The current work shows a novel multilayer heterostructure with Stranski-Krastanov (S-K) quantum dots (QDs), which shows the relatively superior performance in terms of strain reduction and propagation, and optical emission. Here, 2.7 ML InAs/GaAs(Sb) multilayer S-K QDs heterostructures are grown by employing a solid-source Molecular Beam Epitaxy (MBE) system. The multilayer heterostructures consist of single, bi, and hepta-layer S-K QDs with an adaptation of novel growth strategy by estimation of overgrowth percentage. Such overgrowth percentage optimization and new growth strategy is able to grow uniform dots in reach layer from bottom to top layer and residual strain is reduced with the increasing QD layers. To maintain the similar overgrowth percentage (33%) throughout the heterostructures, monolayer coverage is maintained to be 2.5 ML from just next layer of bottom QDs layer to top for each multilayer heterostructures. The simulation is done by Nextnano software for all the heterostructures to analyse the strain propagation, and bandalignment in depth and all results exhibit that residual strain are almost constant after bi-layer with maximum blue-shift in ground-state emission peak. Low-temperature (19 K) Photoluminescence (PL) measurements are performed to investigate the optical properties of the heterostructures and ground state peaks are found at ~ 1084 nm, which confirms the uniform S-K QDs for all the heterostructures. However, lowest FWHM and highest absorptivity are obtained for hepta-layer heterostructures. Further, HRXRD peaks and corresponding values of strain confirm the enhancement of crystallinity and smooth interfaces with significant amount of reduction in strain for multilayer heterostructures.
The current work represents the influence of Sb composition on strain profiles, band alignment of InAs/GaAsSb Stranski-Krastanov (SK) quantum dots (QD) heterostructure. A single layer InAs/GaAs SK QD heterostructure has been utilised as a reference structure (sample A). Three different structures B, C and D are chosen with the Sb composition of 10%, 14% and 22% in the capping layer on the InAs QDs. The strain distribution of InAs quantum dots with GaAs1-xSbx capping has been investigated in detail by using Nextnano simulation software. The transition from type-I to type-II band alignment occurs after 14% Sb incorporation. The effect of variation in the Sb component on the strain profile is analysed in terms of hydrostatic and biaxial strain. In the strain profiles, the biaxial strain increases significantly from samples A to D, whereas the hydrostatic strain is reducing from samples A to D inside the QD region simultaneously. Further, low temperature photoluminescence (PL) has been performed to validate the simulated results. The PL peak is originated at ~1030 nm for sample A, which shows a good agreement with the simulated value ~1071 nm. With the similar dot size, the simulated PL peaks are found at 1116, 1284, 1675 nm for samples B, C and D, respectively. A slight variation is observed in the experimentally obtained PL peaks and simulated one due to the incorporation of higher Sb content. With the higher Sb content, relatively more defects are generated, which affects the experimental PL peaks. Also, a red shift is found in the PL peaks from ~1030 nm to ~1213 nm at 19K and it gives an insight to develop various optoelectronic devices using such QDs heterostructure.
In the past decade, surface quantum dots (SQDs) have been thoroughly investigated for sensing applications. The SQDs suffer from the limitations of non-uniformity dot distribution and weak oscillator strength, which affect their response to ambient contaminants. We have achieved uniformity by coupling buried quantum dots (BQDs) with SQDs. Moreover, BQDs provide additional carriers to SQDs for enhancing sensitivity. In this study, we have theoretically investigated the impact of varying the capping material of BQDs on their strain and optical properties. Investigations have been carried out with three samples having different capping materials as GaAs (sample A1), InGaAs (sample A2), and InAlGaAs (sample A3). A decreasing trend in the magnitude of hydrostatic strain and an increasing trend in biaxial strain inside the BQD from samples A1-A3 is observed. With a decrease in hydrostatic strain, the conduction band eigenstate lowers towards the band edge resulting in a lowering bandgap. With an increase in biaxial strain, the bandgap lowers due to the heavy hole (HH) and light hole (LH) band splitting. The lowering of the bandgap enhances the luminescence of BQD in sample A3. The computed photo-luminescence (PL) emission wavelength is found to be 1547 nm, 1558 nm, and 1568 nm for GaAs, InAlGaAs, and InGaAs capping respectively. The lowering in the bandgap of BQD leads to band alignment between SQD and BQDs, which may improve the carrier communication between these layers and become a promising candidate for better carrier reservoirs for SQDs in sensor applications.
