribution in sample B, which has a lower growth rate of QDs. Moreover, sample C with higher growth rate of capping layer showed red-shift in PL as compared to sample A. It can be inferred that the growth rate of capping layer affects the composition of QDs by suppressing In diffusion from QDs towards the capping layer. However, sample C showed decrement in PL intensity and it could be attributed to the dissolution of dots due to higher growth rate of capping layer. There is trade-off in optimization of growth rate variabilities of both QDs and capping layer.
Infrared Technology and Applications XLIV, 2018
In the present work we are introducing heterogeneously coupled InAs stranski-krastanov and submon... more In the present work we are introducing heterogeneously coupled InAs stranski-krastanov and submonolayer quantum dot as an active material for quantum dot based infrared photodetector. Initially, we have optimized the basic SK on SML heterostructure. The thickness of the GaAs barrier layer is varied from 2.5 to 7.5 nm to tune the vertical coupling between seed SML and top SK QDs. PL and PLE response confirms the carrier tunneling between these heterogeneous QDs. The vertical alignment of SML and SK QDs is shown in Cross sectional TEM images. The sample with 7.5 nm barrier layer is incorporated into a N-I-N based quantum dot infrared photodetector, which shows broader spectral response than standard SK QD based IR detectors.
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XVI, 2019
In this study, we demonstrate the device performance of modulation doped InAs/GaAs p-i-p QDIP (de... more In this study, we demonstrate the device performance of modulation doped InAs/GaAs p-i-p QDIP (device A) and the effect of thin 1 nm quaternary (InAlGaAs) capping on the same heterostructure (device B). The ground state emission peak at 9 K from photoluminescence spectroscopy was measured at 1055.1 nm and 1046.4 nm for sample A and B, respectively. The measured dark current densities at 75 K for an applied bias of -1 V were 1.079 A/cm−2 and 0.038 A/cm−2 for device A and B, respectively. The fabricated single pixel detectors from device A exhibited emission peak in short wave infrared regime whereas whereas device B exhibited a multicolour spectral response from short wave (SWIR) to mid wave infrared (MWIR) region. The measured spectral peaks at low temperature were at 2 and 2.39 μm for device A and at 2.013, 2.49, 3.49 and 4.36 μm with a dominant peak in SWIR region for device B. Both the devices exhibited spectral response peak up to 75K with a responsivity of 0.832 A/W for device A compared to that of 0.545 A/W for device B at -2.5V bias. Tunability in detection peak with improvement in device performance was achieved by incorporating additional quaternary capping.
Low-Dimensional Materials and Devices 2019, 2019
InAs/GaAs Quantum Dots have piqued the interest of researchers owing to the advantages they offer... more 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.
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XVI, 2019
Sugarcane is the important commercial crop of the country. India is the largest consumer of sugar... more Sugarcane is the important commercial crop of the country. India is the largest consumer of sugar in the world, and the second largest producer, after Brazil (India Sugar Trade Industry, 2013) and produces more of cane sugar and not beet sugar. The main objectives of the study are to examine the economics of sugarcane cultivation and to identity the major constraints faced by sugarcane cultivators. To fulfill the above said objectives both primary and secondary sources of data has been used in this research work. The researcher revealed that the cost of seeds and harvesting are high as a result the total cost of production is also high. The study also highlighted that shortage of labour, high wage rate of labour and low price are the important problems faced by the farmers of the study area.
Low-Dimensional Materials and Devices 2019, 2019
In this report, the performance of Quantum Dot Infrared Photodetector (QDIP) is examined in which... more In this report, the performance of Quantum Dot Infrared Photodetector (QDIP) is examined in which the active layer consists of 10 layers of uncoupled InAs quantum dots (QDs) with quaternary In0.21Al0.21Ga0.58As capping. The optical, structural, and electrical properties of the QDIP is observed and compared with a sample in which the QDs are capped with binary GaAs layer. The observation of full width half maximum (FWHM) in the low-temperature photoluminescence (PL) of both sample shows a change in dot size distribution. Variation in the dot size distribution is also observed from the low temperature power dependent PL. Activation energy calculated from the temperature dependent PL indicates better carrier confinement in the structure with In0.21Al0.21Ga0.58As capped QDs. This can be explained by the formation of higher barrier potential. Stain introduced due to lattice mismatch in the heterostructure is calculated from the high resolution X-ray diffraction (HRXRD) Rocking curves, which shows a relatively low value of strain in the QDIP heterostructure with In0.21Al0.21Ga0.58As capping with respect to the QDIP with GaAs capping layer. A five order reduction in the dark current density is also observed form the QDIP with In0.21Al0.21Ga0.58As capping due to insertion of Al in the capping layer. The dark current obtained for the In0.21Al0.21Ga0.58As capped QDIP is 1.9E-5 A/cm2, whereas the same for the GaAs capped QDIP is 4.91 A/cm2. This attributes to the confinement enhancement in the prior QDIP heterostructure.
