Depth-dependent eigenenergies and damping of excitonic polaritons near a semiconductor surface

Abstract

This paper reports the experimentally observed change of exciton-polariton eigenenergies near the surface of a semiconductor. Normal-incidence-reflection spectra and attenuated-totalreflection (ATR) spectra are measured in the n =1 exciton-polariton energy region. It is shown that ATR spectra probe regions near the surface whereas reflection spectra probe more deeply into the crystal bulk. Model calculations"which include spatial dispersion and depth-dependent eigenenergies and damping of excitonic polaritons, yield excellent agreement with experiments for various semiconductors. This agreement proves that reflection spectra are determined not only by bulk properties of excitonic polaritons, but reveal also the properties of the transition region at the crystal surface. Therefore, information extracted so far from reflection spectra about additional boundary conditions of excitons and exciton-free surface layers may have to be revised.

Effect of polycrystallinity on the optical properties of highly oriented ZnO grown by pulsed laser deposition

“…Our interpretation of the origin of exciton energy shifts in the PLD samples is in good agreement with theoretical descriptions of the effect of electric fields on exciton energies [18,19]. In reference 18, a universal curve relating the change in exciton energy to the electric field in the sample is given (as a multiple of the ionisation field, corresponding to a potential drop of 1 Rydberg across the exciton Bohr radius, when substantial exciton ionisation begins).…”

“…The residual n-type carrier density in ZnO films grown by PLD on sapphire is generally in the range > 5 x 10 17 cm -3 [6,9] and the typical potential barriers between grains, associated with these depletion regions, is ~ 0.5 eV [21]. Using these figures and the static dielectric constant of ZnO [19], we can estimate that the electric fields in the depletion layers will be ~ 400 x 10 3 V/cm. Thus we are confident that the electric fields in our samples have values equal to or greater than the ionisation field for the excitons and that the consequent energy perturbations and damping predicted by theory are fully consistent with our data.…”

“…Visual inspection of the reflectance anomalies shows that there is certainly substantial exciton damping for both A-and B-excitons, which is known to occur for electric fields greater than or equal to the ionisation field [19]. However we can make an independent check of the rough magnitude of the electric field and the ZnO ionisation field as follows.…”

Nature of Sub-Band Gap Luminescent Eigenmodes in a ZnO Nanowire

“…The resonant frequencies (for A, B, and C excitons) were taken as for a macroscopic ZnO crystal 20 with the resonance frequencies shifted to room temperature. We approximated the hexagonal ZnO nanowire by a nanowire cavity with a rectangular cross section with k⊥ ) π/d as the wavevector perpendicular to the nanowire long axis (d is the nanowire diameter).…”

Excitonic giant Zeeman effect inGaN:Mn3+

“…The exact energy of the excitonic transitions is neither the energy of the reflectivity maxima (see the position of transverse polaritons in Ref. 16) nor that of the peaks in the derivative of the absorption spectra. However, since the shape of the excitonic features appears to be not affected by the applied field, selecting arbitrary a position within the observed feature results only in a constant shift.…”