In this work, the concept of the novel approach called linear alloy capping layer (LACL) has been investigated on the strain-coupled bilayer InAs/GaAs1-ySby QD heterostructures. Here, two analog structures with low (structure BA1) and high (structure BA2) antimony (Sb) contents, and one linear alloyed structure (BL) with varying Sb-content inside the capping layer is considered. The Sb-content inside the CL of structure BA1 and BA2 are 10% and 20%, respectively. Whereas, it is varying linearly from 20% to 10% inside structure BL. The CL and GaAs spacer layer thickness has been taken as 8 nm and 13 nm, respectively. All these three structures have been modeled using Nextnano++ simulation software. Two strain components, hydrostatic and biaxial have been computed and compared. These two strain components help in decreasing the ground state energy gap which leads to a red-shifted PL emission. The structure BL offers improved biaxial strain by 1.11% and 0.56% inside QD compared to structures BA1 and BA2. In addition, the magnitude of hydrostatic strain inside QD of structure BL is reduced by 1.78% and increased by 0.64% compared to structures BA1 and BA2. The strain inside the CL of structure BL is reduced very smoothly in a linear fashion as compared to other analog structures. The computed PL emission of structures BA1, BA2, and BL are 1371 nm, 1665 nm, and 1617 nm, respectively. Also, the proposed structure BL offers a type-II band profile. Hence this proposed approach is useful for future optoelectronic applications.
In current study, the variation of sub-capping thickness of InGaAs strain reducing layer (SRL) of InAs quantum dot heterostructure using digital alloy approach is presented. The thickness of 6 nm SRL of conventional structure (sample A) is divided equally with 2 nm thickness (sample B) by using digital alloy approach. Further, using such approach, this thick 6 nm capping is divided in unequal fashion for sample C (1 nm, 2 nm and 3 nm) and sample D (3 nm, 2 nm and 1 nm) from InAs QD towards top GaAs layer. The In-content inside the SRL of the sample A is 15%, whereas, In-content inside the divided-SRL is considered as 45%, 30% and 15% for all other samples. Such composition of SRLs helps in reducing the In-out diffusion, minimizing the lattice mismatch at InAs QD-SRL and SRL-top GaAs layer interfaces, and also reduces the strain inside the overall heterostructures. Two strains, namely hydrostatic and biaxial are calculated by using Nextnano for all the structures and compared simultaneously. The hydrostatic strain inside the QD of sample D is reduced by 4.74%, 1.07% and 2.269% and the biaxial strain inside the QD of sample D is improved by 1.66%, 0.696% and 1.276% as compared to that of samples A, B and C, respectively. The computed PL emission of samples A, B, C and D are observed to be 1305 nm, 1365 nm, 1349 nm and 1375 nm, respectively. Hence, sample D is the optimum choice for fabricating future opto-electronic devices.
A comparative study of Stranski-Krastanov (SK), sub-monolayer (SML) and coupled SK on SML InAs quantum dots as active region in InGaAs/GaAs/AlGaAs DDWELL heterostructure was done. Incorporation of additional high band gap confinement enhancing (CE) AlxGa1-xAs barrier helps to create new energy levels, increase the absorption coefficient, reduce dark current and improve crystalline quality of the heterostructure. This is because of the CE barrier which reduces In-adatom out-diffusion. Three different DDWELL heterostructure A, B and C with active regions as SK, SML and SK on SML respectively, had been modelled using the Nextnano simulation tool keeping all other parameters same. Photoluminescence (PL) emission wavelength, biaxial strains and hydrostatic strain profiles of heterostructures A, B and C were compared. Hydrostatic strain with less magnitude leads to better carrier confinement within the conduction band, and biaxial strain with high magnitude increases splitting between heavy-hole and light- hole bands, generating a red-shift in PL emission wavelength. It can be observed from the computed result that biaxial and hydrostatic strain in the SK QD are enhanced in structure C compared to A. Likewise, biaxial strain and hydrostatic strain in the SML QD stacks are enhanced in structure C compared to B. PL emission wavelength of structures A, B, and C were observed to be 1116nm, 864nm and 1170nm respectively. Therefore, structure C exhibits minimum strain among the heterostructures and highest PL emission wavelength for SWIR applications.