2018 3rd International Conference on Microwave and Photonics (ICMAP), 2018
Infrared photodetectors with strain-coupled quantum dot structure have better optoelectronic prop... more Infrared photodetectors with strain-coupled quantum dot structure have better optoelectronic properties compared to the conventional uncoupled structure. In this report, the strain profile and optoelectronic properties have been compared between the strain coupled Trilayer InAs and InGaAs quantum dot infrared photodetectors. The device with InGaAs QDs in its active layer, has longer luminescence peak and better dot formation due to less lattice mismatch between the dot and capping material. Thus, InGaAs based QDIPs would provide better infrared imaging with higher efficiency.
Quantum Dots, Nanostructures, and Quantum Materials: Growth, Characterization, and Modeling XVII, 2020
Heterogeneously coupled SK-SMLQuantum Dot (QD) heterostructures has superior characteristics comp... more Heterogeneously coupled SK-SMLQuantum Dot (QD) heterostructures has superior characteristics compared to homogeneously coupled SK QDs in terms of dot density, cumulative strain and absorption efficiency. Here, we have carried out a comparative analysis between heterogeneously coupled SK on SML and SML on SK QDs heterostructures. The barrier thickness between SK and SML QDs, in both structures, has been varied as 5, 7.5 and 10 nm. The tunnelling of carriers from one type of QD (SK/SML) to another type of QD (SML/SK)has been explicated through photoluminescence (PL) study. The appearance of SML peak along with the SK peak for higher barrier thickness has been observed in case of SK on SML QD heterostructure. This might be due to decrease in tunnelling probability of carriers and thereby, transition takes place from both SK and SML QDs. However, this phenomenon has not been observed in SML on SK QD heterostructures. The reason might be the reduced average barrier thickness between SML and SK QDs, which allowed tunnelling of all the carriers. Thus, SML peak was absent in all three SML on SK QD heterostructures. Moreover, strain distribution in all the heterostructures have been investigated through high resolution X-ray diffraction (HRXRD) measurements. The significant modification in structural morphology of QDs, can be obtained fromHRXRD, clearly demonstrates variation in strain with respect to barrier thickness. This comparative analysis would help the research community to choose the optimized heterostructure for desired optoelectronic applications.
The InAs quantum dots (QDs) with dot-in-well (DWELL) structure are preferable than the convention... more The InAs quantum dots (QDs) with dot-in-well (DWELL) structure are preferable than the conventional InAs QD heterostructures because of the carrier funneling mechanism in the DWELL structure. There are few reports on the InAs DWELL quantum dot infrared photodetectors (QDIPs). However, a complete study on the optimization of the well structure and thickness is still missing in the literature. Here, we report the optimization of InAs DWELL heterostructure for superior structural and optical properties. We have simulated the DWELL heterostructures by varying the thickness of In0.15Ga0.85As well in both sides of the InAs QD. The symmetric DWELLs with 2/2, 4/4, 6/6, 8/8, and 10/10 nm InGaAs well are considered. For the asymmetric DWELL, the underlying well is kept fixed at 2 nm, whereas the upper well thickness is varied as 4, 6, 8, and 10 nm. A decrease (increase) in the hydrostatic (biaxial) strain is observed as the well thickness is increased in both symmetric and asymmetric DWELL st...
This study is focused on structural and optical properties of multilayer InAs/InGaAs dot-in-a-wel... more This study is focused on structural and optical properties of multilayer InAs/InGaAs dot-in-a-well (DWELL) heterostructure with varying capping layer thickness. Two samples A and B are considered with 2 monolayer (ML) InAs quantum dots (QDs). The top InGaAs capping layer thickness is varied from 6 to 8 nm from sample A to B, whereas the lower well thickness was kept constant at 2 nm. The ground-state peak in the photoluminescence (PL) spectra shows a blue shift with increased capping layer thickness (sample A: 1148 nm, sample B: 1140 nm). This blue shift is due to the increased well layer thickness, which leads to higher strain and shrinkage in dot size. The activation energy (Ea) is calculated from the temperature dependent PL results using the Arrhenius equation. The activation energy of sample A and B are 181 meV and 152 meV respectively. The higher activation energy leads to a reduction in dark current, which affirms that sample A would be better for the device application. Rama...
