No abstract

No 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.

The structure of luminescence spectra of free excitons in CdS single crystals at T = 77 K is investigated. The dip formation is found in the top part of free A and B exciton resonant peaks of photoluminescence (PL) spectra after heating of the CdS crystals followed by fast cooling down to 77 K. Similar effects are observed when an external electric field is applied. It is shown that the structure of exciton PL spectra is due to self-absorption of resonance radiation in the near-surface layer with low exciton concentration. Our calculations demonstrate that the formation of an exciton concentration gradient may be caused by the influence of a surface electric field on the binding of electron-hole pairs to excitons. It is assumed that the increase of surface electric fields after heat treatment is caused by the thermostimulated adsorption of oxygen, which results in the formation of electron trap levels.

No abstract