In this study, the author proposed a new technique for strain minimization, called linear alloy technique (LAT), for the symmetric dot-in-a-well (DWELL) heterostructure. Here, three different DWELL InAs QDs heterostructures with 6 nm thick InxGa1-xAs as well material have been simulated using 8 band k.p. model-based Nextnano software. Here, the first sample is analog alloyed DWELL heterostructure having In0.15Ga0.85As well (Sample A), the second sample is digital alloyed DWELL heterostructure where the well layer is divided into three sub-layers of 2nm thickness with indium composition varied from 45% to 15% in the step of 15%(Sample D), and the third sample is linear alloyed DWELL heterostructure where indium composition is varied from 45% to 15% (Sample L) in linear fashion have been studied. The Lower the magnitude of hydrostatic strain better will be carrier confinement. The more the biaxial strain, the more the heavy-hole and light-hole band splitting, which reduces the transition energy gap. The computed biaxial strain is increased by 1.52% and 2.21%, and the magnitude of hydrostatic strain is reduced by 3.66% and 1.13% in sample Lcompared with samples A and D, respectively. Strain inside the well layer of sample L reduces more smoothly than samples A and D, respectively. The computed PL emission wavelength for all three samples are 1329, 1418, and 1419 nm for the samples A, D, and L, respectively. Hence, this proposed technique can be the best choice for fabricating future optoelectronicbased devices.
In this study, we minimize the strain by using the new technique called linear alloy technique (LAT) for the Stranski-Krastanov (SK) quantum dot heterostructure. Here, three different SK InAs QDs heterostructures with 6 nm thick capping layer (CL) having InxGa1-xAs as capping material have been simulated using the 8-band k.p. model-based Nextnano software. Here, the first sample is analog alloyed SK QDs heterostructure having In0.15Ga0.85As capping (Sample A1), the second sample is digital alloyed SK QDs heterostructure where CL is divided into three sub-layers each of 2nm thickness with indium composition varied from 45-30-15% (Sample D1), and the third sample is linear alloyed SK QDs heterostructure where indium composition is varied from 45% to 15% (Sample L1) in a linear fashion, have been studied. The biaxial and hydrostatic strain is computed for all three heterostructures and compared. The biaxial strain is improved by 2.03% and 2.0%, and hydrostatic strain is reduced by 3.49% and 0.071% inside the QD region of sample L1 compared with samples A1 and D1, respectively. Additionally, digital sample D1 offers a step-wise strain reduction inside CL compared to analog sample A1. However, sample L1 offers an even more relaxed strain inside CL than samples A1 and D1, respectively. The PL emission wavelength is observed at 1317, 1372, and 1379 nm for samples A1, D1, and L1, respectively. Hence the linear alloy technique is useful for making future optoelectronic devices where strain reduction is the main factor.
In this study, variation in Sb composition in In0.18Ga0.82AsYSb1-Y as capping layer (CL) over SK QDs and matrix material (MM) in 6 stacks of SML QDs for InAs SML, and strain coupled InAs SK-on-SML QDs heterostructure have been done theoretically. The structural and optical properties have been investigated through Nextnano++ software. Different single-layer SK (A-series), SML (B-series), and coupled SK-on-SML QDs (C-series) structures have been modeled for this study. Two main strain components, hydrostatic and biaxial strain have been computed simultaneously with the solution of 3-D Schrodinger’s equation. The hydrostatic strain is compressive in the growth direction and gives information about carrier confinement in the conduction band while a biaxial strain is tensile in the growth direction and gives information about splitting in the valance band. There is a significant improvement of hydrostatic and biaxial strain observed for A-series and B-series structures respectively, which have quaternary capping, which helps in reduced overall strain and reduced InAs QDs desorption. In Addition to that, the coupled SK-on-SML structures (C-series) with InGaAsSb (Sb-15 and 25%) as capping layer and matrix layer possess more biaxial strain and reduced hydrostatic strain as compared to the conventional coupled structures with InGaAs as matrix material of SML and GaAs as capping layer over SK. The computed PL emission wavelength for proposed C-series structures offers a red-shift over conventional coupled structures. These configurations show type-II band alignment which can be used for various optoelectronic applications in the SWIR regime such as solar cells, long-range communication, etc. This study can be advantageous for the optimization of strain-coupled heterostructures.
