G. V. Mikhailov

Trionic Gain in δ-Doped ZnSe Quantum Wells

This paper reports on the observation of optical gain due to charged excitons (trions) in quantum wells. The specific optical coupling of the trion gives rise to stimulated emission on the low-energy wing of the trion photoluminescence line without degeneracy and inversion in the total particle numbers. Gain values as large as 10 4 cm -1 are found for excitation intensities of a few kW/cm. Higher injection levels lead to carrier heating which limits the available gain. A calculation of the absorption-gain crossover based on a kinetically determined equilibrium of excitons, trions and electrons with a common carrier gas temperature describes the experimental data well.

High‐Excitation Effects in the Optical Properties of δ‐Doped ZnSe Quantum Wells

The influence of high-density optical excitation on n-doped ZnSe/(Zn,Mg)(S,Se) quantum wells is studied by quasi-stationary photoluminescence and pump-probe experiments. In photoluminescence, the trion and exciton transitions saturate weakly with increasing excitation density. This is accompanied by superlinearly growing low- and high-energy wings attributed to collisions in the dense system of excitons, trions and carriers. For non-resonant excitation, a strong heating of the background carrier gas takes place and collisions lead to an effective recombination already during the relaxation of the electron-hole pairs down to the bottom of the band. This process limits reachable exciton and trion densities under quasi-stationary excitation.

TEMPORAL DYNAMICS OF EXCITON–TRION SYSTEM

Time-resolved and time-integrated circularly-polarized photoluminescence of excitons and trions have been studied in external magnetic fields up to 10 T. ZnSe-based quantum well structures of n-type with carrier densities varied from 5×109 to 1011cm-2 were used in this study. Absence of the chemical equilibrium in the exciton–trion system has been demonstrated at low temperatures (<10 K). The recovery of the equilibrium has been found at elevated temperatures (<15 K).

Giant linear polarization of photoluminescence in type-II ZnSe/BeTe superlattices

The photoluminescence spectra of type-II ZnSe/BeTe superlattices are investigated. Giant linear polarization of the luminescence is observed with unpolarized excitation in the spatially indirect exciton region. The effect is interpreted in a model of the general optical anisotropy of heterostructures with no common atom at the interfaces.

Optical gain and lasing of trions in delta-doped ZnSe quantum wells

The observation of optical gain at the trion transition of n-doped ZnSe quantum wells is reported. The specific optical coupling between the trion and electron band gives rise to stimulated emission on the low-energy wing of the trion photoluminescence band without degeneracy and inversion in the total particle numbers. Gain values as large as 104 cm-1 are found for excitation intensities of some kW/cm2. A calculation of the absorption-gain crossover photon energy based on a kinetically determined equilibrium of excitons, trions and electrons with a common carrier gas temperature describes the experimental data well.

Photoluminescence of InAs quantum dots grown on disoriented GaAs substrates

The photoluminescence spectra in an external magnetic field of an ensemble of InAs quantum dots grown by molecular beam epitaxy on a (001) GaAs substrate with a disorientation in the [010] direction are studied. A redistribution of the photoexcited carriers among different groups of dots under the influence of the magnetic field is observed. The concentration of quantum dots is determined by analyzing the data.