Defect characterization of ZnBeSe solid solutions by means of positron annihilation and photoluminescence techniques

Abstract

Defect characterization of as-grown Zn1−xBexSe compound semiconductors was studied by positron lifetime and photoluminescence measurements. We obtain both experimental and theoretical evidence that the bulk lifetime of free positrons decreases linearly with Be alloying. The average positron lifetime increases with the temperature, indicating that both vacancies and negative ions trap positrons. The decomposition of the lifetime spectra shows that the positron lifetime of the vacancy decreases with an increase in Be content, as predicted by theoretical calculations. The concentration of vacancies and negative ions obtained from positron measurements follows the same trend with Be alloying. A comparison of positron measurements with theoretical calculations and photoluminescence experiments in Zn vapor annealed samples indicates that the vacancy corresponds to a Be vacancy. Besides, the negative ions trapping positrons at low temperatures have been attributed to Be interstitial atoms. The intensity of the B photoluminescence band correlates with the concentration of Be vacancies and Be interstitial atoms. We thus conclude that the electron levels of those defects are involved in the optical transition that leads to the B photoluminescence band.

Contactless electroreflectance and photoluminescence characterization of Zn0.68Be0.06Mg0.26Se crystalline alloys

“…a cation vacancy. The relative intensity of this DL band decreases with increasing Mg or Be content and noticeably decreases after annealing in zinc vapour at a temperature of 1230 K for 2 days [27]. Detailed investigation of near-band-edge PL spectrum at 10 K shows that the excitonic line can be deconvoluted into a free exciton line and a rather weak but well resolved shoulder-like feature assigned to the radiative recombination of the so called localized exciton (LX) in potential wells due to compositional disorder.…”

Photoelectric and photothermal investigations of Zn1‐x‐yBexMnySe solid solutions

“…For this reason, determination of the energy gap from luminescence data is not possible for crystals with high Mn content. The band at 2.35 eV is observed only at low temperatures (and for low Mn content) and is probably associated with cation vacancy related defect level as it was shown for Zn 1-x Be x Se and Zn 1-x Mg x Se crystals by positron annihilation and luminescence techniques [16,17]. The intensity of this band decreases after annealing in zinc vapour at temperature 1230 K for two days.…”

Growth and properties of Zn1–x –yBex Mny Se crystals

“…For this reason, determination of the energy gap from lumines- cence data is not possible for crystals with high Mn content. The band at 2.35 eV is observed only at low temperatures (and for low Mn content) and is probably associated with Be vacancy related defect level as it was shown for Zn 1-x Be x Se crystals by positron annihilation and luminescence techniques [4]. The intensity of this band decreases after annealing in zinc vapour at temperature 1230 K for two days.…”