Stranski-Krastanov (SK) Quantum dots (QDs) based lasers and detectors are now used in many fields because of the plentiful advantages they offer, some of which are normal incident absorption and phonon bottleneck. In order to optimize the properties of the devices, growth parameters have to be tuned properly. The effects of growth temperature (GT) and growth rate (GR) variations on the QD devices have been studied here by comparing simulations and experiments. In this study, InAs QDs are grown on GaAs substrates with four different temperatures, from 480°C to 510°C, and with five different GRs, from 0.15 ML/s to 0.025ML/s. To observe the grown heterostructures' structural and optical properties photoluminescence (PL) and PL excitation (PLE) have been performed on the samples. The size, shape, and composition of the QDs ultimately decide the energy levels in the heterostructure. Hence, it determines the optical and electrical properties of the devices. Here we simulated 3-D strain profiles of the QD and compared the results with PL and PLE. The trends in simulated biaxial strain and heavy hole (HH) - light hole (LH) band splitting, observed in the PLE, match pretty well. We observed that the change in GT drastically affects the composition of the dots and the wetting layer, whereas a change in GR only changes the lateral size of the QDs, and do not affect the strain or composition. These studies can be beneficial for p-i-p short-wave infrared (SWIR) detectors since their spectral response is tuned by the HH-LH band splitting.
A detailed theoretical study of optical and structural properties of heterogeneously coupled Stranski-Krastanov (SK) on submonolayer (SML) QDs heterostructure with In0.18Ga0.82AsYSb1-Y capping on InAs SK QD has been done using Nextnano++ software. Variation of Sb composition was taken as 10, 15, 20 and 25%. By solving 3-D Schrodinger’s equation the biaxial and hydrostatic strain distribution, energy band diagram and PL peak observation is done. It has been noted that increasing Sb composition contributes in transition from type I to type II. This transition can be discovered in positions of probability density function for electron and holes and from energy band illustrations. The biaxial strain is responsible for energy splitting in light hole (LH) and heavy hole (HH) and its distribution in SK QD increases with increasing Sb composition. The hydrostatic strain is compressive strain in nature, which is responsible for carrier confinement in conduction band. With increasing Sb composition the magnitude of hydrostatic strain is observed as diminishing. From the ground state energy levels of electron-hole Eigen state (E1-H1) PL emission wavelength have been observed for all the four structures. It has been noted that higher the composition of Sb, higher the wavelength emission. In overall analysis it has been observed that type-II has lower compressive strain inside the QDs and higher wavelength emission. The composition selection demonstrates both type-I and type-II energy band profile which can be advantageous in many optoelectronic device properties. This theoretical study can be useful in optimization of strain coupled heterostructures for better crystalline quality.
The impact of GaAs1-xNx as a capping layer of InAs quantum dots using digital alloy approach has been investigated. GaAsN capping layer helps in homogeneous distribution of dots on the surface due to formation of nitrogen induced point defects, which helps in minimizing overall compressive strain within the QDs and hence increased dot size. The capping layer of thickness 10 nm with nitrogen composition of 1.8% (Sample A) is considered for analog alloy or conventional approach. The short-period-superlattice (SPS) or sub-divided capping concept has been taken in digital alloy approach for depositing the capping layer. Each SPS is having 2.5 nm thickness and different nitrogen content (1.2%, 1.4%, 1.6%, and 1.8% in each SPS from QD towards top GaAs layer) (Sample D). The hydrostatic and biaxial strain have been computed using Nextnano simulation software and compared for both the mentioned approach. The hydrostatic and biaxial strain in sample D is improved by 0.329% and 0.093% respectively as compare to that in sample A. The observed emission PL wavelength is computed to be 1508 nm and 1430 nm for samples A and D respectively. The simulated PL of sample D is less as compare to that of sample A because of same dot size has been considered for simulation. But as we grow the digital sample using GaAsN material as capping layer, the dot size is increased which in turn helps in red shift in emission PL. Thus, digital alloy approach helps in making devices for future optoelectronic applications.
In this study, we have investigated the effect of varying In-concentration in the barrier material of Stranski-Krastanov (SK) on sub-monolayer (SML) InAs quantum dots (QDs). Four different heterostructures (A, B, C, and D) have been modeled using Nextnano software. Structures A, B, C, and D with the barrier material of GaAs, In0.15Ga0.85As, In0.25Ga0.75As, and In0.35Ga0.65As respectively have been taken into consideration. The barrier thickness has been kept constant at 7.5 nm for all the structures. The matrix material of In0.15Ga0.85As has been considered for InAs SML QDs. The biaxial and hydrostatic strain have been computed and compared. Lower magnitude of hydrostatic strain governs more carrier confinement in conduction band whereas, higher biaxial strain provides more splitting of heavy-hole and light-hole band. This results in more red-shifted photoluminescence. From the simulation results, it is observed that the biaxial strain is improved by 0.3704 % and the magnitude of hydrostatic strain is improved by 1.623 % in the InAs SK region of structure D as compared to that of structure A. Similarly, the biaxial strain is improved by 0.7677 % and the magnitude of hydrostatic strain is improved by 2.301 % in the InAs SML region of structure D as compared to that of structure A. The observed PL emission wavelength of structures A, B, C, and D were approximately 1549 nm, 1561 nm, 1572 nm, and 1584 nm respectively. Hence, the structure D provides the highest PL emission wavelength for LWIR telecommunication applications and optimal strain distribution among the other heterostructures.
