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Gain Spectra in Photoexcited T-Shaped Quantum Wires

Nov. 15, 2005. Gain Spectra in Photoexcited T-Shaped Quantum Wires. Ping Huai @ Akiyama Lab. Problems to Solve. Gain Spectra of Quantum Wires with Many-body effect Realistic quantum confinement Coupling to waveguide or cavity.

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Gain Spectra in Photoexcited T-Shaped Quantum Wires

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  1. Nov. 15, 2005 Gain Spectra in Photoexcited T-Shaped Quantum Wires Ping Huai @ Akiyama Lab

  2. Problems to Solve • Gain Spectra of Quantum Wires with • Many-body effect • Realistic quantum confinement • Coupling to waveguide or cavity • Difference between Hartree-Fock and Free Electron Theory (Asada, Miyamoto, Suematsu)? • Effect of 1d DOS • Gain peak intensity, width, and position vs. carrier density and damping

  3. Lz Ly Lx Modal Gain of Single Quantum Wire in a Waveguide cgs lx ly Integration in both sides G ->2 ×2 × g spin Confinement factor

  4. Optical Properties of 2-Band Model Dk : Band Gap Renormalization (BGR) Conduction e Eb : Exciton Binding Energy Dk Eb Absorption without Coulomb hw=Eg0+ee,k+eh,k Absorption with Coulomb hw=Eg0+ee,k+eh,k-Dk-Eb Eg0 exciton h Ẽ=Ẽ0exp(-iwt) Heavy Hole Dipole moment

  5. FE and HF Theory Thermal Fermi Distribution ne,k = fe,k nh,k = fh,k Quasi-Equilibrium Condition Free Electron (FE) Hartree-Fock (HF) • Space-Filling factor : 1-fe,k-fh,k (FE and HF) • Band Gap Renormalization (BGR) : Dk (HF) • Exciton binding energy

  6. Gain/Absorption Calculation FE HF Parameters: Finite width: g (Å)

  7. Arm Well AlxGa1-xAs Quantum Wire Stem Well Coulomb Potentials in T-Shaped Quantum Wires Ground State (Lx=Ly=0.5a0) Confinement Potential Lｘ Lｙ Long wavelength limit ka0 <<1 Short wavelength limit ka0 >>1

  8. (1a) Gain Spectra in T-Shaped Quantum Wires Unit of energy E0=4.2meV (1b) In room temperature: gain • High carrier density: • HF: broad gain peak, red shift (BGR), low gain peak • FE: sharp gain peak, no shift density • Low carrier density: • HF: strong absorption peak (exciton) • FE: broad absorption (1d DOS) absorption

  9. Gain Spectra in Rectangular Quantum Wire Lz Ly Lx

  10. Gain Peak Vs. Carrier Density • HF: • Lower gain peak in high density. • Lower transparency density, but smaller slope dG/dN. • FE: • Higher gain peak in high density. • higher transparency density, larger slope.

  11. Gain Peak Vs. Damping • Gain peak intensity • HF: insensitive to g • FE: very sensitive to g • HF theory predicts large gain in room temperature (g=4.2meV)

  12. Summary & Discussion • Coulomb interaction has strong effect on gain spectra. • HF theory predicts (vs. FE): • Sharp exciton peak in case of low carrier density. • Lower transparent density. • Lower & broad gain peak. • gain peak insensitive to damping. • Dipole moment relation to polarization. • Temperature dependence needs to be clarified. • Plasma screening of Coulomb interaction. • Dynamical screening of Coulomb interaction.

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