Confinement Barrier Induced Enhancement in Thermal Stability of the Optical Response of InAs/InGaAs/GaAs Submonolayer Qu
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Confinement Barrier Induced Enhancement in Thermal Stability of the Optical Response of InAs/InGaAs/GaAs Submonolayer Quantum Dot Heterostuctures Debabrata Dasa, Hemant Ghadia, Sandeep Madhusudan Singha, Subhananda Chakrabartia* a
Centre for Nanoelectronics, Department of Electrical Engineering Indian Institute of Technology, Bombay Mumbai- 400076, India *Corresponding author: E-mail: [email protected]
Abstract: In this study the improvement in thermal stability of optical properties of InAs submonolayer quantum dot (SML QD) heterostructures is observed through incorporation of symmetric AlGaAs barrier layers. Low temperature photoluminescence (PL) spectra shows blue shift with less full width at half maxima, ascribe to the assimilation of AlGaAs barrier layers. The sample with confinement enhancing barrier shows the highest ground to ground transition energy with the lowest dot size distribution. Ex situ annealing of as grown samples, followed by PL analysis, confirms the improvement in thermal stability of optical behavior. For the samples with symmetric AlGaAs layer, annealing at higher temperatures under an inert condition can not change the downward transition energy effectively, whereas normal DWELL structures exhibits significant blue shift for the same. Introduction: From late 90s epitaxially grown self assembled quantum dot has become a popular research topic. It has the potential to be incorporated in many fields, like thermal imaging, solar photovoltaic, infrared LED and LASERs, quantum computing, photonic devices, etc. [1] Mainly three types of growth mechanisms (Volmer-Weber, stranski-krastanov (SK) and submonolayer (SML)) have been studied so far. Different growth strategy like bilayer, multilayer, dot in a well (DWELL), dot in a double well (DDWELL), dot with confinement enhancing barrier (CE), dot with current blocking barrier, overgrown of dots, etc., have been explored to optimize these quantum dot heterostructures for various purposes [1]. This strain assisted growth mechanism also brings different defects and dislocations into the heterostructures, which restricts the working efficiency of these quantum dot based devices. Few ex situ processes, like rapid thermal annealing (RTA) [2], pulsed LASER annealing [3] and light ion implantation[4], are there to improve the crystalline quality of as grown samples. Among them RTA is a well established process, owing to its inert processing environment. Here the as grown samples are annealed for a few seconds at an elevated temperature under Ar ambient. According with defect annihilation, this annealing process also promotes the inter diffusion of adatoms inside the heteroepitaxy. As a result the dot size and confinement energy modifies accordingly. The whole process sometime deviates the predefined upward or downward transitions of carriers. To reduce this thermal assisted inter diffusion, confinement enhancing AlGaAs barrier can be used in III-As based
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