Department of Electrical and Electronics Engineering

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Author: search.filters.author.Kumar, RahulSubject: search.filters.subject.Quantum well

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    Submonolayer InAs Quantum Dot Based Solar Cell: A New Approach Towards Intermediate Band Solar Cell
    (Bentham Science, 2023) Mourya, Satyendra Kumar; Kumar, Rahul
    This chapter summarizes the progress of InAs submonolayer (SML) quantum dot (QD) based intermediate band solar cell (IBSC). A brief background of intermediate band solar cells (IBSC) will be presented. Different IBSC prototypes will be discussed. The importance of quantum dots (QDs) for IBSC prototyping will be illustrated. An alternative of the most extensively used Stranski-Krastanow (SK)-QDs named SML QDs will be introduced. The fabrication of SML-QD-based IBSC will be discussed from the material point of view. We will also discuss the physics behind the improved performance of these SCs. Important research in this field will be reviewed. Finally, the future direction will be suggested to further improve the performance.
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    Temperature dependent optical properties of ultrathin InAs quantum well
    (Elsevier, 2024-10) Kumar, Rahul
    Temperature-dependent photoluminescence (TDPL) and time-resolved photoluminescence (TRPL) of ultrathin InAs quantum wells (QWs) in GaAs matrix have been investigated to understand the optical properties of carriers. Samples containing different thicknesses of InAs (0.5, 0.75, 1, 1.2, 1.4 monolayers) have been used for this study. The PL peak position of InAs with temperature does not follow the Varshni model at low temperatures. The activation energy (EA) of these QWs has been calculated from TDPL. As expected, the thinnest QW sample (0.5 monolayer) results in the smallest EA of 23 meV, whereas the thickest QW sample (1.4 monolayer) results in the highest EA of 79 meV. Carrier lifetime has been calculated from TRPL measurement for varying temperatures. At 10 K, the carrier lifetime increased almost linearly from 250 to 800 ps with the InAs QW thickness. Thicker InAs QW results in a longer carrier lifetime, which has been explained by the carrier escape model. Higher temperatures resulted in a decrease in carrier lifetime, which suggests carrier escape is dominating the temporal decay behavior.
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    2DEG modulation in double quantum well enhancement mode nitride HEMT
    (Elsevier, 2015-11) Kumar, Rahul
    A double quantum well (QW) based nitride HEMT has been conceptualized through numerical simulation of Schrödinger and Poisson's equations for enhancement mode operation by introduction of a deeper secondary QW along with primary AlGaN/GaN triangular potential well. The carriers for drain current are populated in the shallower primary QW through energy band bending with positive VGS. Participation of the concerned QW in drain current conduction depends upon the magnitude of the band offsets and polarization effects of the materials. Effect of the gate bias on energy band delineates the modulation of 2DEG carriers in the shallow energy quantum well from 1.6×10−3 cm−3 to 9.47×1017 cm−3 with gate bias from 0.5 V to 1.0 V to confirm the drain current conduction with Vth>+0.5 V at typical depth of source and drain Ohmic contacts.
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    GaAs layer on c-plane sapphire for light emitting sources
    (Elsevier, 2021-03) Kumar, Rahul
    High-quality cubic GaAs (111)A buffer layers have been grown on an atomically flat c-plane trigonal sapphire substrate having well-defined steps and terraces. A two-step growth method has been used where, at an early stage, a GaAs layer has been grown at low temperature (LT), followed by second high-temperature GaAs growth layer. In addition to the two-step growth process, an AlAs nucleation layer and multiple annealing steps have been employed. The effectiveness of the LT GaAs layer in this highly dissimilar epitaxy was then investigated. An LT GaAs layer resulted in a relaxed GaAs buffer with smooth surface morphology and high crystalline quality. An InGaAs quantum well (QW) was epitaxially grown on the 70 nm GaAs buffer and compared with a reference InGaAs QW grown on a GaAs (111)A substrate. Along with x-ray and high-resolution cross-section transmission electron microscopy, comparable QW photoluminescence intensity and linewidth with respect to reference InGaAs QW confirmed the effectiveness of our growth strategies to produce high-quality GaAs on sapphire. This demonstrates the opportunity for GaAs photonics on sapphire and the potential to realise an integrated microwave photonic chip on a sapphire platform.