A. R. Goñi

High-gain excitonic lasing from a single InAs monolayer in bulk GaAs

We report the observation of highly efficient laser emission from a single InAs layer with an effective thickness of 1.5 monolayers (ML) embedded in bulklike GaAs. Lasing action is obtained at the wavelength of the InAs thin-layer luminescence (870 nm) by cw optical pumping with a threshold power density of 0.9(3)u2009kW/cm2 at 10 K. Gain measurements yield a very high material gain of 1.0(5)×104u2009cm−1 for the InAs layer when pumped with ∼10u2009kW/cm2 at low temperatures. The 0 dimensional character of the emission as determined from cathodoluminescence and the absence of band-gap renormalization with increasing pump level speak for an excitonic mechanism of population inversion.

Magnetoluminescence Study of Annealing Effects on the Electronic Structure of Self-organized InGaAs/GaAs Quantum Dots

We have studied the effects of annealing a self-organized InGaAs/GaAs quantum dot sample between 580 and 700°C by magnetoluminescence measurements at 2 K and fields up to 15 T. High-excitation power density luminescence spectra reveal up to three features in addition to the ground-state emission arising from radiative recombination processes between excited states of the quantum dots. With increasing annealing temperature all emission lines shift to higher energies while varying their splittings indicating a systematic increase in volume and Ga content of the dots. From the diamagnetic shift and the Zeeman splitting of the ground-state emission we obtain an increase of the spatial extent of the exciton wave function but a decrease of the effective g-factor upon annealing. The magnetic field splittings of excited-state transitions exhibit a strong dependence on annealing and are well accounted for within a simple oscillator model with total angular momentum mainly determined by the dot envelope functions.

Exchange instability of the two-dimensional electron gas in semiconductor quantum wells

A two-dimensional (2D) electron gas formed in a modulation-doped

Coupling of intersubband charge-density excitations to longitudinal-optical phonons in modulation-doped GaAs quantum wells

mathrm{GaAs}/{mathrm{Al}}_{x}{mathrm{Ga}}_{1ensuremath{-}x}mathrm{As}

Magnetoluminescence of Annealed Self-Organized InGaAs/GaAs Quantum Dots

single quantum well undergoes a first-order transition when the first excited subband is occupied with electrons, as the Fermi level is tuned into resonance with the excited subband by applying a dc voltage. Direct evidence for this effect is obtained from low-temperature photoluminescence spectra that display the sudden renormalization of the intersubband energy

Inelastic Light Scattering by Elementary Excitations of the 2D Electron Gas at High Densities

{E}_{01}

High-Pressure Raman Scattering of Biaxially Strained GaN on GaAs

upon the abrupt occupation of the first excited subband. Calculations within density-functional theory, which treat the 2D exchange potential exactly, show that this thermodynamical instability of the electron system is mainly driven by intersubband terms of the exchange Coulomb interaction, thus being a unique but fundamental property of an electron system with more than one occupied subband.

Effect of an electric field on electronic excitations in double quantum wells

We have investigated the interaction between the longitudinal-optical (LO) phonon and the lowest intersubband charge-density excitation of the two-dimensional (2D) electron gas formed in a modulation-doped single quantum well structure. The intersubband spacing is continuously increased by applying dc voltages up to about 200 V between a top gate and a back contact. The frequency of the LO-phonon mode confined to the quantum well exhibits an electron-density-dependent redshift which is attributed to enhanced screening effects by the 2D electron gas. Inelastic light-scattering spectra reveal a clear anticrossing behavior of the energies of LO-phonon and charge-density excitation, for which a coupling constant of 1.5(3) meV is obtained.

Wave vector dispersion of excitations of the two-dimensional electron gas from light scattering using a grating coupler

We have investigated the effects of annealing a self-assembled InGaAs/GaAs quantum dot sample between 580 and 700 °C by magnetoluminescence measurements at 2 K and fields up to 15 T. By using a high power density of about 5 kW/cm2 for the excitation of the luminescence we were able to observe up to three features in addition to the ground-state emission arising from radiative recombination processes between excited states of the quantum dots. With increasing annealing temperature all emission lines shift to higher energies while varying their splittings. The diamagnetic shift of the ground-state emission as well as the Zeeman splittings of excited-state transitions exhibit a strong dependence on annealing and clearly speak for an increase in volume and Ga content of the dots.

Effect of pressure on optical phonon modes and transverse effective charges inGaNandAlN

We have investigated the dependence on carrier density of elementary excitations of the 2D electron gas formed in a modulation-doped single quantum well structure. The 2D electron density n, as obtained from lineshape fits to the photoluminescence spectra, is continuously increased by applying dc voltages ranging from 5 to 100 V between the electron gas and a back contact. A substantial population of the second electron subband is revealed at high voltages by the strong redshift of the corresponding emission line due to bandgap renormalization effects. In this high-density regime, we observe a large reduction of the exchange-correlation term of the Coulomb interaction.