Vikas Pendem

Bio: Vikas Pendem is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Quantum dot & Spectroscopy. The author has an hindex of 4, co-authored 13 publications receiving 59 citations. Previous affiliations of Vikas Pendem include Central Electronics Engineering Research Institute & Academy of Scientific and Innovative Research.

Thermally Grown TiO 2 and Al 2 O 3 for GaN-Based MOS-HEMTs

Abstract: We have demonstrated the potential use of thermally grown TiO2 and Al2O3 oxides as gate dielectrics for GaN-based high-electron-mobility-transistors. TiO2 and Al2O3 are found to provide negative and positive band offsets with AlGaN, respectively. A significant performance improvement on various device characteristics provides evidence for its potential use. The oxides are formed by a combination of predeposition of a thin film and followed by oxidation in pure O2 environment. The formation and thickness of the oxides are confirmed through the X-ray photoelectron spectroscopy and the transmission electron microscopy. The performance improvement for TiO2- and Al2O3-based oxide gates have been identified in terms of a ideality factor and a reduction in the gate leakage current in comparison with that of control devices. This is further augmented by an increase in the ${n}_{s}\times \mu $ product. The ON/OFF current ratio and turn-ON voltage increase by 2–3 orders of magnitude and 0.3–0.6, respectively, for the Schottky diodes. The negative shift on the capacitance–voltage characteristics is also found to be minimal, indicating higher gate coupling with thermally grown oxides.

Strong Size Dependency on the Carrier and Photon Dynamics in InGaN/GaN Single Nanowalls Determined Using Photoluminescence and Ultrafast Transient Absorption Spectroscopy.

Abstract: Here, we have demonstrated strong size dependency of quasi-equilibrium and nonequilibrium carrier and photon dynamics in InGaN/GaN single nanowalls using photoluminescence and transient absorption spectroscopy. We demonstrate that two-dimensional carrier confinement, strain relaxation, and modified density of states lead to a reduced Stokes shift, smaller full width at half-maxima, increased exciton binding energy, and reduced nonradiative recombination. The ultrafast transient spectroscopy shows that carrier capture is a two-step process dominated by optical phonons and carrier–carrier scattering in succession. The carrier capture is a strongly size-dependent process and becomes slower due to modulation of the density of available states for progressively decreasing nanowall sizes. The slowest process is the electron–hole recombination, which is also extremely size-dependent and the rate increases by almost an order of magnitude in comparison to that of quantum-well structures. Electron–hole wave functio...

Theoretical modelling of exciton binding energy, steady-state and transient optical response of GaN/InGaN/GaN and AlGaN/GaN/AlGaN core–shell nanostructures

Abstract: Here, we present an efficient 1D model to describe carrier confinement in GaN/InGaN/GaN and AlGaN/GaN/AlGaN core-shell nanostructures (CSNs) within the effective mass framework. A self-consistent procedure combined with hydrogenic model is implemented to estimate exciton binding energy in these CSNs, as a function of CSN dimensions, polarization charge and alloy composition. A 3-fold higher exciton binding energy in these CSNs than that in planar counterparts is attributed to an increased electron-hole overlap. The trend exhibited by the exciton binding energy with polarization charge and alloy composition in the two types of CSNs is significantly different, owing to a drastic difference in the piezoelectric polarizations. A detailed investigation of the steady-state and transient optical response from these CSNs suggests that GaN/InGaN/GaN CSNs emit a wide spectrum. However, that is not the case with AlGaN/GaN/AlGaN CSNs owing to a relatively weaker quantum confined Stark effect. This study is aimed at providing accurate design strategies for UV-blue III-N CSN light-emitting diodes.

Determination of strain relaxation in InGaN/GaN nanowalls from quantum confinement and exciton binding energy dependent photoluminescence peak.

