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 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

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

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

Thermal Fermi Distribution 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

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

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

Gain Spectra in T-Shaped Quantum Wires Unit of energy E0=4.2meV (1a) (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

Gain Spectra in Rectangular Quantum Wire Lz Ly Lx

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.

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)

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.