Electrical and optical properties of gold-doped n-type silicon

Different measurement techniques, both electrical and optical, were utilized in this work to characterize gold diffusion in n-type, float-zoned silicon in the temperature range 600-1150 °C. In the lower temperature region (≤750 °C), the gold diffusion is observed by the introduction of the Au acceptor state at 0.53 eV below the conduction band, and is correlated to the electrical behavior of the samples deduced from Hall effect and resistivity data. Also, the effects of Au diffusion on the free-carrier concentration and mobilities are discussed. It was shown that high temperatures and long times for gold diffusion change the conductivity type in the samples from n to p. In the samples that converted to p type, a limiting room-temperature resistivity of 2.0×10³ Ω cm was attained, when the conduction is mainly influenced by the Au-related deep electronic states in the band gap. In this case, the diffusion mechanism is also investigated by secondary ion mass spectroscopy data determining the equilibrium Au solubility, which is close to the equilibrium solubility of interstitial gold. Low-temperature photoluminescence measurements have shown that the intensity of the lines often attributed to dislocations, increases significantly by gold diffusion in the lower temperature region. At higher diffusion temperatures, a decrease of the dislocation-related lines was found, associated with formation of gold-related precipitates. Introducing an inhomogeneous internal stress distribution in the Si matrix, these precipitates cause line shifts as well as line broadenings of the free exciton, the phosphorus bound exciton, and the electron-hole droplet photoluminescence emissions. The concentration of substitutional phosphorus is found to decrease with increasing diffusion temperatures.