We present a new concept of strain minimization through digital alloy capping layer (DACL) for the dot-in-a-well (DWELL) heterostructure. In this work, three different DWELL heterostructures with ternary capping of InxGa1-xAs have been simulated. The two analog DWELL structures with the indium (In) composition of 15% (Sample A1) and 45% (Sample A2), and one digital DWELL structure (Sample D1) with varying In composition from 45% to 15% in steps of 10 are considered. The bottom and top InGaAs well layer thickness of QD is considered to be 8 nm each. In digital sample D1, the bottom and top well layer is equally divided into 4 sub-parts, each having the thickness of 2 nm. The biaxial strain in sample D1 is increased by 0.66% and reduced by 2.95% and hydrostatic strain in sample D1 is reduced by 5.14% and increased by 3.49% when compare to their analog counterparts A1 and A2 respectively. Higher biaxial strain indicates the increased spacing between the heavy-hole and light-hole band in valence band, which would result in red-shifted photoluminescence. Lower hydrostatic strain ensures deeper electrostatic potential facilitating higher activation energy. The sample D1 provides the gradual strain relaxation inside the top and bottom InGaAs well layer. The emission wavelength of 1394, 1547, and 1514 nm is observed for samples A1, A2 and D1 respectively. The overall strain distribution inside the heterostructure is smoothly minimized in steps which would result in defect free heterostructure and hence will provide longer emission wavelength for SWIR applications.
This study presents a novel approach to enhance the photoluminescence and minimize strain in selfassembled bilayer InAs quantum dot (QDs). To obtain this approach, multi-level digital alloy capping layer (DACL) is introduced in the growth of the ternary InGaAs capping layer having different material composition, instead of conventional thick layer. A single thick 4 nm InGaAs capping on the InAs QD layers (Sample A1) is divided into four equal parts each having 1 nm thicknesses. The composition of indium (In) in strain reducing layer (SRL) in growth direction is varied from 45% to 15% for both first layer and second layer QDs (Sample D1). The experimental low temperature ground state emission wavelength for the sample A1 and sample D1 was 1096 and 1167 nm respectively. The biaxial and hydrostatic strain in growth direction was theoretically computed and compared for both analog and digital samples. The computed hydrostatic and biaxial strain in sample D1 is improved by 7.19% and 6.79% respectively, when compared to that of analog sample A1. The improved hydrostatic strain provides the better carrier confinement. The improved biaxial strain offers more band splitting between heavy-hole and light-hole band in valence band. This decreases the ground state band gap and thus offers a red shift in photoluminescence (PL). The experimental PL for both samples were also validated by simulating both heterostructures. The sample with DACL growth mode provided better crystalline quality, enhanced quantum yield and lesser defects.
In this study, we have discussed the effect of strain distribution and optical properties on In0.14Ga0.86As matrix thickness variation (tmat) in self-assembled InAs quantum dot (QD) heterostructure using temperature and power-dependent photoluminescence (PL) measurements. The calculated ground-state transition energies are 1.12, 1.14 and 1.09 eV for tmat of 2, 4 and 6 ML (monolayer) In0.14Ga0.86As matrix thickness respectively. We also discern that the full-width at half-maximum (FWHM) broadens gradually as temperatures increases due to electron-phonon scattering. The calculated activation energy (Ea) values are 231, 302 and 98 meV for increasing tmat. The partial strain relief due to varying In0.14Ga0.86As layer thickness occurs due to QD size tunability by preventing Indium (In) segregation effect, that sets the possibility to understand about InAs inter-band and intersubband transitions of PL emission. This has been validated with HRXRD results where strain decreases linearly with increasing tmat. Here In0.14Ga0.86As layer acts as a strain-reducing layer (SRL) in QD heterostructure as well. Thus helps in reducing the hydrostatic strain (∊hyd) of InAs QDs, while the lower InGaAs layer increases the QD density, leading to a remarkable rise in PL intensity due to state filling of carriers. The effect of strain distribution for varying tmat in the heterostructure was also studied using nextnano++ simulations. The relative percentage change in hydrostatic (biaxial) strain was calculated to be 5.5% (8%) respectively. Thus, the results so obtained can help in tuning matrix thickness on the PL emission properties of QDs and therefore in the realization of several optoelectronic devices.
