E.A. Meneses

Dependence of hot carriers temperature on lattice temperature in CdS

Abstract Non-equilibrium carrier distributions were obtained in CdS at various temperatures from 77 to 400K. A study is made of the influence of the lattice temperature on the carrier temperature. It is found that the higher the lattice temperature the lower is the difference between carrier and lattice temperatures, though carriers are always thermalized among themselves. The results can be accounted for by carrier relaxation through optical polar phonon emission.

Band gap reduction in CdS due to high density of photo-injected carriers

Abstract At high photoexcitation levels the intrinsic radiative emission band in CdS, displays strong distortions which increase with excitation intensity. The two main features are a shift towards lower energies and a broadening of the lower energy side of the emission band. These effects are attributed to the high density of injected carriers

Carrier assisted radiative recombination of free excitons in GaSe

Abstract Photoluminescence spectrum of GaSe at very high excitation intensities displays two emission bands. At lower excitation levels emission is dominated by free exciton recombination. As the excitation increases the spectrum becomes dominated by recombination of an exciton-carrier complex. Arguments are based on line shape analysis, and spectral behaviour with temperature and excitation intensity.

Near band-edge optical properties of cubic GaN

We used photoluminescence, photoluminescence excitation spectroscopy (PLE) and photoreflectance (PR) to study the optical properties of thin films of cubic GaN, deposited by plasma-assisted molecular beam epitaxy on a GaAs (001) substrate. Our results show a clear step-like absorption edge, resulting from the merging of the free exciton with the continuum. Quantitative values for the absorption-edge energy and lifetime broadening are obtained. The dependence of the latter on temperature, as well as some features of the PR spectrum, reveal that the cubic material still presents residual strain and distortions. A secondary absorption-edge due to hexagonal inclusions is also observed in the PLE spectra.

Many-body effects in the radiative emission spectrum of semiconductors☆

Abstract We consider the effect of the interaction among photoinjected electrons, on the radiative emission spectra of semiconductors. The observed shift of the photoluminescence spectra, at high excitation levels, towards lower energies is accounted for by the present calculation.

Electron-hole liquid in GaS

Abstract Photoluminescence spectra of “pure” GaS are recorded under high excitation levels and low temperatures between 1.9 and 10K. This work reports a new and broad band which dominates the spectrum at high excitation intensities and temperatures near 1.9K. Its dependence on the excitation level is highly superlinear. When temperature is raised from 1.9 to 10K the spectrum observed of low excitation levels is recovered. We interpret the band here observed as due to radiative recombination from electron-hole droplets. From best fitting between experimental spectrum and calculated theoretical curves the critical density and the condensation energy are estimated as, nc = 4.5 × 1020 cm−3 and φ = 9.0 meV.

Dependence of photoluminescence on hot excitations

Abstract The high energy tail of the photoluminescence spectra of CdS in conditions of high photoexcitation intensities is studied. It is shown that the increasing excitation is a result of the simultaneous effect of non-equilibrium distribution of electrons and LO-phonons.

Exciton-plasma Mott transition in CdSe at 77K

Abstract Photoluminescence spectra of CdSe obtained in conditions of moderate excitation densities show anomalies in the behavior of peak position and intensity. These anomalies, on the basis of the optical gain and in the shift of peak position to lower energy side, are ascribed to the onset of an exciton-plasma Mott-transition in the photoexcited semiconductor.

Stimulated photoluminescence of CdSe

The stimulated emission from CdSe obtained under high excitation level has been investigated at 77K. The spectra obtained under N2 laser pumping shows a dominant P line (6920 A) which is ascribed to the onset of a high density plasma oscillation. This assignment is made on the basis of its optical gain and the shift of peak position to lower energy as pumping power increases. A study of the gain of the P line shows that at high excitation intensities superradiant processes dominate the emission.

Exciton-plasma Mott transition in ZnSe

Abstract Luminescence spectra of ZnSe obtained in conditions of high excitation densities show anomalies in the behaviour of peak position and intensity. These anomalies are ascribed to the onset of an exciton-plasma Mott-transition in the photo-excited semiconductor.