Effects of Low Energy Carbon Ion Implantation on the Material Properties of InAs/GaAs Quantum Dots with Variation in Cap
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Effects of Low Energy Carbon Ion Implantation on the Material Properties of InAs/GaAs Quantum Dots with Variation in Capping Layer S. Upadhyay1, A Mandal2, A. Basu3, P. Singh3 and S. Chakrabarti2 1 CRNTS, Indian Institute of Technology Bombay, Mumbai-400076, India 2 Electrical Engineering, Indian Institute of Technology Bombay, Mumbai-400076, India 3 IADD, Bhabha Atomic Research Center, Mumbai-400085, India ABSTRACT Under controlled irradiation of low energy carbon ions, photoluminescence (PL) study of InAs quantum dots prepared with different capping structures (GaAs and InAlGaAs) was carried out. Samples were investigated by varying implantation energy from 15 keV to 50 keV with fluence ranging between 3 × 1011ions/cm2 and 8 × 1011 ions/cm2. For fixed fluence of 4 × 1011ions/cm2, low temperature PL showed enhancement in a certain range of energy, along with a blue shift in the PL peak wavelength. In contrast, with varying fluence at fixed implantation energy of 50 keV, PL enhancement was not significant, rather a drop in PL intensity was noted at higher fluence from 5 × 1011 to 8 × 1011 ions/cm2. Moreover, carbon ion implantation caused a blue shift in the PL emission peak for both energy and fluence variations. PL intensity suppression was possibly caused by the formation of non-radiative recombination centers (NRCs) near the capping layer, while the corresponding blue shift might be attributed to stress generation in the capping layer due to implantation. As-grown and implanted InAlGaAs capped samples did not exhibit much variation in full width at half maxima of PL spectra; however, significant variation was observed for the GaAs capped sample. These results validate that InAlGaAs-capped QDs are more immune to ion implantation. INTRODUCTION Over the past years, self-assembled semiconductor quantum dot (QD) based devices, owing to their intrinsic sensitivity to normal incidence, have emerged as an alternate platform for quantum-well (QW) devices [1-3]. Low threshold current density of QD devices makes them suitable for application in infrared detection [4,5], and because they are tunable from 1500 to 1100 nm they work well in telecommunication applications [1,6]. Compared to their QW counterparts, QD-based optoelectronic devices have shown superior radiation hardness due to the three-dimensional (3D) quantum confinement of carriers in QDs. This unique property of QDbased devices is advantageous in devices used in radiation prone environments such as in space crafts, satellites, and nuclear power plants [7, 8]. Techniques such as rapid thermal annealing and pulsed laser induced annealing have been extensively used as post-growth methods to tune optical properties of InAs/GaAs dots. Sreekumar et al. [9] implanted heavy sulfur ion over single-layer InAs/GaAs QDs but found that irradiation with heavy ions degraded the material quality of QDs; hence, later they switched their focus to implantation with lighter ions such as hydrogen [10]. Majority of studies find that hydrogen implantation indeed improves the material
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