Abstract: GaN based nanostructures are being increasingly used to improve the performance of various devices including light emitting diodes and lasers. It is important to determine the strain relaxation in these structures for device design and better prediction of device characteristics and performance. We have determined the strain relaxation in InGaN/GaN nanowalls from quantum confinement and exciton binding energy dependent photoluminescence peak. We have further determined the strain relaxation as a function of nanowall dimension. With a decrease in nanowall dimension, the lateral quantum confinement and exciton binding energy increase and the InGaN layer becomes partially strain relaxed which decreases the piezoelectric polarization field. The reduced polarization field decreases quantum confined Stark effect along the c-axis and increases electron-hole wave-function overlap which further increases the exciton binding energy. The strong dependency of the exciton binding energy on strain is used to determine the strain relaxation in these nanostructures. An analytical model based on fractional dimension for GaN/InGaN/GaN heterostructures along with self-consistent simulation of Schrodinger and Poisson equations are used to theoretically correlate them. The larger effective mass of GaN along with smaller perturbation allows the fractional dimensional model to accurately describe our system without requiring first principle calculations.

Femto-second Carrier and Photon Dynamics in Site Controlled Hexagonal InGaN/GaN Isolated Quantum Dots: Natural radial potential well and its dynamic modulation

Abstract: Quantum dot (QD) is slated to play a significant role in quantum technologies through its usage as a single-photon source. It also has promising applications as efficient light emitters through str...

InGaN/AlGaN blue light emitting diodes

Abstract: Recently, we succeeded in producing for the first time, 1-cd-brightness blue InGaN/AlGaN light-emitting diodes (LEDs) suitable for commercial applications.1,5 In this report, co-doping with both Zn and Si into the InGaN active layer in InGaN/AlGaN LEDs in order to increase the output power of the InGaN/AlGaN LEDs is described.

Femtosecond studies of carrier dynamics in InGaN

Abstract: Ultrafast carrier dynamics in In0.16Ga0.84N were investigated using femtosecond transient transmission measurements. We observed a fast initial carrier cooling on a time scale of 500 fs followed by a slow relaxation process which persisted longer than 5 ps due to a hot phonon effect. Band gap renormalization induced transient absorption was observed using a probe photon energy 300 meV above the band edge. These results were compared to a model based on the numerical resolution of the carrier Boltzmann equations.

Ti/Au/Al/Ni/Au Low Contact Resistance and Sharp Edge Acuity for Highly Scalable AlGaN/GaN HEMTs

Abstract: In this letter, we have reported a novel metal scheme Ti/Au/Al/Ni/Au for ohmic contact on AlGaN/GaN high-electron-mobility transistors. The reported metal scheme is observed to show minimum metal out-diffusion and sharp edge acuity at high-temperature annealing, which facilitates aggressive scaling of source–drain separation ( ${L} _{\textsf {SD}}$ ). We have demonstrated ${L} _{\textsf {SD}}$ as low as 300 nm with gate length ( ${L} _{\textsf {g}}$ ) of 100 nm for this metal stack. We observed improvement in ON-resistance ( ${R} _{\mathrm{\scriptscriptstyle ON}}$ ) from 3 to $1.25~\Omega \cdot$ mm, transconductance ( ${g} _{\textsf {m}}$ ) from 276 to 365 mS/mm, saturation drain current ( ${I} _{\textsf {DS,sat}}$ ) from 906 to 1230 mA/mm, and unity current gain frequency ( ${f} _{\textsf {T}}$ ) from 70 to 93 GHz by scaling ${L} _{\textsf {SD}}$ from $3~\mu \text{m}$ to 300 nm. The gate lengths for all devices were 100 nm.

Giant Efficiency of Visible Second-Harmonic Light by an All-Dielectric Multiple-Quantum-Well Metasurface

Abstract: A high-efficiency nonlinear source of visible light in a multiple-quantum-well (MQW) metasurface is in high demand for photonic quantum technology, but existing systems suffer from the limited conduction-band offset of MQWs and high dissipative losses of metal, which severely limit applicability in the visible range. This study presents a simple, reliable system without metal losses, by utilizing the interband excitonic transitions of MQWs and the Mie resonances of the metasurface's structure. This shows a viable path toward a coherent, nonlinear light source for use in the visible region and beyond with high conversion efficiency, to enable nanophotonic quantum information processing.