We have investigated the effects of varying facet angle of the truncated pyramidal QDs on the strain and energy band profile. The conventional truncated QD pyramid has a height of 3 nm with the facet angle of 51˚ along with base and top width of 15 and 11 nm respectively, as observed from the previously reported transmission electron microscopy images. Also, the simulated results were validated with reported experimental data for reliability of our work. Five different angle variations viz. 41˚, 45˚, 51˚, 56˚, 61˚ were considered, referred as structure A, B, C, D and E. It is observed that the magnitude of hydrostatic strain is reduced by 1.22% for the structure E (facet angle of 61˚) and increased by 1.507% for structure A (facet angle of 41˚), when compared with the conventional structure C. Therefore, the carrier confinement would be better in case of structure E as compared to its counterparts. In comparison to structure C, the biaxial strain is 1.39% higher and 2.203% lower in case of structure E and A respectively. Higher biaxial strain would inculcate red shift in emission wavelength because of the movement of heavy-holes upward in energy, which is reflected from the computed photoluminescence peaks. The emission wavelength obtained for structures A, B, C, D and E were approximately 1140, 1151, 1155, 1161 and 1183 nm respectively. Thus, among all, structure E offered longest emission wavelength and optimum strain distribution within the heterostructure.
In this study, the concept of analog and digital alloy capping with ternary alloy InxGa1-xAs has been utilized in capping layer of InAs QDs. The composition of indium (In) in the capping layer having thickness of 8 nm, was kept constant in case of analog alloy technique. While, in digital alloy technique, In composition was varied from 0.45 to 0.15 in steps of 0.10 (Structure D1) having a thickness of 2 nm each. Validation of simulated results with previous experimental data was carried out to check accuracy of the present work. The hydrostatic and biaxial strains in growth direction were computed and compared. The magnitude of hydrostatic strain is reduced by 4.115% and biaxial strain is increased by 0.62% in the QD region of structure D1 as compared to structure A1. This indicates better carrier confinement and longer emission wavelength in structure D1 as compared to structure A1. Structure D1 provided an increment of hydrostatic strain by 3.41% and a decrement of biaxial strain by 2.56% in the QD region as compared to structure A2. Structure D1 with digital capping alloy provides a gradual strain relaxation in the capping layer due to systematic variation of In composition, ensures strain relaxation profile throughout the heterostructure by minimizing the lattice disparity in subcapping layers. The computed emission wavelength of structure A1, A2, and D1 were 1224, 1313, and 1287 nm respectively. The digital alloy technique would help in minimizing strain distribution within the heterostructure and results in defect and dislocation free heterostructure.
This study examines the photoluminescence (PL) properties and strain distribution in InAs/InGaAs heterostructure for varying number of sub-monolayer (SML) quantum dot stacks (nSML). High resolution x-ray diffraction (HRXRD) probes the strain effects, whereas PL spectroscopy evaluated the optical response. The ground-state transition energies calculated from PL experiments were found to be 1.19, 1.13, 1.11, 1.12 eV for 4, 6, 8 and 10 stacks respectively. It was observed that, with the increasing nSML, the PL peak emission energy has an initial blue shift and later a red shift, due to build-up of strain energy propagating from the bottom layers of InAs quantum dots (QDs). The activation energies (Ea) calculated from temperature-dependent PL (TDPL) measurements are 414, 279, 260 and 231 meV for 4, 6, 8 and 10 stacks respectively. The Raman characterization results explores on the strain relaxation effects by observing the shift and broadening in TO and LO phonon peaks of GaAs bulk material. The strain energy distribution along the growth direction (z-direction) was studied using nextnano++ simulations. The relative change in hydrostatic and biaxial strain at a particular z - position was calculated to be 3.2% and 5.5% respectively These strain components are of prime importance in understanding the position of conduction and valence band energy levels and finally the band gap energy. Thus, with these articulated results, we conclude that sample with 6 SML stacks is the optimum choice for fabricating optoelectronic devices operating in long range infrared telecommunication regime.
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