Properties of gallium selenide single crystal

The photoluminescence of a large number of pure and doped single crystals of GaSe has been investigated in the temperature range from 4.2 to 300 °K with excitation intensities varying between 4·10−5 and 3·102 kW cm−2. The excitation was produced by the green line of a frequency doubled Nd: YAG laser. All crystals were grown in our laboratory, most of them by the Bridgman technique and some by transport reaction with iodine. Although no emission lines were found which were specific of the particular impurity introduced in the crystal, it was possible to classify the 4.2 °K spectra according to the amount of added impurities. Above 40 °K, the spectra of all crystals are identical. This dependence on temperature of the spectra is due to the rapid quenching between 20 and 40 °K of the luminescence resulting from recombinations at trap states and to the increasing importance at high temperatures of free-exciton recombinations. The two groups of lines associated with these two recombination channels constitute the principal part of all observed spectra. The variation of the spectra with temperature, pumping power and impurity content is interpreted as the result of a balance between the two recombination channels. A model of kinetics taking into account these two channels as well as the fact that the free exciton in GaSe resonates with the indirect minima of the conduction band is discussed in detail.

Photoluminescence of GaSe

Exciton-exciton and exciton-carrier scattering in GaSe

We describe a particular approach for the construction of a nonequilibrium statistical ensemble formalism for the treatment of dissipative many-body systems. This is the so-called Nonequilibrium Statistical Operator Method, based on the seminal and fundamental ideas set forward by Boltzmann and Gibbs. The existing approaches can be unified under a unique variational principle, namely, MaxEnt, which we consider here. The main six basic steps that are at the foundations of the formalism are presented and the fundamental concepts are discussed. The associated nonlinear quantum kinetic theory and the accompanying Statistical Thermodynamics (the Informational Statistical Thermodynamics) are very briefly described. The corresponding response function theory for systems away from equilibrium allows to connected the theory with experiments, and some examples are summarized; there follows a good agreement between theory and experimental data in the cases in which the latter are presently available. We also present an overview of some conceptual questions and associated criticisms.

A NONEQUILIBRIUM STATISTICAL ENSEMBLE FORMALISM MaxEnt–NESOM: Basic Concepts, Construction, Application, Open Questions and Criticisms

Optical functions of GaSc are derived from the Kramers-Kronig analysis of reflectivity data performed at quasi-normal incidence and at room temperature in the 2 to 80 eV range. Attempts of interpretation are suggested according to recent band structure calculations. In the experimental range, all the valence electrons are excited. On the high energy side, some structure corresponds to the excitation of 3d-electrons of Ga and Se, respectively. The calculated position of the plasmon peak is in good agreement with energy loss experiments.



Les fonctions optiques de GaSe sont calculees par l'analyse de Kramers-Kronig des mesures de reflectivite effectuees sous incidence quasi-normale et a temperature ambiante, entre 2 et 80 eV. Les essais d'interpretation sont bases sur de recents calculs de structure de bandes. Dans l'intervalle expeimental, tous les electrons de valence sont excites. Du cǒte des hautes energies, la structure correspond a l'excitation des electrons 3d de Ga et 3d de Se. La position calculee du pic de plasmon est en bon accord avec les experiences de pertes d'energie des electrons.

J.G.P. Ramos

Papers

Carrier assisted radiative recombination of free excitons in GaSe

‘Hot phonon’ contribution to Urbach's tails in semiconductors

Dependence of photoluminescence on hot excitations

Chemical-bond approach to the dielectric constant of Se and Te