Luminescence and electrical properties of MgxZn1-xTe alloys

Abstract

The luminescence and transport properties of high-quality undoped and phosphorus-doped Zn 1-x Mg x Te alloys (x ≤ 0.50) have been investigated. At 4.2 and 300 K, the photoluminescence of unintentionally doped crystals is dominated by near-band-edge recombination mechanisms. In phosphorus-doped samples, the luminescence spectra exhibit free-bound transitions involving shallow acceptor centers (phosphorus in tellurium sites). When x and/or T increases, a broad luminescence band also appears at lower energy (1.7-1.9 eV) which decreases the near-band-edge luminescence efficiency. This low-energy band could be due to phosphorus atoms occupying other sites in the lattice (metal sites, for example) and then acting like deep recombination centers. Such a behavior could also explain the electrical properties of phosphorus-doped crystals. The introduction of phosphorus leads to an increase of the free hole concentration p as compared to undoped crystals but all phosphorus atoms do not behave as shallow acceptors; an increasing fraction of these atoms would act like donors in sites other than the tellurium sites as x increases. In undoped materials, p decreases drastically when we add more magnesium and the hole mobility remains approximately constant. We think that this effect is due to compensation by residual donor impurities. On these undoped samples, light-emitting diodes (LED's) have been successfully obtained for the first time. Their quantum efficiency is reasonable if we take into account the low carrier concentration of the material. The emission peak position is 5390 A for Zn 0.9 Mg 0.1 Te instead of 5550 A for undoped ZnTe.