Ms. Anuja Singh Profile

Anuja Singh

at IIT Bombay

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Publications (2)

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Proceedings Article | 17 May 2022 Poster + Presentation + Paper

Quantum transport studies on type-II superlattice absorber configurations for infrared photodetection

Anuja Singh, Bhaskaran Muralidharan

Proceedings Volume 12139, 121391I (2022) https://doi.org/10.1117/12.2621533

KEYWORDS: Interfaces, Indium arsenide, Gallium antimonide, Superlattices, Photodetectors, Absorption, Scattering, Infrared radiation, Infrared photography, Sensors

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Photodetectors comprising of InAs/(In, Ga)Sb Type-II Superlattice (T2SL) structures demonstrate excellent performance over bulk detectors, which mainly includes tunable bandgap and controllable photo-absorption. The T2SL exhibits completely distinct properties from its constituent materials. In particular, the thickness of InAs and GaSb considered in one period of the T2SL plays a key role in determining its photoresponse. In this work, we compare two different compositions of the T2SL structure, which have similar bandgaps, in order to analyze their electronic band properties and miniband characteristics. For this, 12ML/12ML and 11ML/7ML T2SLs are examined which have a similar bandgap of 0.17eV corresponding to the wavelength of 7.2μm and the ratios of InAs-to-GaSb widths are approximately 1 and 1.5, respectively. The bandgap and density-of-states (DOS) masses are obtained by employing the k.p method within the envelope function approximation and the E-k dispersion both in the in-plane and the out-of-plane directions are analyzed. To further gain microscopic insights, we examine the carrier localization, miniband, and spectral current properties of finite T2SL structures using the Keldysh nonequilibrium Green’s function (NEGF) method. The spatial separation of electrons and holes in InAs and GaSb layers can be elucidated via the local density of states. Furthermore, a higher finite interband overlap between the first conduction band (C1) and the first heavy hole band (HH1) is observed in an 11ML/7ML T2SL which indicates a stronger absorption. Also, to predict the carrier transport in these structures, we incorporate scattering processes via the momentum dephasing model and note a lesser broadened dark current spectra in the 12ML/12ML T2SL structure. This suggests a stronger localization of carriers and as a consequence, the dark tunneling current will be indeed be suppressed in this T2SL.

Proceedings Article | 5 March 2021 Poster + Paper

Optimization of InAs dot-in-well structure for superior structural and optical performance

Debiprasad Panda, Anuja Singh, Ajay Kumar, Jhuma Saha, Subhananda Chakrabarti

Proceedings Volume 11680, 116801M (2021) https://doi.org/10.1117/12.2583388

KEYWORDS: Indium arsenide, Heterojunctions, Quantum dots, Mid-IR, Absorption, Quantum well infrared photodetectors, Photodetectors, Oscillators, Optical properties, Luminescence

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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 In_0.15Ga_0.85As 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 structures. There is a redshift in the absorption peak with thicker wells, but a cutoff in the absorption coefficient value is obtained as the well thickness is increased beyond 6 nm in both cases. The probability density functions of the carriers in the case of 6/6 nm symmetric DWELL are high, which attributes to higher oscillator strength. Thus, the 2/6 nm asymmetric DWELL is the optimum one and hence the corresponding QDIP is grown. The photoluminescence result has good match with the simulated result and the QDIP showed a mid-wave infrared (MWIR) photoresponse.

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