It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

Optical properties of highly excited direct gap semiconductors

The dispersion of excitons, polaritons and biexcitons in direct-gap semiconductors

Spectra and decay kinetics of radiative recombination in CdS microcrystals

Optical investigations on excitons bound to impurities and dislocations in ZnO

A careful quantitative analysis of the reflectance of CdS crystals in the spectral range of the A-exciton is presented. Measured spectra for the isotropic and the mixed-mode orientation of the crystal are fitted by calculations based on the model of excitonic polaritons. Spatial dispersion and Pekar's abc, damping, exciton-free surface layers, and oblique incidence of light are considered simultaneously. The good agreement between theory and experiment confirms the model, the still existing discrepancies are due to the simplifying assumption of a homogeneous surface layer. The formulae needed are summarized, and the influence of the different polariton parameters on the calculated reflectivity spectra are discussed.



Es wird eine sorgfaltige Analyse des Reflexionsvermogens von CdS-Kristallen im Spektralbereich des A-Exzitons durchgefuhrt. Die gemessenen Spektren fur die isotrope Anordnung und die mixed-mode-Anordnung des Kristalls werden durch Rechnungen auf der Grundlage des Modells der Exzitonenpolaritonen angepast. Dabei werden raumliche Dispersion und Pekars abc, Dampfung, exzitonenfreie Oberflachenschicht und schrager Lichteinfall berucksichtigt. Die gute Ubereinstimmung zwischen Theorie und Experiment bestatigt das Modell, die noch existierenden Abweichungen beruhen auf der vereinfachenden Annahme einer homogenen Oberflachenschicht. Die benotigten Formeln werden zusammengefast und der Einflus der verschiedenen Polaritonen-parameter auf die berechneten Reflexionsspektren diskutiert.

A quantitative study of excitonic polariton reflectance in CdS

Emission and absorption spectra are measured of several ZnO-crystals in the region of bound-exciton complexes near the band gap. From Zeeman-effect studies up to 8 T at several angles between the c-axis of the crystal and the magnetic field most of the observed spectral lines are identified. The electron g-factor is found to be ge = 1.8, if the exciton is formed with a hole from the A-band, and ge = 2.1, if the exciton is formed with a hole from the B-band. The mass of the B-hole seems to be nearly equal to the mass of the A-hole.



Emissions- und Absorptionsspektren von ZnO-Kristallen werden im Gebiet der gebundenen Exzitonen in der Nahe der Bandkante gemessen. Aus Zeemaneffekt-Untersuchungen bis 8 T bei verschiedenen Winkeln zwischen Magnetfeld und c-Achse der Kristalle werden die meisten der beobachteten Spektrallinien identifiziert. Der g-Faktor des Elektrons ist ge = 1,8, wenn das Exziton mit einem Loch aus dem A-Band gebildet wird, bzw. ge = 2,1, wenn das Loch des Exzitons aus dem B-Band stammt. Das B-Loch hat ungefahr die gleiche Masse wie das A-Loch.

Zeeman Effect of Bound Exciton Complexes in ZnO

Mesure simultanee des spectres d'absorption et de reflexion entre 2,548 et 2,558 eV; determination du spectre d'amortissement par iteration et mise en evidence de son accord satisfaisant avec la vitesse de groupe des polaritons

M. Rosenzweig

Papers

A quantitative study of excitonic polariton reflectance in CdS

Zeeman Effect of Bound Exciton Complexes in ZnO

Transmission and Damping of Excitonic Polaritons in CdS

Experimental determination of additional boundary conditions for excitonic polaritons in CdS

Excitation spectroscopy of the green edge luminescence in CdS II. Low excitation intensity