Free-exciton spectra in heteroepitaxial ZnSe/GaAs layers

Abstract

The free-exciton photoluminescence ͑PL͒ and reflection spectra of metal-organic vapor-phase-epitaxy grown ZnSe/GaAs epilayers with a thickness greater than that of the strain relaxation thickness were studied experimentally and theoretically for temperatures in the range Tϭ10-120 K. Calculations were performed in the framework of absorbing and reflecting dead layer models, using single and two-oscillator models, both including and neglecting spatial dispersion. The results rule out the explanation that the fine structure in the freeexciton PL spectra derives from thermal strain splitting and polariton effects, if this structure is not accompanied by a corresponding structure in reflection. It was shown that this structure in the PL spectrum originates mainly from light interference caused by the presence of a dead layer in the near-surface region, with the thickness of the dead layer depending on the excitation intensity. A correlation between the measured and inherent free-exciton spectra was established.

Exciton Diffusion in GaN Epitaxial Layers

“…Analysis of the line shape of free exciton photoluminescence and reflection spectra (RS) can provide a way for the determination of energy structure and estimation of the basic parameters of radiative recombination processes [1,2]. Most of the works have reported on identification of the free exciton states in GaN epitaxial layers in reflection, photoreflection and PL measurements [2][3][4][5]. However many fundamental parameters of exciton states in GaN are still insufficiently investigated.…”

“…However, the study of exciton diffusion processes in GaN encounters experimental difficulties [7]. It was demonstrated in our previous work [2] that analysis of the exciton PL and reflectance line shape in ZnSe epitaxial layers can provide us with this data. This method was applied in the present work to the investigation of the optical spectra of GaN epitaxial layers.…”

“…In accordance with (1) only three exciton parameters (S, t and D ex ) are varied during the fitting of the experimental PL if the complex dielectric functionẽ e w ð Þ near the A and B free-exciton resonance is known [2]. Functionẽ e w ð Þ can be described by the sum of the terms corresponding to contributions of the A and B free-exciton states [4].…”

Thickness dependence of exciton and polariton spectra from ZnSe films grown on GaAs substrates

“…[3][4][5][6][7][8][9][10] As compared to the PL spectra, the reflectance spectra of the exciton-polaritons in ZnSe/GaAs heterostructures were less investigated and the spectra are more complicated. [11][12][13][14][15] The existence of the exciton ''dead layer'' and the additional boundary conditions imposed on the polarization field near the sample surface can induce spike-like features. 11,16 -18 The interference of the polaritons scattered from different interfaces and surface can result in standing waves and alert the spectra dramatically.…”

“…[11][12][13][14][15] As compared to the fully strained films, the spectra from thick films are expected to be more complicated due to the close hh and lh energies and the interference. These effects may also affect the PL spectra in which the fine structures associated with both free and bound excitons have been observed.…”