Luminescence from free and self-trapped excitons in ZnSe 1- x Te x

Abstract

From the isoelectronic Te doped ZnSe crystals, ZnSe 1- x Te x , remarkable features are observed through the luminescence emission and excitation spectroscopy. First, a free exciton (FX) peak at 2.794 eV as well as the broad emission band having phonon structure peaking near 2.65 eV (blue band) is observed in the luminescence emission spectra. The intensity of FX luminescence increases with increasing temperature up to 40 K and above this temperature, it decreased exponentially, while that of the blue band gradually decreases. As another peculiar feature, excitation spectra demonstrate two peaks; one, the higher energy peak is at the position of the FX in the luminescence spectra, the other, the lower energy peak is coincident with the 1LO (longitudinal optical) phonon in the blue band. Furthermore, at a fixed probe energy (near the peak of the blue band), the ratio of the lower energy peak intensity to the higher energy peak intensity increases up to 40 K and decreases above this temperature. This type of excitonic behavior can be attributed to the dynamical process of excitons induced by Te atoms, which is quite different from that observed in other semiconductors.