My research interests lie in the areas of solid-state physics and electronics, novel electronic and optoelectronic devices, quantum physics and nanotechnology. I am interested in exploring both the theoretical and experimental aspects of my research, which include design, experimental realization and characterization of novel electronic, optoelectronic and spintronic devices, thin film epitaxy and deposition, clean room processing and fabrication, quantum mechanical and semi-classical simulation and analysis of nano-scale electronic, optoelectronic and photonic devices and systems. A brief overview of some of my published research work is given below.

Optical interconnect using vertically grown periodic III-V nanowires on silicon

In this work, we study light propagation and coupling in a system of III-V nanowire array arranged vertically on a planer silicon waveguide, using two-dimensional (2D) and three-dimensional (3D) Finite-Difference Time-Domain (FDTD) techniques. The results of 2D analysis show that 82% light can be extracted from a waveguide of GaAs nanowire array, whereas the value is 40% for GaN nanowire array because of the lower refractive index of this material system. In the presence of a coherent source, the efficiency of light coupling from nanowire array to waveguide becomes 80% for GaAs and 57% for GaN nanowires. We also find that for efficient light coupling in both directions, less amount of material will be required in GaAs-based system due to the smaller-diameter-nanowire requirement for GaAs than for GaN.

Relevant publication:
  • D. Paul and M.Z. Baten, "Design and optimization of optical interconnect using vertically grown periodic III-V nanowires on silicon",  2017 IEEE International Conference on Telecommunications and Photonics (ICTP)

Room-Temperature Spin Polariton Diode Laser
A spin-polarized laser offers inherent control of the output circular polarization. We have investigated the output polarization characteristics of a bulk GaN-based microcavity polariton diode laser at room temperature with electrical injection of spin-polarized electrons via a FeCo/MgO  spin injector. Polariton laser operation with a spin-polarized current is characterized by a threshold of 69 A/cmin the light-current characteristics, a significant reduction of the electroluminescence linewidth and blueshift of the emission peak. A degree of output circular polarization of 25%
is recorded under remanent magnetization. A second threshold, due to conventional photon lasing, is observed at an injection of 7.2 kA/cm2. The variation of output circular and linear polarization with spin-polarized injection current has been analyzed with the carrier and exciton rate equations and the Gross-Pitaevskii equations for the condensate and there is good agreement between measured and calculated data.

Relevant publication:
  • A Bhattacharya, M Z Baten, I Iorsh, T Frost, A Kavokin, P Bhattacharya, "Room-Temperature Spin Polariton Diode Laser", Phys. Rev. Lett. 119, 067701 – Published 10 August 2017.

Room-Temperature Spin-polarized Light Emitting Diode 
In this work, room temperature circularly polarized electroluminescence is observed from bulk GaN-based double-heterostructure edge-emitting light emitting diodes operated with continuous-wave spin-polarized electrical injection. The measured in-plane magnetizing field-dependent output circular polarization in the quasi-Voigt geometry is coincident with the hysteresis characteristics of the spin-injector confirming electron spin injection in remanence from the n-type FeCo/MgO tunnel spin contacts. A peak output circular polarization of ~ 6 ± 1 % is measured at 300 K. 

Relevant publication:
  • A Bhattacharya, M Z Baten, T Frost, and P Bhattacharya, "Room Temperature GaN-Based Edge-Emitting Spin-Polarized Light Emitting Diode", IEEE Photoincs Technology Letters, Volume: 29, Issue: 3, Feb.1, 1 2017.

Nanowire Array Guided Photodiode on Silicon
III-nitride nanowire heterostructure arrays with multiple InN disk light absorbing regions have been grown by plasma-assisted molecular beam epitaxy on (001)Si substrates, and guided wave photodiodes have been fabricated and characterized. The spectral photocurrent of the devices has been measured under reverse bias, and the data exhibit distinct shoulders in the range of 0.69–3.2 eV (0.39–1.8 lm). The estimated responsivity at a wavelength of 1.3 lm is 0.2 A/W. The nanowire photodiode response was also measured with an excitation at one facet provided by an edge-emitting laser fabricated with the same nanowire array and emitting at 1.3 lm

Relevant publication:
  • A Hazari, M Z Baten, L Yan, J M. Millunchick, and P Bhattacharya, "An InN/InGaN/GaN nanowire array guided wave photodiode on silicon", Applied Physics Letters, 109, 191102, December, 2016.
        (representative SEM images of the nanowires are taken from the following publication)