In this work, we have proposed two ex-situ treatments to annihilate bulk defects and non-radiativ... more In this work, we have proposed two ex-situ treatments to annihilate bulk defects and non-radiative surface states in MBE grown AlGaN nanowires on silicon substrate. Vertically aligned nanowires were grown by molecular beam epitaxy (Veeco Gen II) system, equipped with RF plasma source for incorporating nitrogen, at a substrate temperature of 8000C. The nanowires were structurally characterized by SEM images and an areal density of 3.8×109 nanowires-cm-2 was calculated. The peak emission wavelength was measured to be 343nm at 19K from photoluminescence (PL) measurements. The as-grown nanowires were implanted with H- ions at various energies and fluences. A 2-fold increase in PL intensity without any wavelength shift was found in sample with irradiated energy of 3 MeV and a fluency of 1×1012 ions-cm-2. X-Ray diffraction measurements on (002) diffraction peak give an FWHM of 1440 arc-sec for ionimplanted samples as compared to 1872 arc-sec for as-grown nanowires indicating an improvemen...
The hydrostatic (εhy) and biaxial (εbi) strain in lateral (x) and growth (z) direction have been ... more The hydrostatic (εhy) and biaxial (εbi) strain in lateral (x) and growth (z) direction have been computed and compared for InAs quantum dot (QD) with different capping. The capping layers are: GaAs, InGaAs/GaAs, InAlGaAs/GaAs, InGaAs/InAlGaAs/GaAs, InAlGaAs/InGaAs/GaAs, and the total thickness is kept constant for all QD structures. The strain distribution is mainly confined within the dot and dies down towards the capping layer. The movement of conduction band edges is controlled by hydrostatic strain. QDs capped with InAlGaAs/InGaAs/GaAs and InAlGaAs/GaAs shows lower magnitude of εhy, which indicates better carrier confinement as compared to other capping. The electrostatic potential obtained for the InAlGaAs capped QDs is larger (~0.5 V) than other structures. The valence band splitting into the heavy hole and light hole depends on the biaxial strain. It is observed that GaAs and InAlGaAs/InGaAs/GaAs capping has the smallest and largest values of εbi respectively in the growth di...
In this study, we report high temperature operation of infrared photodetector using p-i-p InAs/Ga... more In this study, we report high temperature operation of infrared photodetector using p-i-p InAs/GaAs quantum dots. The ground state emission peak at 18 K from photoluminescence spectroscopy was measured at 986 nm. Single pixel detectors were fabricated and device characteristics like temperature dependent dark current, blackbody and spectral response were analyzed. The measured dark current density at 220 K with applied bias of 0.2 V was 2.48×10-3 A/cm2. The spectral response peak (2 μm) was observed in short wave-infrared (SWIR) region. We report an excellent SWIR detection characteristics at 220 K with a responsivity and specific detectivity of 3.81 A/W and 2.18×1010 cmHz1/2/W, respectively. The spectral response peak was achieved till 250 K and blackbody signal was observed till 270 K.
Photoluminescence (PL) and Photoluminescence excitation (PLE) measurements have been carried out ... more Photoluminescence (PL) and Photoluminescence excitation (PLE) measurements have been carried out to investigate the carrier recombination pathways in a GaAs capped InAs quantum dot (QD) and an InAs dot in InGaAs well (DWELL) structure. The presence of an InGaAs quantum well (QW) results in an anomalous behavior in the temperature dependent PL spectra. The carrier trapping in the InGaAs well at low temperature and the redistribution of these carriers as the temperature rises is well explored through the temperature dependent PL spectra. The existence of additional energy states due to the incorporation of an InGaAs QW has been observed through the PLE result and explained schematically. Cross-sectional transmission electron microscopy provides a direct evidence of the formation of hybrid thick QW structure due to the intermixing of InGaAs well and the InAs wetting layer (WL). The strain relaxation in the DWELL structure is substantiated from the simulated strain profile as well as th...
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Papers by Debiprasad Panda