Aniruddha Bhattacharya

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/cm^{2} in 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/cm^{2}. 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.

Electrical spin injection and detection of spin precession in room temperature bulk GaN lateral spin valves

We report 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.

Optical constants of In(x)Ga(1-x)N (0 ≤ x ≤ 0.73) in the visible and near-infrared wavelength regimes.

Complex refractive indices of In(x)Ga(1-x)N epitaxial layers have been determined from analysis of data obtained by spectroscopic ellipsometry. The measurements were made in the wavelength range of 400-1687 nm. The samples were grown by plasma-assisted molecular beam epitaxy on (001) silicon substrate and are of the wurtzite crystalline form. A comparison of the fundamental absorption edge derived from analysis of measured data and the measured photoluminescence peak emission energy indicates a Stokes shift present in the alloys.

The role of defects in lowering the effective polariton temperature in electric and optically pumped polariton lasers

The role of dislocations and defects in the material constituting the active region of an exciton-polariton laser has been examined and elucidated in the context of dynamic condensation and the temperature of the lower polariton condensate, TLP. For a GaN microcavity diode polariton laser operated at room temperature and characterized in this study, the value of TLP obtained from analysis of measured occupation in momentum space is 270 K, which is lower than the lattice temperature. Similar results from other room temperature GaN devices and GaAs-based polariton lasers operated at cryogenic temperatures are presented and discussed.

Room temperature GaN-based edge-emitting spin-polarized light emitting diode

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.