Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Silicon doped with Tellurium (Te), a deep level impurity, at concentrations higher than the solid solubility limit (hyperdoping) was prepared by ion-implantation and nanosecond pulsed laser melting. The resulting materials exhibit strong sub-bandgap optical absorption showing potential for room-temperature broadband infrared photodetectors. As a thermodynamically metastable system, an impairment of the optoelectronic properties in hyperdoped Si materials occurs upon subsequent high-temperature thermal treatment. The substitutional Te atoms that cause the sub-bandgap absorption are removed from the substitutional sites to form Te-related complexes. In this work, we explore the phase evolution and the electrical deactivation of Te-hyperdoped Si layers upon furnace annealing through the analysis of optical and microstructural properties as well as positron annihilation lifetime spectroscopy. Particularly, Te-rich clusters are observed in samples thermally annealed at temperature reaching 950 °C and above. Combining the analysis of polarized Raman spectra and transmission electron microscopy, the observed crystalline clusters are suggested to consist of Si2Te3. The defect characterization using positron lifetime spectroscopy suggests the generation of vacancy complexes as a function of temperature, leading to the decrease of sheet carrier concentration.