Exciton-Polaritons in Semiconductor Microcavities
Excitons-polaritons or polaritons in semiconductor microcavities have been an area of intense research over recent years. When an
emitter in the form of bulk, quantum well, quantum wire or quantum dot is placed inside a suitably designed microcavity, the strong interaction between the confined light modes and the exciton states results in new eigenstates in the form of exciton-polaritons. The Bosonic nature of these quasi-particles
 can be exploited to study numerous phenomena related to cavity quantum electrodynamics and many-body physics, as well as to realize ultra-low threshold coherent emitters in the form of polariton lasers. Our studies in the area of exciton-polaritons have mostly focused on the experimental realization and theoretical understanding of electrically pumped polariton lasers, employing GaAs- and GaN-based material systems. Some of our key accomplishments in this area of research are the following.
  • Experimental realization of the first electrically pumped polariton laser which can operate at room temperature
  • Experimental realization of a GaAs-based electrically pumped polariton laser which operates at 155 K
  • First experimental study on the small-signal modulation response of a polariton laser diode
  • Characterization of the outptut polarization of polariton lasers under electrical injection
  • Experimental studies on the role of defects on dynamic condensation in polariton lasers
Relevant publications (selected):
  • A Bhattacharya, M Z Baten, I Iorsh, T Frost, A Kavokin, P Bhattacharya, "Output polarization characteristics of a GaN microcavity diode polariton laser", Physical Review B 94 (3), 035203 (2016).
  • M Z Baten, A Bhattacharya, T Frost, I Iorsh, A Kavokin, P Bhattacharya, "The role of defects in lowering the effective polariton temperature in electric and optically pumped polariton lasers", Applied Physics Letters 108 (4), 041102 (2016).
  • A Bhattacharya, MZ Baten, P Bhattacharya, "Electrical spin injection and detection of spin precession in room temperature bulk GaN lateral spin valves", Applied Physics Letters 108 (4), 042406 (2016).
  • M Z Baten, T Frost, I Iorsh, S Deshpande, A Kavokin, P Bhattacharya, "Small-signal modulation characteristics of a polariton laser",Scientific reports 5,  Article number: 11915 (2015).
  • M Z Baten, Pallab Bhattacharya, Thomas Frost, Saniya Deshpande, Ayan Das, Dimitri Lubyshev, Joel M Fastenau, Amy WK Liu, "GaAs-based high temperature electrically pumped polariton laser", Applied Physics Letters 104 (23), 231119 (2014).
  • P Bhattacharya, T Frost, S. Deshpande, M Z Baten, A Hazari, A Das, "Room Temperature Electrically Injected Polariton Laser", Phys. Rev. Lett., Vol. 112, pp. 236802 (2014 )
Electrical Spin-Injection and Detection in Semiconductors
Spintronics offer the possibility of realizing next generation electronic and optoelectronic devices for future quantum information
processing, logic circuits and memory devices. Among different semiconductor material systems, 
GaN is deemed to be a prospective candidate for room temperature spintronics applications. To this end, we reported the measurement of diffusive electronic spin transport characteristics in an epitaxial wurtzite GaN lateral spin valve at room temperature. Hanle spin precession and non-local spin accumulation measurements have been performed with the spin valves fabricated with FeCo/MgO spin contacts. Electron spin relaxation length and spin-flip lifetime of 176 nm and 37 ps, respectively, are derived from analysis of results obtained from four-terminal Hanle spin precession measurements at 300 K. The role of dislocations and defects in bulk GaN has also been examined in the context of electronic spin relaxation dynamics.

Relevant publication (selected):
  • A Bhattacharya, MZ Baten, P Bhattacharya, "Electrical spin injection and detection of spin precession in room temperature bulk GaN lateral spin valves", Applied Physics Letters 108 (4), 042406 (2016).

High Performance Quantum Dot Lasers in the Visible and Near-Infrared Regime
Quantum dots (QDs) are nanostructures in which carrier motion is restricted in all three spatial dimensions. Because of the three
An AFM image of InAs self-assembled quantum dots grown on InP substrate
dimensional quantum confinement, ideal quantum dots have delta-like density of states and can be employed to realize high performance semiconductor lasers. We have designed, expitaxially grown, fabricated and experimentally characterized GaN- and InAs-based quantum dot lasers which operate in the red and near-infra red region of the electromagnetic spectrum. 
We have investigated the characteristics of edge-emitting InGaN/GaN red-lasers with multi-dot layers in the active region. These devices exhibit an extremely low threshold current density of 1.6 kA/cm2, a high temperature coefficient T0 = 240 K, and a large differential gain of 9 × 10−17 cm2The maximum measured -3 dB small-signal modulation bandwidth of the InAs QD based lasers is 14.4 GHz. These devices  are characterized by a chirp of 0.6 Å for a modulation frequency of 10 GHz. These characteristics are amongst the best from any 1.55 μm edge-emitting semiconductor laser. Modulation doping of the dots with holes and tunnel injection of electrons have been incorporated in the design of the active (gain) region of these devices to improve their performance characteristics.

Relevant publication (selected):
  • T Frost, A Hazari, A Aiello, M Z Baten, L Yan, J Mirecki-Millunchick, P Bhattacharya, "High performance red-emitting multiple layer InGaN/GaN quantum dot lasers", Japanese Journal of Applied Physics 55 (3), 032101 (2016).
  • S Bhowmick, MZ Baten, T Frost, BS Ooi, P Bhattacharya, "High Performance InAs//InP Quantum Dot 1.55 Tunnel Injection Laser", IEEE Journal of Quantum Electronics 50 (1), 7-14 (2014).